Dissertations / Theses: 'Evoked potentials, Visual'

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Bergkvist, Linn. "Visual Evoked Potentials : Referensvärden och könsskillnader." Thesis, Umeå universitet, Biomedicinsk laboratorievetenskap, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-171567.

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O’Toole, Dennis Michael. "Removal of ocular artifact from visual evoked response recordings." Thesis, University of British Columbia, 1985. http://hdl.handle.net/2429/25502.

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Potentials generated by the eye cause unwanted artifact in Visual Evoked Response (VER) recordings. These artifacts often contaminate the data in a systematic way that can lead to spurious experimental results. Although it is widely agreed that ocular artifact must be accounted for, the methods used to deal with this problem are varied. The present study compared four methods used to control ocular artifact; blink rejection, eyes closed, subtraction and regression. Twenty normal, female subjects were tested twice within the same session. Subjects watched light flashes of 4 intensities; 2, 30, 80, and 240 ft lamberts. The lights were presented at 1 hertz, reached maximum brightness in 0.5 msec and lasted for 0.5 sec. During testing the VER, and electroocculographic (EOG) response generated by a blink, were recorded. In the blink rejection method, any VER epoch that contained blink artifact was excluded from the average. The eyes closed method consisted of having subjects watch the stimuli through closed eyelids. The subtraction method corrects blink artifact by digitally subtracting the averaged EOG from the EEG. The proportion of EOG subtracted was determined by the EEG/EOG ratio estimated while subjects blinked spontaneously in a darkened environment. The regression method determines what proportion of EOG is to be subtracted on the basis of the correlation between EOG and EEG within VER epochs. Two correction, factors are calculated, one to correct for vertical movements and one to correct for horizontal movements. The blink rejection method was found to be useful with subjects who had 40% or more blink-free epochs, but was an unreliable method for the majority of subjects. The eyes closed method was also found to produce poor VER data. The eyelids appear to attenuate the light reaching the retina and there may be eyeball movement despite having the eyes closed. Both the subtraction and regression methods substantially reduced the ocular artifact. Horizontal eye movements do not appear to be a significant problem over the short intervals of VER recording because the regression method was not superior to the subtraction method in removing artifact. Although the subtraction and regression methods effectively reduce ocular artifact, both are less effective at posterior electrode placements. The reason for this may be that ocular potential is not propagated across the scalp in a linear fashion, as often assumed. Using spontaneously generated blinks in a darkened environment, it was found that the ocular potential waveform changes shape as it moves towards the back of the head.
Arts, Faculty of
Psychology, Department of
Graduate

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Mackay, Alison. "Assessing children's visual acuity with steady state evoked potentials." Thesis, University of Glasgow, 2003. http://theses.gla.ac.uk/6573/.

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The majority of children attending ophthalmology clinics require a visual acuity assessment. The optimal technique depends on age as well as the ability to cooperate with testing. Most acuity assessments are performed subjectively by an orthoptist. Objective acuity assessment by Visual Evoked Potential (VEP) provides a complementary assessment in those subjects who cannot complete subjective tests. The aim of this study was to develop and evaluate a rapid, objective visual acuity assessment. The technique was named the step_ VEP and is based on the real-time analysis of steady-state VEPs (ssVEP). It presents high contrast checkerboard stimuli of sizes 0.4 to 3.0 LogMAR with a successive approximation algorithm. Speed of response detection, specificity and sensitivity were optimised by investigation of recording montage and analysis techniques in a group of normal children and adults (N=102). The success, duration and outcome of step_ VEP acuity assessment was compared to transient VEP (t-VEP) acuity assessment and subjective acuity assessment in a group of paediatric patients (N=218). I-D Laplacian analysis of three occipital electrodes was significantly faster than conventional recording and analysis (Oz-Fz) at detecting ssVEP responses near visual acuity threshold (3' checks) from three years upwards, and at detecting responses to 6' and 9' checks in the 7-9 year age group. A lateral electrode site at 15% of the half-head circumference was fastest most often in adults. Step_ VEPs were 16% more successful than t-VEPs and 9% more successful than subjective tests in providing a complete acuity assessment. Subjective acuity scores were systematically higher than VEP acuity scores in subjects who successfully completed both assessments. A closer agreement with subjective acuity scores was found for step_ VEPs than t-VEPs. The disparity between step_ VEP acuity score and subjective acuity score was shown to reduce with age.

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Calvert, Julie. "Visual evoked potentials in normal aging and Alzheimer's disease." Thesis, Glasgow Caledonian University, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.395798.

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Khalil, Nofal Mohammed. "Investigations of visual function in migraine by visual evoked potentials and visual psychophysical tests." Thesis, Imperial College London, 1991. http://hdl.handle.net/10044/1/8336.

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Simpson, David Gordon Giles, and dsimpson@swin edu au. "Instrumentation for high spatial resolution of steady state visual evoked potentials." Swinburne University of Technology, 1998. http://adt.lib.swin.edu.au./public/adt-VSWT20060711.123100.

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This thesis reports on several new and innovative instrumentation developments to solve some of the problems of brain activity monitoring, particularly SSVEP (Steady State Visual Evoked Potentials) studies. SSVEP systems generate suitable stimuli and record the resulting brain biopotentials from scalp electrodes. The instrumentation is configured as a 'Neuropsychiatric Workstation', supporting up to 136 scalp electrodes. Operating in the SSVEP mode, the Neuropsychiatric Workstation reported here significantly improves upon the previously reported spatial resolution and accuracy of maps related to the generated stimuli. These maps allows insights to be gained into the cognitive workings of the brain. A significant component of the work reported here covers the development of the multielectrode EEG measurement modules and the associated techniques for minimising interference and cross-talk. The techniques for synchronising recordings from all electrodes with the stimulus, interfacing to a host computer and real-time storage of the very large amounts of data generated to hard disk, are all reported. The SSVEP paradigm uses a sinusoidal-modulated visual stimuli. A novel linearised LED (light emitting diode) head-up display was developed, in addition to more conventional stimuli, such as the alternating checker-board display, all with sinusoidal modulation capability over a range of frequencies. The Neuropsychiatric Workstation described in thesis has been replicated several times and is in regular use at Brain Sciences Institute (BSI) at Swinburne University of Technology, and other collaborative research institutes.

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Matthews, David. "Dissociation of P300 brain potentials evoked by rare visual stimuli." Thesis, University of St Andrews, 1995. http://hdl.handle.net/10023/14732.

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The P300 event related potential (ERP) has consistently been dissociated into separate components on the basis of scalp amplitude distribution within the auditory modality (for instance Squires et al. 1975). A parietally maximum P300 deflection being evoked in response to target stimuli in comparison with a more frontally maximum P300 deflection evoked in response to rare nontarget stimuli. Results obtained within experiment 1 and 6 demonstrated such a dissociation employing auditory stimuli within a three stimulus oddball paradigm. It did not prove possible to obtain such a dissociation of P300 deflections on the basis of scalp amplitude distribution within the visual modality. Across a number of experimental manipulations both target and rare nontarget stimuli evoked P300 deflections with similar amplitude distributions (centro-parietal maximum along the midline). Experiment 5 demonstrated that frequent stimuli similarly evoked a centro-parietal maximum amplitude distribution. It was demonstrated that both stimulus probability (Experiment 4) and the physical characteristics of the stimuli (Experiment 5) affected the mean amplitude of the evoked P300 deflection. However, the scalp amplitude distribution of the evoked deflections remained constant. Within Experiment 6 it was demonstrated that within both auditory and visual modalities P300 deflections, evoked in response to both target and rare nontarget stimuli, demonstrated an equipotential amplitude distribution within an elderly group of subjects. In addition across both modalities amplitude evoked in response to rare nontarget stimuli demonstrated an asymmetric distribution across lateral chains of electrodes. Amplitude evoked along the right chain was significantly reduced in comparison to that evoked along the left chain. It would appear that the same, or a similar combination of, underlying neural generators are responsible for the activity that may be recorded at the scalp as the P300 deflection within the visual modality.

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Marshall, David. "Brain-computer games interfacing with motion-onset visual evoked potentials." Thesis, Ulster University, 2016. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.685554.

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A brain-computer interface (BCI) measures brain activity and translates this activity into commands for a program to execute. BCls enable movement-free communication and interaction with technologies. This thesis evaluates the effectiveness and limitations of motion-onset visual evoked potentials (mVEP) based BCI as a control method for brain-computer games interaction. MVEP incorporates neural activity from the dorsal pathway of the visual system which allows more elegant visual stimuli than other types ofVEP and has yet to be used in computer games. This thesis investigates ifmVEP can be used as a control method in multiple computer games, what genre of game is best for interaction with m VEP and can we correct problems with existing VEP BCI computer games? Before conducting experiments involving games of different genres an evaluation of the present stateof- the-art BCI games was carried out in an extensive literature survey on BCI games categorised by genre. The literature survey shows that 'action' is the most popular genre in BCI games (49% of BC I games) and provides both games developers and BCI experts a set of design and development guidelines for BCI games. The conclusions of the survey led to the development of three BCI games of different genres namely action, puzzle and sports. The testing of different BCI games using a single paradigm enables thorough assessment ofmVEP as a control method. Five mVEP stimuli are presented as buttons to allow the subject to choose from five possible actions in each game. The performance was assessed based on offline and online BCI accuracy and game score. The results indicate that players could control the games with reasonable online accuracy (66% average for 5 class classification, with an average training accuracy of 74%). The next study intended on improving the initial study's results by adding the mVEP to an on screen HUD (Heads up Display), training in the same game environment as the participants are tested within and adding a questionnaire. Results indicate that the players could control the games with an average online accuracy of 71 %, a significant improvement from the previous study. After further analysis of recorded data the ideal setup for mVEP games is defined with key specifications indicating between three and four channels is most economical setup without influencing accuracy whilst averaging over three trials (minimises latency in communication). Finally, through the evaluation of a range o,fthe games related surveys, we found that players enjoyed the m VEP puzzle game most, rating it both the most enjoyable and appropriate game with m VEP control. Overall this thesis shows that m VEP can be used in multiple games genres with good accuracy and provides players with an entertaining and novel control method for computer games.

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Lloyd, Robyn School of Optometry &amp Visual Science UNSW. "Achromatic and chromatic VEPs in adults with down syndrome." Awarded by:University of New South Wales. School of Optometry and Visual Science, 2005. http://handle.unsw.edu.au/1959.4/23957.

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Previous studies have found that spatial processing in children and adults with Down syndrome is different in comparison to the normal population. Some previous studies have also found that there is a high prevalence of colour vision deficiencies in people with Down syndrome. The aim of the present study was to use an objective test, the transient visual evoked potential (VEP), to assess achromatic and chromatic visual processing in adults with Down syndrome. Achromatic VEPs were recorded in response to black-white stimuli presented in patternreversal mode. Chromatic VEPs were recorded in response to two types of colour pattern, presented in pattern onset-offset mode. The two colour types were intended to preferentially stimulate the two principal chromatic pathways of the visual system, the ???redgreen??? and ???blue-yellow??? colour-opponent pathways. These stimuli are here termed the ???LM??? and ???S-(L+M) stimuli, respectively, reflecting the cone types that input to the pathways they are intended to stimulate. Each subject also completed two subjective colour vision tests, the Colour Vision Test Made Easy (CVTME) and the City University Colour Vision Test (CUT). Morphology of the achromatic and chromatic VEPs was found to differ between the group with Down syndrome and an age-matched control group. The latency of the P100 component of the achromatic VEP was found to be significantly later in the group with Down syndrome compared to the control group (the N75 latency was earlier in the group with Down syndrome, but not significantly so). The group-averaged peak-to-peak amplitude of the achromatic VEP was significantly lower in the group with Down syndrome compared to the control group. The major positive component of the VEP in response to the L-M stimulus was of significantly longer latency compared to that of the control group. The major negative component and the peak-to-peak amplitude of this response were not significantly different between the groups. For the response to S-(L+M) stimuli, the latency of the major negativity was significantly earlier in the group with Down syndrome and the major positivity was later, but not significantly so. Amplitude of this response was significantly higher in adults with Down syndrome compared to the control group. Most subjects in both groups passed both the CVTME and CUT. Our findings indicate that chromatic VEPs are abnormal in Down syndrome, and this may reflect abnormal processing of chromatic stimuli in this population. Alternatively, these abnormalities may arise due to abnormal cortical morphology, which may occur with normal or abnormal processing of chromatic signals. These findings further indicate that abnormality of chromatic VEPs may be expected in Down syndrome, and is not necessarily indicative of pathology or other abnormal function that is unrelated to the syndrome.

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Shawkat, Fatima Suham. "Pattern visual evoked potentials : comparison of onset, reversal and offset components." Thesis, University College London (University of London), 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.266482.

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McGlone, Laura. "Flash visual evoked potentials and early visual development in infants born to drug misusing mothers." Thesis, University of Glasgow, 2012. http://theses.gla.ac.uk/3184/.

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Background / Aims: Maternal drug misuse in pregnancy is a significant clinical and public health problem. Consequences for the newborn infant include prematurity, intrauterine growth restriction (IUGR) and neonatal abstinence syndrome (NAS). There is increasing evidence that maternal drug misuse in pregnancy may have longer term adverse effects on infant visual and neurodevelopmental outcome. Most of the evidence regarding visual outcomes in particular derives from small uncontrolled studies with a lack of adequately powered, controlled studies to date. The visual evoked potential (VEP) can be used to assess the integrity and maturity of the infant visual pathway and both visual and neurodevelopmental abnormalities can be predicted by abnormal VEPs in infancy. Drug misuse is also associated with alteration of the VEP in adults and in animal models. Many drugs used in pregnancy can cross the placenta and enter the fetal circulation, including illicit drugs and prescribed methadone, which is the currently recommended treatment for pregnant opiate-dependent women. Hitherto few studies have investigated the effects of maternal drug misuse upon the newborn infant VEP. This study investigates in detail the effects of prescribed methadone and additional illicit drug use in pregnancy upon the infant VEP recorded at birth and at six months of age, and explores any association with NAS. The range and incidence of visual and neurodevelopmental abnormalities at six months of age is described, and how these relate to a history of NAS and the pattern of in utero drug exposure is explored. Pilot work: Pilot work demonstrated the feasibility of recording neonatal flash VEPs in a small group of infants exposed to methadone in utero, and showed that drug exposed infants had abnormal VEPs compared to unmatched controls. A further pilot study described longer term visual outcomes, which included nystagmus, reduced visual acuity and strabismus, in a selected group of infants and children exposed to methadone in utero, thus informing clinical and electrophysiological assessment at six months of age. The pilot studies were followed by a major prospective cohort study. Prospective Study: One hundred and two term infants of mothers prescribed substitute methadone during pregnancy and 50 comparison infants matched for birth weight, gestation and socio-economic group were recruited in the neonatal period. Flash and flicker VEPs were recorded from the occipital scalp of infants within three days of birth. Drug exposure was determined by maternal history, maternal and infant urine and meconium toxicology. Excess alcohol exposure in utero was determined by elevated fatty acid ethyl esters in meconium. Neonatal flash VEPs were classified as mature, typical, or immature according to waveform morphology, and amplitude and latencies measured. Flicker VEPs were analysed using a fast-Fourier transformation and responses at each flicker frequency determined. The same cohort of drug-exposed and comparison infants was invited for clinical visual evaluation at six months of age in conjunction with pattern-onset VEPs and Griffiths developmental assessment. Results: Neonatal testing: Neonatal VEPs were successfully recorded from 100 drug-exposed infants and 50 matched comparison infants at a median age of 24 hours (IQR 13-44). Gestational age, birth weight and socio-economic group did not differ between groups. Flash VEPs from methadone-exposed infants had fewer P1 components (p=0.001), and were more likely to be of immature waveform (p<0.001) compared to comparisons. VEPs from methadone-exposed infants were also smaller in overall amplitude (median 27µV vs 39.5µV, p<0.001). The relative risk of an abnormal VEP in the methadone-exposed cohort was 5.6 with an attributable risk percent of 82%. The majority of infants were exposed to illicit drugs in addition to prescribed methadone, most commonly opiates (74%) and benzodiazepines (66%). VEPs did not differ between infants exposed to opiates only, those additionally exposed to benzodiazepines and those exposed to stimulants. Regression analysis confirmed that the difference in VEP parameters between drug-exposed and comparison infants was associated with methadone exposure and not other drugs of misuse. 48% of the methadone-exposed cohort developed NAS requiring pharmacological treatment; there was no association between neonatal VEPs and subsequent onset or severity of NAS. Flicker VEP analysis demonstrated an optimal flicker frequency of 4.6 Hz in both groups, but there were few differences in the proportion of responses between groups. Six month follow-up: Retention rate to six month follow-up was 79% for the methadone-exposed cohort and 52% for comparison infants. Age at assessment (median 27 weeks, range 26-30 wk), weight and OFC did not differ between groups. The demographic characteristics of comparison infants who were followed up were compared to those of comparison infants who were not followed up. There were no significant differences in birth weight (2 sample t-test p=0.445), OFC (2 sample t-test p=0.712), gestation (Mann-Whitney test p=0.984), 5-minute Apgar score (Mann-Whitney test p=0.263) or DEPCAT score (Mann-Whitney test p=0.258) between groups. Methadone-exposed infants were more likely to have visual abnormalities than comparison infants, even after correcting for excess in utero alcohol exposure (40% vs 8%; adjusted p=0.007). Abnormalities in the methadone-exposed cohort included nystagmus (11%), strabismus (25%) and reduced visual acuity (22%). The relative risk of an abnormal visual outcome in the methadone-exposed cohort was 5.1 with an attributable risk percent of 80%. Electrophysiological abnormalities persisted at six months of age: methadone- exposed infants had smaller amplitude pattern VEPs (25 μV vs 34 μV; p=0.005) with delayed peak latencies (115ms vs 99ms; p=0.019) and fewer responses at the small check size (p=0.003), compared to controls. Methadone-exposed infants had significantly lower neurodevelopmental scores compared to comparison infants (GQ 97 for cases vs 105 for controls; p<0.001), even after correcting for maternal smoking, antidepressant treatment and excess alcohol consumption during pregnancy. Infants exposed to poly-drug misuse and treated for NAS in the newborn period performed particularly poorly on their neurodevelopmental scores. Visual impairment was an independent predictor of poor neurodevelopmental outcome and most infants scoring <85 on neurodevelopmental assessment had co-existing visual problems. Conclusions: In utero exposure to prescribed methadone and other substances of misuse is associated with an alteration in visual electrophysiology in the newborn period suggestive of immature visual maturation. These changes are independent of additional benzodiazepine or stimulant exposure, and appear to be associated with prescribed substitute methadone. At six months of age, there is a high incidence of clinical visual abnormalities in infants exposed to methadone and other drugs of misuse in utero. Persistence of electrophysiological abnormalities beyond the neonatal period suggests that opiates may have a longer term effect on the developing visual system. Drug-exposed infants also have poorer neurodevelopmental scores than matched comparison infants after correcting for maternal smoking and excess alcohol intake. The bias of loss to follow-up was minimised by the high retention rate of drug-exposed infants. Although there was a higher loss of comparison infants, there were no differences in demographic characteristics between comparison infants followed up and those not followed up, suggesting the groups were similar. In addition, published data suggest the incidence of visual abnormalities described in the comparison population to be representative of the larger population.

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Flanagan, John G. "Automated assessment of visual fields and their inter-relation to evoked potentials in visual disorders." Thesis, Aston University, 1985. http://publications.aston.ac.uk/14594/.

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The Octopus Automated Perimeter was validated in a comparative study and found to offer many advantages in the assessment of the visual field. The visual evoked potential was investigated in an extensive study using a variety of stimulus parameters to simulate hemianopia and central visual field defects. The scalp topography was recorded topographically and a technique to compute the source derivation of the scalp potential was developed. This enabled clarification of the expected scalp distribution to half field stimulation using different electrode montages. The visual evoked potential following full field stimulation was found to be asymmetrical around the midline with a bias over the left occiput particularly when the foveal polar projections of the occipital cortex were preferentially stimulated. The half field response reflected the distribution asymmetry. Masking of the central 3° resulted in a response which was approximately symmetrical around the midline but there was no evidence of the PNP-complex. A method for visual field quantification was developed based on the neural representation of visual space (Drasdo and Peaston 1982) in an attempt to relate visual field depravation with the resultant visual evoked potentials. There was no form of simple, diffuse summation between the scalp potential and the cortical generators. It was, however, possible to quantify the degree of scalp potential attenuation for M-scaled full field stimuli. The results obtained from patients exhibiting pre-chiasmal lesions suggested that the PNP-complex is not scotomatous in nature but confirmed that it is most likely to be related to specific diseases (Harding and Crews 1982). There was a strong correlation between the percentage information loss of the visual field and the diagnostic value of the visual evoked potential in patients exhibiting chiasmal lesions.

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Highsmith, Jennifer Rea. "Changes in chromatic pattern-onset VEP with full-body inversion." abstract and full text PDF (free order & download UNR users only), 2007. http://0-gateway.proquest.com.innopac.library.unr.edu/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:1446433.

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Westerfield, Marissa Anne Navarrete. "The role of the cerebellum in visual spatial attention : an event-related potential study /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 1999. http://wwwlib.umi.com/cr/ucsd/fullcit?p9952646.

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Beneish, Raquel Gabriela. "Pattern reversal visual evoked potentials in children with strabismic and with anisometropic amblyopia." Thesis, McGill University, 1988. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=61883.

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Gembler, Felix [Verfasser]. "Parameter Optimization for Brain-Computer Interfaces based on Visual Evoked Potentials / Felix Gembler." Bielefeld : Universitätsbibliothek Bielefeld, 2020. http://d-nb.info/1222672227/34.

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Beveridge, Ryan. "An assessment of factors influencing neurogaming with motion-onset visual evoked potentials (mVEPs)." Thesis, Ulster University, 2018. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.736777.

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Brain-computer interface (BCI) technology offers movement-independent control of computer applications by translating cortical activity into semantic control signals for a computer to execute. One prominent application of BCI technology is brain-computer games interfacing (BCGI) or neurogaming. This thesis aimed to advance the field of neurogaming and is an account of the work conducted whilst investigating the feasibility of employing motion-onset visual evoked potentials (mVEPs) for control in a range of neurogames and the factors that influence performance when employing such a control strategy. mVEPs manifest near the visual cortex when motion-related stimuli are attended to visually and therefore are likely to be elicited naturally by games graphics scenes and the motions of in-game objects. There are limited studies investigating the potential for mixing games graphics with visual motion-based stimuli to elicit mVEPs for control in games. This thesis addresses this lacuna and improves our understanding of the factors that influence neurogaming with mVEPs. Firstly, participants were presented with mVEP-inducing stimuli overlaid on games graphics of varying complexity. Offline analysis of the EEG indicated that there was some correlation between graphical complexity and mVEP detection performance but the differences were insignificant for moderate variations in graphical complexity. Another offline study involved mVEP stimuli mixed with five different commercially available video games - each representing different graphical complexities, genre, and generation of gaming console. A 3D fast-paced car-racing game consistently provided the greatest mVEP detection accuracies. To validate the use of a virtual reality (VR)-based display modality, two different game level presentations, based on the car-racing genre were studied - one with rudimentary and one with highly detailed graphics. Offline results indicated that mVEP detection accuracy provided by the Oculus Rift VR headset did not differ to an LCD computer display, demonstrating the possibility of employing contemporary display technologies in neurogaming. Once we established that mVEPs could be detected with graphics of varying complexity and that perhaps the car-racing genre is best suited for mVEP-based control, a series of online control experiments with a mVEP-controlled 3D car-racing game were conducted comparing the performance of adults to teenagers, a relatively understudied age group in neurogaming. We investigated user performance based on different lap speeds dictated by the number of event-related potentials (ERPs) averaged to make a game control decision. Our findings indicate that adult participants outperformed their teenage counterparts and that mVEP detection is robust to variations in the setup of the signal processing and system calibration. In summary, this thesis has implications for BCI control strategies involving mVEPs, gameplay quality, speed of control, performance assessment and calibrating mVEP-based BCIs. A broad range of users, including teenagers, have been evaluated in a mVEP-based neurogaming study for the first time.

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Siegel, Lance Mitchell. "The Analysis of 3-Channel "Vector" Visual Evoked Potentials and Possible Neuroanatomical Correlates." VCU Scholars Compass, 1990. http://scholarscompass.vcu.edu/etd/5102.

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he use of evoked potentials to evaluate the functional integrity of neuronal pathways has become a useful and accepted practice in clinical medicine. The use of visual evoked potentials for assisting in the diagnosis of such diseases as optic neuritis and multiple sclerosis is also well recognized. However, the visual evoked potential, unlike the auditory evoked potentials, lacks a well deﬁned electrophysiological to neuroanatomical correlation; especially that of a signiﬁcant non-cortical component. Currently, visual evoked potentials rely principally on the measurement of a cortical (occipital) positive peak of activity at 100ms (P100), recorded with a single channel electrode system, to evaluate pathway integrity. In this study, visual evoked potentials were recorded using a three-channel, orthogonal co-ordinate system which we have designated "vector" visual evoked potentials (VVEP). This method allows the generated evoked response to be plotted on a three dimensional co-ordinate system with respect to time. Through the use of pattern reversal of a checkerboard pattern, in full and hemi retinal ﬁeld stimulation, reproducible activity both prior to and aﬁer the P100 wave was demonstrated. In particular, activity found at approximately 55ms is believed to be generated from the Lateral Geniculate Body. Furthermore, because this method summarizes the activity of the entire brain for a given time, as opposed to the single channel recording, a great deal of information about the entire visual pathway can be suggested. Finally, anatomical correlates to discrete activities identiﬁed by this method can be made.

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Doran, Matthew M. "The role of visual attention in multiple object tracking evidence from ERPS." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file, 110 p, 2009. http://proquest.umi.com/pqdweb?did=1885675151&sid=5&Fmt=2&clientId=8331&RQT=309&VName=PQD.

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Camargo, Marina von Zuben de Arruda. "Propriedades espaço-temporais da acuidade vernier no córtex visual humano usando potenciais visuais provocados de varredura." Universidade de São Paulo, 2012. http://www.teses.usp.br/teses/disponiveis/47/47135/tde-12062012-160008/.

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Esta pesquisa pretendia estabelecer um mapa espaço temporal das respostas de vernier no córtex visual humano. O uso do potencial visual provocado de varredura (PVPv) proporciona medidas eficientes e sensíveis dos limiares de vernier com os quais se pode começar a examinar as respostas corticais de vernier no âmbito dos parâmetros espaço temporais. As respostas de vernier foram avaliadas em relação à hipótese de que os sinais retinianos provenientes das células ganglionares da via magnocelular e não da via parvocelular compõem o input neural para córtex que é utilizado para gerar as respostas de vernier (tarefas de localização de alta precisão Lee et a., 1990; Lee et al., 1995). Métodos: As respostas de vernier no córtex humano foram medidas por meio do potencial visual provocado de varredura (PVPv). Quebras de vernier foram introduzidas em grades de ondas quadradas de produzindo colunas verticais intercaladas de barras estáticas e móveis. Medidas binoculares da acuidade vernier foram feitas em grades de alto contraste (64%) em função de 3 frequências temporais (3, 6 e 15 Hz) e 2 frequências espaciais (1 e 8 c/g). Medidas utilizando grades de baixo contraste foram feitas em função de 3 frequências temporais (3, 6 e 10Hz) e 3 frequências espaciais (1, 2 e 8c/g) em ambos os protocolos (alto e baixo contraste) as medidas foram feitas utilizando o PVPv. Foi utilizado o sistema POWER DIVA que utiliza a metodologia dos mínimos quadrados recursivos para extrair a amplitude e fase da resposta nos harmônicos selecionados da frequência do estímulo. Foram analisados o primeiro (1F1) e o segundo (2F1) harmônicos neste estudo. Com base em estudos anteriores, assume-se que o primeiro componente harmônico refere-se às respostas ao estímulo de vernier, e o segundo às respostas ao movimento relativo dos elementos do estímulo. Esta hipótese foi testada por meio da utilização de protocolos controle para ambos os arranjos de estímulos (alto e baixo contraste) em que foram utilizados os mesmos parâmetros, porém com deslocamentos entre as barras completamente simétricos (elementos da grade jamais se alinhavam). O sistema POWER DIVA calcula para cada segundo de janela de análise (bin) a amplitude local. A amplitude média do ruído nos 10 bins de análise é utilizada para calcular a razão sinal ruído para cada bin. Apenas sinais com razão sinal ruído maior que 3 foram considerados resposta. A média vetorial de 8 tentativas para cada condição de estímulo foi utilizada para determinar os limiares.Resultados: Os dados são consistentes com dados psicofísicos anteriores, especialmente os dados de Bradley & Skottun (1987) que demonstraram decréscimo significativo nos limiares de vernier com o aumento da frequência espacial. Os limiares eletrofisiológicos de vernier obtidos com o presente trabalho mostraram-se paralelos aos dados psicofísicos em função das frequências espaciais em ambos os protocolos. Os limiares no 1F1 também demonstraram redução significativa com o aumento da frequência temporal em altas frequências espaciais
The research was directed at establishing a spatiotemporal map of human cortical vernier responses. The use of swept-parameter, steady state visual evoked potential (sweep VEP, or sVEP) provides efficient and sensitive measurement of vernier thresholds with which to begin to examine cortical vernier responses over the spatio-temporal parameter space. The vernier responses were evaluated in relation to the hypothesis that the magnocellular (M) but not parvocellular (P) ganglion cell retinal output forms the neural input to cortex that is used to derive vernier (high precision localization task - Lee et al., 1990; Lee et al., 1995). Methods: Human cortical vernier responses were measured using the sweep visual evoked potential (sVEP). Vernier offsets are introduced into a square wave grating producing interleaved vertical columns of moving and static bars. Binocular measurements of the vernier acuity were made using high contrast (64%) gratings as a function of 3 temporal frequencies (TF = 3, 6 and 15 Hz) and 2 spatial frequencies (SF = 1 and 8 c/g). Measurements were also made at low contrast (8%) as a function of 3 temporal frequencies (3, 6 and 10Hz) and 3 spatial frequencies (1, 2 and 8c/g) using the sVEP. The POWER DIVA system uses the recursive least squares to extract the response amplitude and phase at selected harmonics of the stimulus frequency. We analyzed the evoked potentials at the first (1F1 fundamental) and second (2F1) harmonics. Based on prior research, we take the 1F1 component to be the specific response to the periodic vernier onset/offset, while the 2F1 component reflects local relative motion responses. We checked this assumption by also measuring sVEPs using a motion control protocol in which equivalent displacement amplitudes were presented in and identical stimulus array, but with the displacements being completely symmetrical alternations between two states of misalignment (grating elements were never aligned). To ensure that the amplitude data used for the regression and extrapolation to threshold is really a response to stimulus instead of noise, POWER DIVA calculates, for each 1-second analysis window (time bin), a local noise amplitude. The mean noise amplitude across 10 analysis bins is used to calculate the signal to noise ratio for each time bin. Only signals with a signal to noise ratio > 3 were considered as a response. The vector average of at least 8 trials was used to determine thresholds. Results: The data are consistent with some comparable prior psychophysical data, especially data from Bradley & Skottun (1987) who showed significant decrease in the vernier thresholds with the increase of spatial frequency. Our cortical (sVEP) vernier thresholds paralleled the psychophysical data as a function of SF in both protocols. The 1F1 (vernier) thresholds also exhibited a significant decrease with increase of temporal frequency at high SF

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Lai, Sui-man, and 賴萃文. "Design of a time-encoded visual stimulation method for brain computer interface based on chromatic transient visual evoked potentials." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2009. http://hub.hku.hk/bib/B43085829.

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Lai, Sui-man. "Design of a time-encoded visual stimulation method for brain computer interface based on chromatic transient visual evoked potentials." Click to view the E-thesis via HKUTO, 2009. http://sunzi.lib.hku.hk/hkuto/record/B43085829.

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Padhiar, Sanjita. "Study of the cholinergic factors affecting the flash and pattern reversal visual evoked potentials." Thesis, Aston University, 1993. http://publications.aston.ac.uk/14601/.

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The effects of cholinergic agents undergoing clinical trials for the treatment of Alzheimer's disease and the anticholinergic agent scopolamine, were investigated on the components of the flash and pattern reversal visual evoked potentials (VEPs) in young healthy volunteers. The effect of recording the flash and pattern reversal VEPs for 13 hours in 5 healthy male volunteers, revealed no statistically significant change in the latency or amplitude measures. Administration of the muscarinic agonist SDZ 210-086 to 16 healthy male volunteers resulted in the reduction of the flash N2-P2 and pattern reversal N75-P100 peak-to-peak amplitudes. These effects on the flash VEP occurred at both doses (0.5 and 1.0 mg/day), but only at the higher dose on the pattern reversal VEP. Administration of the antimuscarinic agent scopolamine to 11 healthy young male volunteers, resulted in a delay of the flash P2 latency but no effect on the pattern reversal P100 latency. The pattern reversal N75-P100 peak-to-peak amplitude was also increased post dosing. The combination of scopolamine with the acetylcholinesterase inhibitor SDZ ENA 713 resulted in no significant effect on the flash and pattern reversal VEPs, suggesting that the effects of scopolamine may have been partially reversed. Topical application of scopolamine in 6 young healthy volunteers also resulted in no statistically significant effects on the flash and pattern reversal VEPs. The selective effect of scopolamine on the flash P2 latency but not on the pattern reversal P100 latency, provided a model whereby new cholinergic agents developed for the treatment of Alzheimer's disease can be investigated on a physiological basis. In addition, the results of this study led to the hypothesis that the selective flash P2 delay in Alzheimer's disease was probably due to a cholinergic deficit in both the tectal pathway from the retina to the visual cortex and the magnocellular path of the geniculostriate pathway, whereas the lack of an effect on the pattern reversal P100 component was probably due to a sparing of the parvocellular geniculostriate pathway.

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Nagle, Mark. "The association between glycated haemoglobin levels and P100 visual evoked potentials in diabetes mellitus." Thesis, Aston University, 2016. http://publications.aston.ac.uk/28805/.

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Diabetes mellitus (DM) is a metabolic disorder which is characterised by hyperglycaemia resulting from defects in insulin secretion, insulin action or both. The long-term specific effects of DM include the development of retinopathy, nephropathy and neuropathy. Cardiac disease, peripheral arterial and cerebrovascular disease are also known to be linked with DM. Type 1 diabetes mellitus (T1DM) accounts for approximately 10% of all individuals with DM, and insulin therapy is the only available treatment. Type 2 diabetes mellitus (T2DM) accounts for 90% of all individuals with DM. Diet, exercise, oral hypoglycaemic agents and occasionally exogenous insulin are used to manage T2DM. The diagnosis of DM is made where the glycated haemoglobin (HbA1c) percentage is greater than 6.5%. Pattern-reversal visual evoked potential (PVEP) testing is an objective means of evaluating impulse conduction along the central nervous pathways. Increased peak time of the visual P100 waveform is an expression of structural damage at the level of myelinated optic nerve fibres. This was an observational cross sectional study. The participants were grouped into two phases. Phase 1, the control group, consisted of 30 healthy non-diabetic participants. Phase 2 comprised of 104 diabetic participants of whom 52 had an HbA1c greater than 10% (poorly controlled DM) and 52 whose HbA1c was 10% and less (moderately controlled DM). The aim of this study was to firstly observe the possible association between glycated haemoglobin levels and P100 peak time of pattern-reversal visual evoked potentials (PVEPs) in DM. Secondly, to assess whether the central nervous system (CNS) and in particular visual function is affected by type and/or duration of DM. The cut-off values to define P100 peak time delay was calculated as the mean P100 peak time plus 2.5 X standard deviations as measured for the non-diabetic control group, and were 110.64 ms for the right eye. The proportion of delayed P100 peak time amounted to 38.5% for both diabetic groups, thus the poorly controlled group (HbA1c > 10%) did not pose an increased risk for delayed P100 peak time, relative to the moderately controlled group (HbA1c ≤ 10%). The P100 PVEP results for this study, do however, reflect significant delay (p < 0.001) of the DM group as compared to the non-diabetic group; thus, subclincal neuropathy of the CNS occurs in 38.5% of cases. The duration of DM and type of DM had no influence on the P100 peak time measurements.

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Wong, Chi Man. "Phase information enhanced steady-state visual evoked potential-based brain-computer interface." Thesis, University of Macau, 2011. http://umaclib3.umac.mo/record=b2493316.

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Schenk, Eric R. "Detection of specific steady-state visual evoked potentials when multiple frequencies are available for stimulation." Ohio : Ohio University, 1998. http://www.ohiolink.edu/etd/view.cgi?ohiou1176401258.

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Pinsanor, Preeyanun. "Insamling av referensvärden för Visual evoked potentials (VEP) hos friska individer vid Centralsjukhuset i Karlstad." Thesis, Örebro universitet, Institutionen för hälsovetenskaper, 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:oru:diva-69415.

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Nordin, Henni. "Jämförelse av avstånd mellan bildskärm och patient genom analys av latens vid Visual Evoked Potentials." Thesis, Umeå universitet, Biomedicinsk laboratorievetenskap, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-185413.

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Schenk, Eric R. "Detection of specific steady-state visual evoked potentials when multiple frequencies are available for simulation." Ohio University / OhioLINK, 1998. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1176401258.

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Burton, Pamela Ann. "Physiological evidence of interactive object-based and space-based attention mechanisms." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file 50.79Mb,139 p, 2005. http://wwwlib.umi.com/dissertations/fullcit/3157279.

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Pereira, Silvana Alves. "Avaliação da acuidade visual em crianças com hidrocefalia : um estudo eletrofisiológico por potencial visual evocado de varredura." Universidade de São Paulo, 2008. http://www.teses.usp.br/teses/disponiveis/47/47135/tde-10062008-105554/.

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O objetivo do estudo foi medir a acuidade visual (AV) em crianças com diagnóstico de hidrocefalia, apresentando ou não a válvula de derivação ventricular (DVP). Participaram da pesquisa um total de 55 crianças (34 F e 21M) com diagnóstico de hidrocefalia (45 com DVP e 10 sem DVP), com idade entre zero a 291 semanas (média 74 semanas). A AV foi medida pela técnica do Potencial Visual Evocado de Varredura e os resultados foram comparados a valores de referência (Norcia, 1985b). Os diagnósticos etiológicos que levaram à hidrocefalia foram: hemorragia intracraniana (25 crianças), mielomeningocele (20 crianças) e hidrocefalia congênita (10 crianças). O diagnóstico de hidrocefalia foi estabelecido em média no 16° dia de vida. Verificamos que, 31 crianças tiveram o procedimento realizado com menos de 15 dias do diagnóstico de hidrocefalia enquanto que em 14 a válvula foi instalada após 15 dias. Das 55 crianças avaliadas no 1° exame, 18 fizeram o 2° exame, 13 fizeram o 3° exame, 10 completaram quatro exames e apenas cinco completaram as cinco avaliações. Os resultados mostram que dentre as 101 avaliações de AV realizadas em todas as crianças, 95 exames (94%) se mostraram alterados e seis normais. Não há diferença estatística entre a AV das crianças sem derivação em comparação com aquelas crianças cuja DVP foi realizada com tempo de derivação maior que 15 dias (p = 0.699). Houve, todavia, uma diferença estatística na AV, quando comparamos as crianças, cujas derivações foram realizadas em até 15 dias do diagnóstico da hidrocefalia, com aquelas cuja derivação foi realizada após 15 dias (p = 0.038) ou com aquelas que não foram derivadas (p = 0.031). Crianças que não tiveram complicações na DVP tiveram um melhor resultado de AV quando comparado com o grupo com complicação (p = 0.0001). No grupo de crianças com complicação, novamente aquelas que foram derivadas com tempo inferior a 15 dias do diagnóstico da hidrocefalia apresentou melhores resultados de AV quando comparado com aquelas crianças com complicação cuja derivação foi realizada com mais de 15 dias (p = 0.029). Nós concluímos que é possível a medida da acuidade visual de resolução pelos PVEs de varredura em crianças com diagnóstico de hidrocefalia e os valores geralmente são piores comparando aos valores normativos. O tempo da derivação e o número de complicações decorrentes da DVP parecem interferir nesta diferença. Em nosso conhecimento, este foi o primeiro trabalho a avaliar progressivamente, a acuidade visual de crianças, nos primeiros anos de vida, com hidrocefalia, com ou sem DVP e correlacionar o resultado com o tempo de derivações e número de complicações. Apesar da grande evolução tecnológica alcançada pela oftalmologia, ainda não somos capazes de prevenir as alterações visuais detectáveis pelo simples exame de AV nas crianças com hidrocefalia. O tempo para a inserção da válvula de derivação e o tratamento para as complicações ainda são medidas retardadas devido à prematuridade, instabilidade hemodinâmica e a não autorização do familiar. Estes motivos podem comprometer o desenvolvimento visual destas crianças.
The objective was to measure the visual acuity (VA) of children with the diagnosis of hydrocephalus with or without peritoneal-ventricular shunt (PVS). A total of 55 children with the diagnosis of hydrocephalus (45 with PVS and 10 without PVS) were included in the study (34F and 21M), with an age range of 0 to 291 weeks (mean=74 weeks). The VA was measured by the sweep visual evoked potential technique and the results were compared with reference values proposed by Norcia (1985b). Etiological diagnosis of the hydrocephalus was as follows: intracranial hemorrhage (25 children), meningomyelocele (20 children) and congenital hydrocephalus (10 children). The diagnosis of hydrocephalus was made in an average time of 16 days of life. After the diagnosis, the insertion of the PVS, when made, was accomplished in average on the 16th day. Of those with a PVS, in 31 the ventricular valve was inserted before 15 days after the diagnosis whereas in 14 in shunt was inserted after 15 days. Of the 55 children evaluated in the first exam, 18 were evaluated in a second exam, 13 did the third exam, 10 completed 4 exams and only 5 completed the 5 evaluations. The results of the 101 sweep visual evoked potential performed in all children, 95 exams (94%) were abnormal and only 6 were normal. There was no statistical difference in the VA of children without a ventricular shunt in comparison with those in which the shunt was inserted after 15 days of the diagnosis of hydrocephalus (p=0.699). There was, however, a statistical difference in the VA between children with a ventricular shunt inserted before 15 days of the diagnosis and children with a ventricular shunt after 15 days (p=0.038) or those without a shunt (p=0.031). Children with no complications of the ventricular shunt had a better VA as compared to those with shunt complications (p= 0.0001). In the group of children with complications, again those who had a shunt inserted before 15 days bad better VA results in comparison to those in whom the shunt was inserted after 15days (p=0.029). We concluded that measuring visual acuity by sweep visual evoked potential is feasible in children with the diagnosis of hydrocephalus and that results are usually worse comparing with reference values. The timing for insertion of a ventricular shunt and the occurrence of complications of this procedure are factors that may influence the VA. To our knowledge, this is the first study that progressively evaluated the VA in children, of early age, with hydrocephalus, with or without a ventricular shunt and correlated the VA with the timing and complications of the ventricular shunt. Despite the great technological advance in ophthalmology, we are still unable to prevent visual impairments, detectable by simple visual acuity tests, in children with hydrocephalus. The timing of the insertion of the ventricular shunt and the adequate treatment of the potential complications may be delayed due to prematurity, hemodynamic instability and family refusal. This delay may compromise the visual development of these children.

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Carmona, Francisco Manuel Moreno. "Desenvolvimento da acuidade visual de resolução de grades de cães da raça terrier brasileiro pelo método do potencial visual evocado de varredura." Universidade de São Paulo, 2004. http://www.teses.usp.br/teses/disponiveis/10/10137/tde-11072007-090535/.

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O objetivo deste trabalho foi medir o desenvolvimento da acuidade visual (AV) de resolução de grades de filhotes de cães da raça Terrier Brasileiro utilizando-se o método do potencial visual evocado de varredura (PVEV). Foram mensuradas as AVs de resolução de grades de 18 cães da raça Terrier Brasileiro, 14 filhotes (8 machos e 6 fêmeas), de duas ninhadas diferentes e 4 adultos (2 machos e 2 fêmeas, incluindo-se a matriz). Os PVEVs (NuDiva) foram registrados a partir de dois eletrodos ativos posicionados no escalpo em O1 e O2, um eletrodo referência posicionado em OZ e um eletrodo terra em CZ. O estímulo consistiu de padrões reversos de grades de ondas quadradas a uma freqüência de 6 Hz, variando de 0,2 a 12 ciclos por grau (cpg). A luminância média do monitor foi de 159.3 cd/m2. As AVs foram medidas semanalmente a partir da 4ª semana de vida até a 13ª semana. A distância de teste foi de 50 cm e o animal permaneceu no colo de seu acompanhante, com a cabeça suavemente contida para manter os olhos voltados ao estímulo do monitor de vídeo (Dotronix D788). O teste foi realizado em sala escura sem o uso de midriáticos, sedativos ou anestésicos. A mediana da AV dos filhotes variou de 2,28 cpg (Q2= 2,12; Q3= 2,36) (equivalente a 20/265 na escala de Snellen) na 4ª semana para 9,18 cpg (Q2= 8,64; Q3= 9,31) (20/65) na 13ª semana. A mediana de AV dos cães adultos foi de 8,82 cpg (Q2= 8,71; Q3= 8,94) (20/70). Este valor foi atingido pelos filhotes ao redor da 10ª semana. A AV aumentou rapidamente até, aproximadamente, a 7ª semana. Um crescimento mais moderado foi observado até a semana 9. A taxa de crescimento declinou gradualmente a partir da 10ª semana. A partir daí os valores de AV praticamente estabilizam ao redor de 20/65 (χ2 = 120,61; p < 0.001). Houve uma diferença estatisticamente significante das AVs a cada quatro semanas (Dunn\'s Method; p< 0,05). Houve uma alta correlação positiva entre a AV e o peso dos animais (R= 0,83; p< 0,001; Spearman Rank Order Correlation). O PVE de varredura é método não invasivo que permite mensurar a AV de forma precisa, sem requerer excessiva cooperação e atenção, na população alvo. O método tem aplicação clínica e investigativa, não sendo necessário o uso de cicloplégicos ou de contenção química. Os filhotes atingiram os valores de acuidade semelhantes aos de adultos na 10ª semana de vida. A AV dos adultos examinados (20/70) está de acordo com estimativas encontradas em outros estudos. A acuidade visual de cães da raça Terrier Brasileiro está entre 8,60 cpg (20/70) e 9,57 cpg (20/60).
Our aim in this study was to measure the development of grating visual acuity (VA) in Brazilian Terrier puppies by sweep visual evoked potentials (sVEP). Grating VAs of 18 Brazilian Terrier dogs, 14 puppies (8 male, 6 female), from two different litters and 4 adults (2 male, 2 female), including the matrix, were measured. Sweep-VEPs (NuDiva) were recorded from two active electrodes placed on the scalp at O1 and O2, a reference electrode at Oz and a ground electrode at Cz. The stimuli were pattern reversal square wave gratings at a rate of 6 Hz, ranging from 0.2 to 12 cycles per degree (cpd). The mean monitor luminance was 159.3 cd/m2. The VAs were measured weekly from the 4th to the 13th week. Viewing distance was 50cm and the pup was positioned on the lap of the investigator with the head gently supported to maintain the eyes in front of the video monitor (Dotronix D788). The test was performed in a darkened room without mydriatic, sedative or anesthetic drugs. The median VA ranged from 2.28 cpd (Q2= 2.12; Q3= 2.36) (equivalent to 20/265 Snellen VA) at the 4th week to 9.18 cpd (Q2= 8.64; Q3= 9.31) (20/65) at the 13th week. The median of adult VA was 8.82 cpd (Q2= 8.71; Q3= 8.94) (20/70). This value was reached by the puppies around the 10th week. VA increase was steeper up to the 7th week than afterwards. The rate of increase gradually declined up to the 10th week (χ2= 120.61; p< 0.001). The VAs were statistically different witch four week (Dunn\'s Method; p< 0.05). There was a high positive correlation between the VA and body weight (R= 0.83; p< 0.001; Spearman Rank Order Correlation). The Sweep-VEP method offers a rapid and reliable procedure for the quantification of grating VA in puppies and adults dogs, without the need for sedation. Pup VA reached adult values at the 10th week of life. The mean of adult VA measured (20/70) is in accordance with estimates of VA of dogs in other studies. The range of VA of Brazilian Terrier dogs were 8.60 cpd (20/70) to 9.57 cpd (20/60).

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Arctaedius, Jenny. "Processing of task-irrelevant sounds while performing a visual task : A study of auditory steady-state evoked potentials." Thesis, Stockholms universitet, Psykologiska institutionen, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-180695.

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Perceptual capacity and selection in attention have for long been an interest in cognitive science, with early theories of early selection to late selection. Hearing is an important subject to investigate when it comes to attention and early auditory processing can be investigated by using auditory steady state responses (ASSRs). Studies on ASSRs to irrelevant sounds have investigated the 40 Hz ASSR and concluded no effect of load. As studies on temporal activation of ASSRs indicate that lower and higher frequencies activate different stages of the auditory pathway, there is a need to investigate other frequencies than the 40 Hz. This study investigated the 20 Hz and 80 Hz amplitude modulations using EEG. The visual stimuli were a rapid stream of letters and varied between no load, low load, and high load. The auditory stimuli were an amplitude-modulated tone with a carrier frequency of 500 Hz, with three varying modulation frequencies: 20 Hz, 40 Hz, and 80 Hz. Load level and amplitude modulation alternated over 18 blocks. The statistical analysis was comprised of t tests and Bayes Factor. Results provided support for the null hypothesis for the 20 Hz frequency but were inconclusive for the 40 Hz and 80 Hz frequency. More data is needed to give a conclusion for effect of load for the 40 Hz and 80 Hz frequency. As we did not have enough data, we cannot say anything about the temporal activation of ASSRs in the brain.

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Challa, Naveen K. "An electrophysiological study of chromatic processing in the human visual system. Using visual evoked potentials and electroretinograms to study cortical and retinal contributions to human trichromatic vision." Thesis, University of Bradford, 2011. http://hdl.handle.net/10454/5343.

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The work in this thesis is concerned with examining the retinal and cortical contributions to human trichromatic colour vision. Chromatic processing at the cortex level was examined using visual evoked potentials (VEPs). These responses were elicited by chromatic spot stimuli, which were manipulated in order to selectively activate the chromatic processing system. Chromatic processing at the retinal level was examined using the electroretinograms (ERGs) for which cone isolating stimuli were used to assess the nature of L and M cone inputs to cone-opponent mechanisms. The results from the VEP experiments suggest VEP morphology is dependent upon 1) chromatic and or luminance contrast content of the stimulus, 2) stimulus size, and 3) extent to which the chromatic stimulus activates either the L/M or S/(L+M) opponent mechanism. The experiments indicate that chromatic stimulation is indexed by large N1 component and small offset responses. Optimal stimulus size for chromatic isolation is 2-4 ° along L/M axes and 6° along S/(L+M) axis. From the ERG experiments, It has been shown that the low (12Hz) and high (30Hz) temporal frequency flickering stimuli can isolate the chromatic and luminance processing mechanisms in the retina. For low temporal frequency ERGs, the L:M ratio was close to unity and L/M phase difference was close to 180°. For high temporal frequency ERGs, the L:M ratio was more than unity and L/M phase difference was close to 90°. In addition to this, the variation in L:M ratio across the retinal eccentricity was also examined. These results suggest, for the chromatic processing, L:M ratio is close to unity independent of retinal eccentricity and individuals. For the luminance processing, L:M ratio is more than unity and depends upon the region of the retina being stimulated. These findings indicate the maintenance of cone selective input for the chromatic processing across the human retina.

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Walker, Pamela M. "Own- versus other-race face perception : social contact and the human brain." Thesis, University of Oxford, 2006. http://ora.ox.ac.uk/objects/uuid:2d79e338-7197-40e4-a9d5-94d160125c45.

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The experiments in this thesis used behavioural measures and event-related potentials (ERPs) to investigate the influence of race on face processing in the brain. Previous behavioural research has highlighted an own-race effect in face processing, whereby individuals are more accurate at recognizing own-race compared to other-race faces. The current Thesis examined the own-race effect at perceptual and neural levels. Social influences on the own-race effect were also investigated, such as other-race experience, anxiety and implicit social bias, as these may account for differential own- versus other-race face processing. The main aim of the experiments contained in this thesis was to delve deeper into the examination of own and other-race face perception through a series of original experiments. Participants performed a variety of perceptual discrimination and identification tasks, and completed measures of explicit other-race experience and implicit racial bias to record their perceptions of other-race individuals. Chapters 2-4 saw the development of a new paradigm that tested the own-race effect in perception, in contrast to traditional recognition memory investigations. In Chapter 2 the own-race effect was investigated developmentally and found across three age-groups, and was larger in the two older age-groups. Chapters 3 and 4 found that the own-race effect differed across racial groups, and that social variables such as other-race experience influenced the strength of the own-race effect. In the latter experimental chapters, ERPs revealed that the behavioural own-race effect was evident at a neural level. Chapter 7 demonstrated that face-related stages of processing in the brain were sensitive to race of face. In Chapters 8 and 9, the sensitivity of face processing to own and other-race emotional expression processing was also examined. The additional social factor of emotional expression was explored in order to further the investigation of socially relevant information processing from the face. Findings from the last two experimental chapters demonstrated differential emotional face processing for own- versus other-race faces. Confirming the findings of the behavioural experiments, own- versus other-race emotion processing varied across racial groups and was subject to social influences such as other-race experience, intergroup anxiety and implicit racial bias. Overall, behavioural and neural investigations of the own-race effect demonstrated the influence of social variables such as other-race experience, intergroup anxiety and implicit racial bias on the way in which individuals processed own- versus other-race faces in the human brain.

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Gaume, Antoine. "Towards cognitive brain-computer interfaces : real-time monitoring of visual processing and control using electroencephalography." Thesis, Paris 6, 2016. http://www.theses.fr/2016PA066137/document.

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Les interfaces cerveau-machine (ICM) ouvrent des voies de communication alternatives entre le cerveau et son environnement. Elles peuvent être utilisées pour supplanter une fonction biologique défaillante ou pour permettre de nouveaux modes d’interaction à l’utilisateur. Les ICM de sortie, dont le fonctionnement se base sur la lecture de données biologiques, nécessitent la mesure de signaux de contrôle stables dans le temps et dans la population. La recherche de tels signaux et leur calibration sont des étapes clefs dans la conception d’une ICM. Cette étude s’intéresse en premier lieu aux ICM utilisant les potentiels évoqués visuels comme signaux de contrôle. Un modèle est proposé pour la prédiction individuelle de ces potentiels en régime permanent, c’est-à-dire lorsqu'ils sont issus d’une stimulation périodique. Ce modèle utilise une sommation linéaire corrigée en amplitude de la réponse à des stimulations visuelles discrètes pour prédire quantitativement la nature et la localisation spatiale de la réponse à des stimulations répétées. Les signaux modélisés sont ensuite utilisés en temps réel comme base de comparaison pour décoder les signaux électroencéphalographiques d’une ICM. Dans une deuxième partie, un paradigme est proposé pour le développement d’ICM cognitives, c’est-à-dire permettant la mesure de fonctions cérébrales de haut niveau. L’originalité du paradigme réside dans la volonté de mesurer la cognition en continu plutôt que son influence sur des événements discrets. Une expérience visant à discriminer différents états d’attention visuelle soutenue est proposée, avec l’ambition d’une mesure en temps réel pour le développement de systèmes de neurofeedback
Brain-computer interfaces (BCIs) offer alternative communication pathways between the brain and its environment. They can be used to replace a defective biological function or to provide the user with new ways of interaction. Output BCIs, which are based on the reading of biological data, require the measurement of control signals as stable as possible in time and in the population. Identification and calibration of such signals are crucial steps in the conception of a BCI.The first part of this study focuses on BCIs using visual evoked potentials (VEPs) as control signals. A model is proposed to predict steady-state VEPs individually, i.e. to predict the response of a given subject’s brain to periodic visual stimulations. This model uses a linear summation of transient VEPs and an amplitude correction for quantitative prediction of the shape and spatial organization of the brain response to repeated stimulations. The simulated signals are then used as a basis of comparison for real-time decoding of electroencephalographic signals in a BCI.In the second part of this study, a paradigm is proposed for the development of cognitive BCIs, i.e. for the real-time measuring of high-level brain functions. The originality of the paradigm lies in the fact that correlates of cognition are measured continuously, instead of being observed on discrete events. An experiment with the purpose of discriminating between several levels of sustained visual attention is proposed, with the ambition of real-time measurement for the development of neurofeedback systems

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Johansson, Björn. "A study of some temporal properties of the human visual evoked potential, and their relation to binocular function /." Linköping : Linköping University, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-7584.

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Palladino, G., S. Loizzo, A. Fortuna, S. Canterini, F. Palombi, R. P. Erickson, F. Mangia, and M. T. Fiorenza. "Visual evoked potentials of Niemann-Pick type C1 mice reveal an impairment of the visual pathway that is rescued by 2-hydroxypropyl-ẞ-cyclodextrin." BioMed Central, 2015. http://hdl.handle.net/10150/610327.

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BACKGROUND: The lysosomal storage disorder, Niemann Pick type C1 (NPC1), presents a variable phenotype including neurovisceral and neurological symptoms. 2-Hydroxypropyl-ss-cyclodextrin (HPssCD)-based therapies are presently the most promising route of intervention. While severe cerebellar dysfunction remains the main disabling feature of NPC1, sensory functions including auditory and olfactory ones are also affected. Morphological and functional anomalies of Npc1 (-/-) mouse retina have also been observed, although the functional integrity of the visual pathway from retina to visual cortex is still unsettled. We have addressed this issue by characterizing the visual evoked potential (VEP) response of Npc1 (-/-) mice and determining if/how HPssCD administration influences the VEPs of both Npc1 (-/-) and Npc1 (+/+) mice. METHODS: VEP elicited by a brief visual stimulus were recorded from the scalp overlying the visual cortex of adult (PN, postnatal days 60, 75, 85 and 100) Npc1 (+/+) and Npc1 (-/-) mice that had received repeated injections of either HPssCD or plain vehicle. The first injection was given at PN4 and was followed by a second one at PN7 and thereafter by weekly injections up to PN49. Cholesterol accumulation and myelin loss were finally assessed by filipin staining and myelin basic protein immunohistochemistry, respectively. RESULTS AND DISCUSSION: We have found that the transmission of visual signals from retina to visual cortex is negatively influenced by the loss of Npc1 function. In fact, the VEP response of Npc1 (-/-) mice displayed a highly significant increase in the latency compared to that of Npc1 (+/+) mice. HPssCD administration fully rescued this defect and counteracted the cholesterol accumulation in retinal ganglion cells and dorsal lateral geniculate nucleus neurons, as well as the myelin loss in optic nerve fibers and axons projecting to the visual cortex observed in of Npc1 (-/-) mice. By contrast, HPssCD administration had no effect on the VEP response of Npc1 (+/+) mice, further strengthening the treatment efficacy. CONCLUSIONS: This study pinpoints the analysis of VEP response as a potentially accurate and non-invasive approach to assess neural activity and visual information processing in NPC1 patients, as well as for monitoring the progression of the disease and assessing the efficacy of potential therapies.

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Challa, Naveen Kumar. "An electrophysiological study of chromatic processing in the human visual system : using visual evoked potentials and electroretinograms to study cortical and retinal contributions to human trichromatic vision." Thesis, University of Bradford, 2011. http://hdl.handle.net/10454/5343.

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The work in this thesis is concerned with examining the retinal and cortical contributions to human trichromatic colour vision. Chromatic processing at the cortex level was examined using visual evoked potentials (VEPs). These responses were elicited by chromatic spot stimuli, which were manipulated in order to selectively activate the chromatic processing system. Chromatic processing at the retinal level was examined using the electroretinograms (ERGs) for which cone isolating stimuli were used to assess the nature of L and M cone inputs to cone-opponent mechanisms. The results from the VEP experiments suggest VEP morphology is dependent upon 1) chromatic and or luminance contrast content of the stimulus, 2) stimulus size, and 3) extent to which the chromatic stimulus activates either the L/M or S/(L+M) opponent mechanism. The experiments indicate that chromatic stimulation is indexed by large N1 component and small offset responses. Optimal stimulus size for chromatic isolation is 2-4 ° along L/M axes and 6° along S/(L+M) axis. From the ERG experiments, It has been shown that the low (12Hz) and high (30Hz) temporal frequency flickering stimuli can isolate the chromatic and luminance processing mechanisms in the retina. For low temporal frequency ERGs, the L:M ratio was close to unity and L/M phase difference was close to 180°. For high temporal frequency ERGs, the L:M ratio was more than unity and L/M phase difference was close to 90°. In addition to this, the variation in L:M ratio across the retinal eccentricity was also examined. These results suggest, for the chromatic processing, L:M ratio is close to unity independent of retinal eccentricity and individuals. For the luminance processing, L:M ratio is more than unity and depends upon the region of the retina being stimulated. These findings indicate the maintenance of cone selective input for the chromatic processing across the human retina.

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Lee, Jin. "How fast can we see? : the latency development in human infants to pattern, orientation, and direction-reversal visual evoked potentials." Thesis, University of Oxford, 2013. http://ora.ox.ac.uk/objects/uuid:09c7d3e8-7031-43e4-b03a-fe2dba219ceb.

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The goal of this thesis is to track latency changes in three visual evoked potentials (VEP) stimuli as an indication of overall brain development, in order to provide a normative baseline to differentiate visual and neurological development from pathological processes. VEP- neural electrical activity recorded from the scalp surface and synchronized with visual stimulus transitions- is one of the common techniques in understanding infant vision development. Past work has concentrated on responses to pattern reversal and to the latency of the initial positive peak. Here we compare the timing of responses to pattern, orientation, and direction-reversal VEPs, and transient peak latencies to those calculated from the gradient of steady-state phase against reversal rate. The three stimuli were tested in 81 adults at 1- 16 r/s and 137 infants (3.6- 79.0 weeks) at 2- 8 r/s. Initial responses to orientation and direction were as fast as for contrast- around 100 ms, consistent with other findings that V1 is orientation selective. Cortical processing for both OR and DR yielded longer latencies (200 ms) by the calculated method, perhaps reflecting more involvement of higher visual processing in comparison to PR. Orientation and direction latencies also had a delayed onset and longer developmental period to reach maturity. Infants reached adult transient PR latency values by 15 weeks, for OR by 50 weeks, and for DR by 10 weeks. For the calculated latency, infants reached both adult PR and DR latencies by 30 weeks while OR showed little change across age. We successfully confirmed that (1) phase-based calculation of latency is effective, easy to use, and taps into a different cortical pathway; (2) motion processing has an additional, faster, subcortical pathway; (3) a parallel processing of initial contrast and orientation; and (4) later visual processing is not only developmentally delayed for all three stimuli but also more vulnerable to perinatal brain damage. These latency differences provided a baseline for clinical evaluations where identification of delayed latencies should aid early diagnosis and guide therapies for adults and infants.

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Notbohm, Annika [Verfasser], Christoph Siegfried [Akademischer Betreuer] Herrmann, and Jonas [Akademischer Betreuer] Obleser. "The role of Steady- State Visual Evoked Potentials in the study of brain oscillations / Annika Notbohm ; Christoph Siegfried Herrmann, Jonas Obleser." Oldenburg : BIS der Universität Oldenburg, 2017. http://d-nb.info/1127208616/34.

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Notbohm, Annika [Verfasser], Christoph S. [Akademischer Betreuer] Herrmann, and Jonas [Akademischer Betreuer] Obleser. "The role of Steady- State Visual Evoked Potentials in the study of brain oscillations / Annika Notbohm ; Christoph Siegfried Herrmann, Jonas Obleser." Oldenburg : BIS der Universität Oldenburg, 2017. http://nbn-resolving.de/urn:nbn:de:gbv:715-oops-30990.

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43

Oliveira, André Gustavo Fernandes de. "Desenvolvimento das funções de acuidade visual e sensibilidade ao contraste visual medidas por potenciais visuais provocados de varredura em crianças nascidas a termo e prematuras." Universidade de São Paulo, 2007. http://www.teses.usp.br/teses/disponiveis/47/47135/tde-07012008-162937/.

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A prematuridade ao nascimento é um fator de risco para a visão, podendo causar retinopatia, uma condição em que há descolamento da retina. Retinopatia da prematuridade ocorre em uma parcela relativamente pequena dos recém nascidos prematuros e não sabemos se os demais, cujo desenvolvimento visual é aparentemente normal, seguem de fato o mesmo curso que o observado em bebes nascidos após uma gestação completa, ou se também sofrem algum prejuízo devido ao nascimento prematuro. Alternativamente, estes bebês poderiam ter um desenvolvimento visual acelerado pela sua exposição mais longa ao mundo visual. Para saber se a condição de prematuridade acelera, retarda, ou não altera o desenvolvimento da visão, o presente trabalho comparou o desenvolvimento das funções de acuidade visual e de sensibilidade ao contraste espacial de luminância em bebês nascidos prematuros e a termo. O estudo utilizou o método dos Potenciais Visuais Corticais Provocados de Varredura para examinar essas funções. Possíveis correlações entre os limiares visuais obtidos durante o primeiro ano de vida e idade gestacional, índices de Apgar, e valores de peso ao nascimento, foram examinadas. Os participantes foram 57 bebês de ambos os sexos encaminhados pelo Hospital Universitário da Universidade de São Paulo, dos quais 31 prematuros e 26 nascidos a termo. As avaliações foram realizadas principalmente em 3 fases do desenvolvimento visual: 4, 6 e 12 meses de vida. Os bebês prematuros tiveram suas idades corrigidas com relação à idade gestacional para a comparação com os grupos de termos. Um grupo de 14 sujeitos adultos também foi avaliado com os mesmos estímulos visuais. As avaliações das funções de acuidade visual e sensibilidade ao contraste foram realizadas através do método de potenciais visuais corticais provocados de varredura. Eletrodos posicionados no escalpo da região occipital dos pacientes captaram as respostas eletrofisiológicas provocadas por estímulos gerados em um monitor de alta resolução por um sistema computadorizado (sistema NuDiva). Estes estímulos consistiam de grades quadradas com valor de contraste fixo (80%) para avaliação da acuidade visual, e grades senoidais de 4 freqüências espaciais: 0,2 , 0,8 , 2,0 e 4,0 ciclos por grau para a avaliação da sensibilidade ao contraste. Prematuros e termos não apresentaram diferenças estatísticas significantes nas funções visuais avaliadas em nenhuma fase do desenvolvimento. O pico de sensibilidade ao contraste ocorreu entre .8 e 2.0 cpg de 4 meses de idade. No sexto mês o pico deslocou-se para 2.0 cpg, e entre os meses 9 e 12 passou para freqüências espaciais mais altas, por volta de 4.0 cpg coincidindo com o pico encontrado para os adultos. Nossos dados sugerem que nem a experiência visual, maior nos prematuros em relação aos termos, nem o tempo de gestação, maior nos termos em relação aos prematuros, afetam o desenvolvimento da visão espacial em humanos.
Prematurity at birth is a risk factor for vision, since it may lead to retinopathy - a condition in which there is retinal detachment. Retinopathy of prematurity occurs in a relatively small percentage of premature infants and it is not known if the remainder, whose visual development is apparently normal, follow the same course as in term babies after a complete gestational period, or if they also suffer some loss from having been born before complete development. Alternatively, these babies might have an accelerated visual development due to their longer exposure to the visual world, compared to term babies. To examine if prematurity accelerates, slows down, or does not affect visual development, the present study compared the development of visual acuity and contrast sensitivity in premature and term babies. The study used the methodology of the sweep visual evoked potentials to examine these functions. Possible correlations between visual thresholds obtained during the first year of life and gestational age, apgar index and birth weight, were examined. Participants were 57 infants of both genders, recruited by the University Hospital of São Paulo University, of which 31 were prematurely born and 26 were term infants. Evaluations were performed at three visual developmental epochs: 4, 6 e 12 months of age. The age of preterm infants was corrected by their gestational ages in order to allow comparison with the term infants. Another group with 14 adult subjects was tested with the same visual stimulus. Visual acuity and contrast sensitivity tests were performed with the sweep visual evoked potential method. Electrodes placed over the infant\'s scalp at the occipital role recorded electrophysiological responses evoked to visual stimuli generated by a high resolution monitor of a computerized system. The stimuli were square wave gratings with 80% of contrast to evaluate visual acuity, and sine wave gratings of 4 spatial frequencies: 0,2 , 0,8 , 2,0 e 4,0 cycles per degree to evaluate contrast sensitivity. Preterm and term infants did not show statistical differences in the evaluated visual functions in any developmental phase. The contrast sensitivity peak occurred between 0.8 and 2.0 cpd at 4 months of age. At the sixth month the peak moved to 2.0 cpd and it was displaced to a higher spatial frequency (4.0 cpd) at 12 months, where it coincides with the adult SCS peak. Our data suggest that neither visual experience, longer in the preterm, nor gestational age, longer in the term infants, seems to affect spatial vision functions in humans.

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França, Valtenice de Cássia Rodrigues de Matos. "Desenvolvimento da acuidade visual e sensibilidade ao contraste em recém-nascidos pequenos para a idade gestacional por potenciais visuais evocados de varredura." Universidade de São Paulo, 2012. http://www.teses.usp.br/teses/disponiveis/47/47132/tde-19032013-144632/.

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Objetivo: Avaliar o desenvolvimento da Acuidade Visual (AV) de resolução de grades e a Sensibilidade ao Contraste (SC) de recém-nascidos de termo pequenos para a idade gestacional (PIG). Método: Medimos a AV e a SC de 126 recém-nascidos de termo com o potencial visual evocado de varredura (PVEv; Norcia & Tyler 1985). 73 recém-nascidos (Média de Idade = 11,3 ± 4,3 semanas) nasceram com o peso adequado para a idade gestacional - AIG (percentil 10; Alexander et al., 1996) e 53 recém-nascidos (Média de Idade = 9,2± 3,8 semanas) nasceram pequenos para a idade gestacional - PIG (percentil <10). Mediu-se o PVEv com o sistema PowerDiva (Norcia & Tyler, 1985; Chen et al., 2005) o qual gerou os estímulos e analisou as respostas provocadas. O PVEv foi registrado com três canais unipolares colocados em O1, Oz, and O2 relacionados ao eletrodo de referência no vertex. Utilizaram-se os estímulos de grades senoidais verticais em reversão de fase em 6 Hz com a luminância média de 161 cd/m2. Para medir a AV, o contraste de 80% era mantido fixo e a freqüência espacial aumentava linearmente em intervalos de 1 segundo, durante 10 segundos. Para avaliar a SC, a freqüência espacial de 0,5 cpg era mantida fixa e o contraste aumentava logaritmicamente em intervalos de 1 segundo, durante 10 segundos. Os resultados de ambas as funções visuais foram baseados na média vetorial de pelo menos três tentativas do PVEv. Analisou-se, também, a média do ruído e quatro medidas supralimiares: amplitude máxima (Amáx), razão sinal-ruído em Amáx (SNRmáx), fase em Amáx (máx) e a inclinação da reta do PVEv. Considerou-se o canal que registrou a AV e a SC mais alta, satisfazendo o critério rigoroso de fase e amplitude para assegurar que as respostas corticais eram confiáveis e significativamente acima do ruído. Resultados: O teste Qui-quadrado mostrou que uma proporção significativa de recém-nascidos PIG menores de 9 semanas de idade apresentava valores de AV e SC abaixo da média do grupo AIG com o peso ao nascimento igual ou acima do percentil 50 (P50). Além disso, nas medidas de AV, uma proporção significativa de recémnascidos PIG de 5 a 24 semanas de idade apresentava valores de Amáx, ruído médio e SNRmáx significativamente menores que a média do grupo AIG (P50). A ANOVA fatorial confirmou que a AV, SC, ruído médio e todas as medidas supralimiares apresentaram um desenvolvimento significativo, isto é, as médias dos valores para os recém-nascidos abaixo de 10 semanas de idade apresentavam-se significativamente menores do que as médias dos valores entre 10 e 24 semanas de idade. Além disso, a taxa de desenvolvimento de máx era semelhante para os dois grupos, assim como para os dados de desenvolvimento de fase de Hamer e Norcia (1994). Conclusões: Os recém-nascidos de termo pequenos para a idade gestacional apresentaram alterações no desenvolvimento da acuidade visual de resolução de grades e sensibilidade ao contraste para frequência espacial baixa, principalmente nos 2 primeiros meses de vida quando as alterações nos limiares foram mais evidentes. Além disso, as alterações significativas encontradas para o ruído médio e amplitudes supralimiares durante os seis primeiros meses de vida, mostram que mesmo se os limiares de acuidade visual e contraste não fossem afetados, efeitos neuronais significantes ocorreriam nas vias visuais que conduzem a resposta gerada pelo PVEv (Mirabella et al., 2006)
Objectives: To evaluate the development of cortical grating acuity (VA) and contrast sensitivity (CS) in term infants born small for gestational age (SGA). Methods: Using the sweep visual evoked potential (sVEP; Norcia & Tyler 1985), we measured cortical VA and CS in 126 term infants. Seventy-three (average age = 11.3 ± 4.34 weeks) were born with birthweight within normal limits (> 10th percentile; Alexander et al., 1996). 53 infants were born SGA (average age = 9.2 ± 3.8 weeks). sVEPs were measured using the PowerDiva system (Norcia & Tyler, 1985; Chen et al., 2005) which generated the stimuli and analyzed the evoked responses. The sVEP was recorded using 3 unipolar channels placed at O1, Oz, and O2 with a reference electrode at the vertex. Stimuli were vertical sinewave luminance gratings phase-reversing at 6 Hz with a mean luminance of 161 cd/m2. To measure VA, spatial frequency (SF) was swept linearly from low to high during a 10-second trial, generating ten 1-sec time bins of sVEP data. Grating contrast was fixed at 80% during the SF sweep. To evaluate CS, SF was fixed at 0.5 c/deg, and contrast was increased logarithmically across 10 1-sec recording epochs. The resulting sVEP data from both protocols were based on a vector average of a minimum of 3 sVEP trials. In addition to thresholds, we analyzed average noise (Nav), and 4 suprathreshold measures - peak amplitude (Apeak), signal-to-noise ratio at Apeak (SNRpeak), phase at Apeak (peak) and slope of the rising phase of the sVEP (m). The data used were those obtained from the recording channel generating the highest VA or CS while satisfying strict phase and amplitude criteria to ensure that the responses were reliable and significantly above the noise. Results: A Chi-squared test showed that a significant proportion of the young ( 9 weeks) SGA infants had values of VA and CS that were below the mean of control infants (with birthweights above the international 50th percentile). In addition, mean Nav, Apeak and SNRpeak for the whole group of SGA infants were below the means of control infants across the whole age range tested. A factorial ANOVA confirmed that VA, CS, Nav and all the suprathreshold measures underwent significant development; that is, the mean values prior to 10 weeks were significantly different than the mean values between 10 and 24 weeks. In addition, the rate of development of peak was similar for the two groups as well as to prior phase-development data Hamer and Norcia (1994). Conclusions: Birth at term with weight small for gestational age appears to significantly affect development of both cortical grating acuity and contrast sensitivity for low-SF gratings. Effects on thresholds are most evident in the first 2 months. Moreover, the significant effects we found in Nav and suprathreshold amplitudes throughout the first 6 months of life show that, even if acuity and contrast thresholds are not affected, significant neuronal effects occur in the visual pathways leading to the sVEP signal (Mirabella et al., 2006)

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Costa, Thiago Leiros. "Repercussões visuais da exposição ocupacional a uma mistura de solventes orgânicos: visão cromática e acromática em frentistas brasileiros." Universidade de São Paulo, 2010. http://www.teses.usp.br/teses/disponiveis/47/47132/tde-09022011-113352/.

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Objetivo: Avaliar repercussões da exposição ocupacional a uma mistura de solventes orgânicos sobre o desempenho visual de um grupo de frentistas. Método: Foram aplicados testes de ordenamento e discriminação de matizes, campo visual e sensibilidade ao contraste espacial de luminância em 25 frentistas (20 homens, M=36,4 anos, DP=8,9) e 25 controles sem histórico de exposição crônica a solventes (10 homens, M=33,8 anos, DP=8,8). As concentrações metabólitos urinários de tolueno (M=0,3 g/g de creatinina; DP=0,16) e xileno (M=0,1 g/g de creatinina; DP=0,02) e o tempo de trabalho (M=9,6 anos; DP=6,2) foram utilizados como indicativos da exposição dos frentistas. Os participantes foram submetidos a exame oftalmológico, e quando necessário, corrigir a acuidade visual para 20/20. Todas as medidas foram realizadas monocularmente com um olho escolhido ao acaso, com exceção do Potencial Visual Evocado Multifocal (PVEmf) e da campimetria. Para avaliar a visão de cores, utilizamos o Lanthony D15-d e Cambridge Colour Test 2.0. Na campimetria estática automatizada foi utilizado o protocolo branco-branco 24-2 do aparelho Humphrey Field Analyzer II-750i. A atividade elétrica visual cortical foi avaliada com o sistema de PVEmf Veris Science 5.2.4, utilizando um estímulo de 60 setores. A sensibilidade ao contraste espacial de luminância foi avaliada no teste Metropsis, para grades senoidais em 7 frequências espaciais de 0,2 a 20,0 cpg. Resultados: Os escores do grupo de frentistas e do grupo controle foram comparados pelo teste Mann-Whitney U. No teste de discriminação de cores (CCT), houve diferença estatística significativa entre controles e frentistas para a área total da elipse (p<0,01), elipticidade (p<0,05) e limiares nos eixos protan, deutan e tritan (p<0,05). No D15d houve diferença significativa entre os 8 dois grupos (p<0,01). Os dados da campimetria apresentaram diferenças significativas entre os dois grupos para as excentricidades de 90, 150 e 210, além dos valores de MD e PSD (p<0,05). Dos três frentistas avaliados com o PVEmf, todos apresentaram uma diminuição significativa (p<0,05) da amplitude do sinal (em relação a dados normativos) em um mínimo de 30 setores do campo visual, resultado que não foi observado no grupo controle. Nos testes de visão de cores, foi encontrada uma correlação (Spearman) positiva e significativa entre o tempo de trabalho e os índices do Lanthony D15d (p=0,52; p<0,05) e os limiares no eixo deutan (p=0,59; p<0,05). Na campimetria, houve correlações negativas significativas com o tempo de trabalho para a área da Fóvea (p=-051; p<0,05), e para os anéis de 30 (p=-0,46; p<0,05), 90 (p=-0,46; p<0,05) e 150 (p=-0,46; p<0,05). Não foi encontrada correlação significativa entre a sensibilidade ao contraste e o tempo de trabalho. Conclusões: Os resultados mostram alterações amplas e difusas no processamento visual em decorrência da exposição crônica a solventes orgânicos
Purpose: To evaluate the outcome of chronic occupational exposure to a mixture of solvents on the visual system of a group of gas station workers. Methods: 25 gas station workers (20 male; M=36,4 years old, SD=8,9) and 25 controls (10 male; M=33,8 years old, DP=8,8) with no history of chronic exposure to solvents were tested for hue discrimination and arrangement, spatial contrast sensitivity, visual field and multifocal VEPs. Urinary concentrations of toluene (M=0,3g/g of creatinine; Sd=0,16) and xylene metabolites (M=0,1 g/g creatinine; SD=0), along with the time of work (M=9,6 years; SD=6,2) were used as indicators of the exposure. The participants were submitted to an ophthalmologic examination and corrected the visual acuity to 20/20 whenever needed. All measurements were monocular (eye randomly chosen) and only one eye was tested, except for Multifocal Visual Evoked Potential (mfVEP) and the automated perimetry. Color was evaluated with the Lanthony D15d and Cambridge Colour Test 2.0. Automatic static perimetry used the white-on-white 24-2 protocol of the Humphrey Field Analyzer II-750i. Visual field was also evaluated with the mfVEP system Veris Science 5.2.4. Contrast sensitivity was measured with Metropsis software, using sine wave gratings of 0,2; 0,5; 1,0; 2,0; 5,0; 10,0 and 20,0 cpd. Results: The results for the two groups were compared using the Mann-Whitney U test. In the color discrimination test, the groups were significantly different for the thresholds in the three confusion axis tested (p<0,05), area of the ellipse (p<0,01) and ellipticity (p<0,05). In the color arrangement test, the two groups were significantly different (p<0,01). The automated perimetry results were also significantly different between groups for the 90, 150 e 210 eccentricity rings (p<0,05) and the MD and PSD values (p<0,05). Only three of the workers were tested with the mfVEP so far. All three had at least 30 sectors in the visual field 10 with significant loss of amplitude in the response (p<0,05, when compared to normative data). This result was not observed in the control group. The Spearman correlation coefficient was used to look for significant correlations between time of work and visual performance. For color vision, we found significant positive correlation between time of work and indexes of the Lanthony D15d (p=0,52; p<0,05) and deutan axis thresholds (p=0,59; p<0,05) for the CCT test. The analysis of sensitivity in eccentricity rings of perimetry data showed significant negative correlation with the time of work for the Fovea (p=-051; p<0,05) and rings of 30 (p=-0,46; p<0,05), 90 (p=-0,46; p<0,05) e 150 (p=-0,46; p<0,05). The contrast sensitivity data was not significantly correlated with time of work. Conclusions: The results presented here suggest that chronic occupational exposure to organic solvents leads to changes in the visual system function even when the exposure is within occupational safety limits. The results also suggest that the visual changes are extensive and diffuse

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Silva, Andrei Damian da. "Desenvolvimento de um dispositivo SSVEP rápido e confiável utilizando eletrodos a seco e frequências acima de 25 Hz." Universidade Federal de Goiás, 2018. http://repositorio.bc.ufg.br/tede/handle/tede/8215.

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This paper presents a new approach for the processing and classification of visual evoked potentials of steady state (SSVEP). It introduces a ensemble tree model that combines canonical correlation analysis data with methods based on estimation of power spectral density. The stimuli were created using LEDs, from 7.04 Hz to 38.46 Hz. Data were collected using the Texas Instruments ADS1299EEG-Fe and three electrodes. The tests were performed for different distances and light intensities to evaluate the performance of the algorithm under different conditions. In all, 22 participants were recruited, and the average classification was 99.1 ± 2.27% with fixed decision time of 1 second.
Este trabalho apresenta uma nova abordagem para o processamento e classificação de potenciais evocados visuais de estado estacionário (SSVEP). Este trabalho introduz um modelo de em aprendizagem por agrupamento de árvores de decisão que combina dados de análise da correlação canônica com métodos baseados na estimativa da densidade espectral de potência. Os estímulos foram criados utilizando LEDs, com frequência de 7.04 Hz até 38.46 Hz. Os dados foram coletados utilizando a placa ADS1299EEG-Fe da Texas Instruments e três eletrodos. Os testes foram realizados para diferentes distâncias e intensidades luminosas com o objetivo de avaliar o desempenho do algoritmo em condições diversas. Ao todo, 22 participantes foram recrutados e a taxa de acertos média foi de 99.1±2.27% com tempo de decisão fixo em 1 segundo.

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Turi, Federica. "Interface cerveau-ordinateur adaptée à l'utilisateur." Thesis, Université Côte d'Azur, 2020. https://tel.archives-ouvertes.fr/tel-03149221.

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Les interfaces cerveau-ordinateur (Brain-Computer Interface ou BCI) permettent la communication entre l’utilisateur et la machine, grâce à la traduction de l’activité cérébrale en commandes qui servent à contrôler différents dispositifs. De nombreuses limitations empêchent la diffusion des systèmes BCI dans des applications réelles, telles que la phase de calibration qui résulte de la variabilité entre sessions et entre sujets. Cette phase est fondamentale car elle permet de régler les paramètres nécessaires pour le bon fonctionnement du système, mais elle est considérée beaucoup trop longue et fatigante pour le sujet.L'objectif de cette thèse est de surmonter ces limites par de nouvelles méthodes basées sur l’amélioration ou le remplacement de la phase de calibration traditionnelle, en proposant le développement d'une BCI centrée sur l'utilisateur.D’abord, nous proposons deux systèmes BCI adaptés au sujet. Le premier concerne un clavier virtuel basé sur des potentiels évoqués modulés par code-modulated Visual Evoked Potential (c-VEP) où la phase de calibration traditionnelle est remplacée par une phase dans laquelle les paramètres de stimulation sont réglés de manière adaptée au sujet. Le deuxième concerne le développement d'un système basé sur l’imagination mentale (MI-BCI) pour un sujet à déficience motrice sévère (tétraplégie), dans le cadre d'une compétition internationale BCI en direct.Ensuite, nous proposons une auto-calibration pour le c-VEP BCI qui utilise les propriétés fondamentales de la réponse VEP pour prédire les mots à l'aide d'un dictionnaire, éliminant la phase de calibration.Les méthodes proposées ont montré des résultats prometteurs et ouvrent de nouvelles perspectives pour la diffusion des systèmes BCI plus adaptables à l'utilisateur
Brain-Computer Interface (BCI) allows communication between a user and a machine, by converting the user's brain activity into commands that control external devices. Many limitations prevent the diffusion of BCI systems in real applications, such as the calibration phase that is a consequence of the issue of variability across sessions and among users. The calibration phase is fundamental because it allows to set the main parameters to extract the relevant information from the electroencephalograpy (EEG) signal of the subject, but it is considered time consuming and tedious for the user.The objective of this thesis is to overcome these limitations by novel methods based on the improvement or even replacement of the traditional calibration phase, proposing the development of a user-centered BCI system.Firstly, we present a design to develop an adaptive BCI system for two different applications. The former deals with a code-modulated Visual Evoked Potential (c-VEP) speller where an adaptive parameter setting phase is proposed to replace the standard calibration phase. The latter application concerns the development of a Mental Imagery (MI) BCI for a disabled user, characterized by a long user-centered multi-stage training phase, in the context of a international BCI competition.Secondly, we propose an auto-calibration c-VEP BCI system exploiting the language information. In our model the fundamental properties that characterize the VEP response are used to predict the full word using a dictionary, eliminating the traditional calibration phase.The proposed methods showed promising results and open new perspectives to the diffusion of BCI

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Haro, Filomena Maria Buosi de. "Desenvolvimento da acuidade visual de resolução de grades em prematuros durante o primeiro ano de vida : estudo eletrofisiológico pelo registro dos potenciais visuais evocados de varredura." Universidade de São Paulo, 2003. http://www.teses.usp.br/teses/disponiveis/5/5141/tde-08092014-142658/.

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Objetivos: determinar a acuidade visual de resolução de grades (AV) durante o primeiro ano de vida por meio dos registros dos potenciais visuais evocados de varredura em grupos de crianças nascidas prematuramente (RNPT) e a termo (RNT); comparar os valores finais da AV no grupo RNPT em relação à idade gestacional e ao desenvolvimento neuropsicomotor e comparar as curvas de desenvolvimento visual entre os grupos RNPT e RNT. Casuística e métodos: Estudo realizado em 25 RNT e 36 RNPT acompanhados em ambulatório e submetidos a avaliações oftalmológica e neuropediátrica. O grupo RNPT foi dividido em subgrupos com relação a idade gestacional e desenvolvimento neuropsicomotor. Para a medida da AV foi utilizado o aplicativo NuDIVA (\"Digital Infant Visual Assessment\") calculando-se a AV em logaritmo do mínimo ângulo de resolução (logMAR) através de curva de regressão linear, relacionando-se a amplitude do potencial do segundo harmônico à freqüência espacial linear. Na análise estatística utilizou-se método de Fischer, teste t, análise de variância (ANOVA) e teste para comparação entre retas de regressão linear simples. O nível de significância foi fixado em 0,05. Resultados: Estrabismo foi detectado em cinco crianças, todas do grupo RNPT, quatro delas com alteração neurológica (p=0,07). Erros de refração com necessidade de prescrição óptica foi encontrado em seis crianças, todas do grupo RNPT (p=0,07). A medida da AV foi obtida com sucesso em 96,4% dos casos, sendo ao final do primeiro ano de vida significativamente inferior nos RNPT com alteração neurológica (p<0,05). A medida da AV estimada ao nascimento foi maior em todos os RNPT com relação aos RNT (p<0,05) porém a velocidade de aquisição da AV foi maior no grupo RNT (p<0,05). Conclusões: A AV pôde ser facilmente determinada durante o primeiro ano de vida tanto em RNPT quanto em RNT sendo seus valores semelhantes, com exceção dos RNPT que apresentaram alteração neurológica. Todos os RNPT apresentaram desenvolvimento visual semelhante, porém, significativamente inferior ao encontrado para os RNT
Purpose: Determine the grating visual acuity (VA) of a group of preterm infants using sweep visual evoked potentials (sweep-VEP). Compare the development of VA of these infants to that of normal full-term infants, with respect to: gestational age, neuropsychomotor development and visual development. Methods: The study was conducted on 25 preterm and 36 full-term infants, with follow-up ophthalmologic and neuropediatric evaluations. The preterm infants were divided into subgroups in accordance with their gestational age and neurological development. VA was assessed using the Digital Infant Visual Assessment (NuDiva) sweep-VEP system, expressed in logMAR, and threshold grating acuities were estimated using the VEP second harmonic amplitudes, determined by a linear regression line drawn through the highest spatial frequency peak and the spatial frequency at which signal amplitude reaches the noise level. Statistical analysis was performed using the Fisher, Student-t test, analysis of variance (ANOVA) and comparison by simple linear regression test between the two groups. The significance level was 0.05. Results: Strabismus was detected in five preterm infants; four of these had neurological alterations (p=0.07). Prescription for refractive errors was necessary in six preterm infants (p=0.07). Grating VA was assessable in 96.4% of the infants; preterm infants with neurological alterations had significantly lower grating VA (p<0.05) at the end of the first year. Early VA scores were higher in all of the preterm infants compared to the full term infants (p<0,05) but at the end of the first year of life the VA was improving at a higher rate in the full term group (p<0.05)

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Torres, Soriano Desireé. "Electrodiagnóstico: protocolo clínico y estandarización de Electrorretinografía (ERG)y Potenciales Evocados Visuales (PEV)en el perro beagle." Doctoral thesis, Universidad de Murcia, 2010. http://hdl.handle.net/10803/10991.

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La presente tesis se ha basado en conseguir dos objetivos fundamentales: diseñar un protocolo clínico de electrodiagnóstico para obtener el electrorretinograma (ERG) y los potenciales evocados visuales (PEV) en el perro beagle, y elaborar un estándar de los resultados para esta raza.Hemos establecido un protocolo clínico de electrodiagnóstico adaptado a nuestro equipo de diagnóstico, a las características de nuestros pacientes y, en general, a los recursos materiales que teníamos a nuestra disposición. De este modo, hemos conseguido realizar un protocolo de corta duración que nos permite evaluar la funcionalidad de las vías visuales del perro y detectar posibles anomalías.Concluimos que el protocolo que hemos establecido nos permite registrar adecuadamente el ERG y los PEV para el perro beagle, así como obtener resultados fiables y reproducibles que podemos considerar como estándar para esta raza canina y este equipo de electrodiagnóstico.
The aims of this thesis were firstly to design a clinical protocol for Electro, electroretinography (ERG) and visual evoked potential (VEP) in the Beagle dog and, secondly, to develop a performance standard for this breed. A clinical electrodiagnostic protocol adapted to our diagnostic equipment was established. This protocol considered the characteristics of the patients as well as the material resources at our Institution. This protocol allowed us to evaluate the functionality of the visual pathways in order to detect any anomalies. It can be concluded that the protocol established in this Thesis allows to record accurately the ERG and the VEP of Beagle dogs. Moreover, the results are reliable and reproducible and it could be considered as a good standard for this breed when these electrodiagnosis tools are employed.

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Istrefaj, Mirushe Mjekiqi. "MÄTNING AV SYNNERVENS FUNKTION." Thesis, Malmö universitet, Fakulteten för hälsa och samhälle (HS), 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:mau:diva-26613.

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Visual Evoked Potentials (VEP) är en elektrofysiologisk undersökningsmetod som används inom klinisk neurofysiologi. Undersökningen görs för att analysera synnervsfunktionen. Metoden går ut på att mäta den tid det tar för synbarken att registrera visuella synintrycken som näthinnan utsätts för. För att en optimal tolkning av det människan ser ska kunna ske måste elektriska signaler kunna fortledas från näthinnan till synbarken via en fullt fungerande, frisk synnerv. Skador på synnerven beror oftast på optikusneurit och misstänks oftast vara ett tidigt tecken multipel skleros. Undersökningen är därför ett viktigt komplement för diagnostiska ändamål. Syftet med studien var att jämföra normalvärden från befintlig apparatur med ny apparatur som kan komma att användas till VEP-undersökningar. Även en jämförelse av normalvärden med standardrutor och större rutor gjordes för att eventuellt kunna använda större rutor på patienter med försämrad visus. Undersökning hur normalvärden skiljer sig beroende på kön och ålder gjordes också. Totalt deltog 28 deltagare varav 27 deltagares rådata samlades in och analyserades genom stapeldiagram, t-test och korrelationsdiagram. Deltagarna var mellan 20-70år och delades upp i 18 kvinnor och 9 män. Utifrån studiens resultat kan ett påstående om att ny apparatur kan komma till att kunna användas med samma normalvärde för befintlig apparatur. Även större rutor visades kunna vara användbara vid behov. Dock behöver studien fortsätta med en större testgrupp för att erhålla tillförlitliga resultat rent kliniskt.
Visual evoked potentials (VEP) is an electrophysiological method which is done by the clinical neurophysiology clinics. The examination is done when the purpose is to analyze the visual pathways. The method is done by measuring the latency from the retina to the occipital lobe. In order for the brain to understand an image the optic nerve needs to be intact and fully functional. Nerve damage in the optic nerve occurs often from optikusneuritis. Optikusneuritis is often assumed as an early sign of multiple sclerosis. This study is therefore an important complement for diagnostic purposes. The purpose of this study was to compare normal values from the existing equipment with the new equipment so the new equipment can be used for VEP-examinations. A comparison of normal values for standard squares and lager squares was also made, to potentially use larger squares in patients with deteriorated visual acuity. The study investigated also how normal values differ according to gender and age. A total of 28 participant participated in the study, of which 27 participants values were analyzed. The results were analyzed by bar graphs, t-test and correlation charts. The participants were 18 women and 9 men between 20-70 years. Based on the results of the study, a claim that the new equipment may be used with the same normal values as the existing equipment. Even larger squares were shown to maybe be useful when needed in some patients. However, the study needs to continue with a larger test group to obtain reliable results. This so the clinic can use the new equipment in VEP’s.

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