Dissertations / Theses on the topic 'Visual evoked response'
To see the other types of publications on this topic, follow the link: Visual evoked response.
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 36 dissertations / theses for your research on the topic 'Visual evoked response.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
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.
Full textAbstract:
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
2
Rudduck, Gillian A. "The chromatic visual evoked response as an indication of visual development." Thesis, Aston University, 1993. http://publications.aston.ac.uk/14607/.
Full textAbstract:
In an endeavour to provide further insight into the maturation of the cortical visual system in human infants, chromatic transient pattern reversal visual evoked potentials to red/green stimuli, were studied in a group of normal full term infants between the ages of 1 and 14 weeks post term in both cross sectional and longitudinal studies. In order to produce stimuli in which luminance cues had been eliminated with an aim to eliciting a chromatic response, preliminary studies of isoluminance determination in adults and infants were undertaken using behavioural and electrophysiological techniques. The results showed close similarity between the isoluminant ratio for adults and infants and all values were close to photometric isoluminance. Pattern reversal VEPs were recorded to stimuli of a range of red/green luminance ratios and an achromatic checkerboard. No transient VEP could be elicited with an isoluminant chromatic pattern reversal stimulus from any infant less than 7 weeks post term and similarly, all infants more than 7 weeks post term showed clear chromatic VEPs. The chromatic response first appeared at that age as a major positive component (P1) of long latency. This was delayed and reduced in comparison to the achromatic response. As the infant grew older, the latency of the P1 component decreased with the appearance of N1 and N by the 10th week post term. This finding was consistent throughout all infants assessed. In a behavioural study, no infant less than 7 weeks post term demonstrated clear discrimination of the chromatic stimulus, while those infants older than 7 weeks could do so. These findings are reviewed with respect to current neural models of visual development.
3
Hobley, Angela J. "The investigation of the primary response of the flash visual evoked response." Thesis, Aston University, 1988. http://publications.aston.ac.uk/14616/.
Full textAbstract:
The topographical distribution of the early components of the flash visual evoked response (VER) were investigated using a twenty channel brain mapping system. Thirty subjects, ranging in age from 21 to 84 years, had flash VERs recorded using the standard 10-20 electrode system to a balanced non-cephalic reference. The subjects were divided into three age groups: a young group, a middle group and an older group. The P2 component (positive component around 100-120 msec) of the flash VER was recorded consistently over the occipital region throughout the age range, as was a frontal negative component (N120) of about the same latency. Only the young age group had this single negative component on the frontage channels, whilst the middle age group showed an additional negative component at around 75 msec (N75). Neither group had a recordable P1 component (positive component around 60-75 msec) over the occipital region. The older age group showed both P1 and P2 components over the occipital region with the distribution of the P1 component being more widespread anteriorly. The frontal channels showed both the negative N75 and the later N120 components. The frontal negative components were shown not to be related to the electroretinogram or the balanced non-cephalic reference, but were affected by the type of stimulation. Responses recorded to both pattern reversal and onset/offset stimulation did not show the frontal negative potentials seen with flash stimulation. It was shown that the P1 component is more readily recordable in the elderly and is preceded during middle age by the development of a frontal negative component at around the same latency. The changing morphology of the negative activity in the frontal region across the age range suggests that the use of an Fz reference would produce an artificial P1 component in the middle age group and an enhancement of this component in the elderly, as well as enhance the P2 component in all ages.
4
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.
Full textAbstract:
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.
5
Lloyd, Robyn School of Optometry & 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.
Full textAbstract:
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.
6
De, Faria Newton. "A non-invasive visual evoked cortical potential test for detection of early glaucoma damage /." Digital version accessible at:, 1998. http://wwwlib.umi.com/cr/utexas/main.
Full text
7
Stevens, Jean-Luc Richard. "Spatiotemporal properties of evoked neural response in the primary visual cortex." Thesis, University of Edinburgh, 2018. http://hdl.handle.net/1842/31330.
Full textAbstract:
Understanding how neurons in the primary visual cortex (V1) of primates respond to visual patterns has been a major focus of research in neuroscience for many decades. Numerous different experimental techniques have been used to provide data about how the spatiotemporal patterns of light projected from the visual environment onto the retina relate to the spatiotemporal patterns of neural activity evoked in the visual cortex, across disparate spatial and temporal scales. However, despite the variety of data sources available (or perhaps because of it), there is still no unified explanation for how the circuitry in the eye, the subcortical visual pathways, and the visual cortex responds to these patterns. This thesis outlines a research project to build computational models of V1 that incorporate observations and constraints from an unprecedented range of experimental data sources, reconciling each data source with the others into a consistent proposal for the underlying circuitry and computational mechanisms. The final mechanistic model is the first one shown to be compatible with measurements of: (1) temporal firing-rate patterns in single neurons over tens of milliseconds obtained using single-unit electrophysiology, (2) spatiotemporal patterns in membrane voltages in cortical tissues spanning several square millimeters over similar time scales, obtained using voltage-sensitive-dye imaging, and (3) spatial patterns in neural activity over several square millimeters of cortex, measured over the course of weeks of early development using optical imaging of intrinsic signals. Reconciling this data was not trivial, in part because single-unit studies suggested short, transient neural responses, while population measurements suggested gradual, sustained responses. The fundamental principles of the resulting models are (a) that the spatial and temporal patterns of neural responses are determined not only by the particular properties of a visual stimulus and the internal response properties of individual neurons, but by the collective dynamics of an entire network of interconnected neurons, (b) that these dynamics account both for the fast time course of neural responses to individual stimuli, and the gradual emergence of structure in this network via activity-dependent Hebbian modifications of synaptic connections over days, and (c) the differences between single-unit and population measurements are primarily due to extensive and wide-ranging forms of diversity in neural responses, which become crucial when trying to estimate population responses out of a series of individual measurements. The final model is the first to include all the types of diversity necessary to show how realistic single-unit responses can add up to the very different population-level evoked responses measured using voltage-sensitive-dye imaging over large cortical areas. Additional contributions from this thesis include (1) a comprehensive solution for doing exploratory yet reproducible computational research, implemented as a set of open-source tools, (2) a general-purpose metric for evaluating the biological realism of model orientation maps, and (3) a demonstration that the previous developmental model that formed the basis of the models in this thesis is the only developmental model so far that produces realistic orientation maps. These analytical results, computational models, and research tools together provide a systematic approach for understanding neural responses to visual stimuli across time scales from milliseconds to weeks and spatial scales from microns to centimeters.
8
Jones, Keith Shawn. "AN EVALUATION OF A STEADY-STATE VISUAL EVOKED RESPONSE-BASED CONTROL." University of Cincinnati / OhioLINK, 2000. http://rave.ohiolink.edu/etdc/view?acc_num=ucin971880840.
Full text
9
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.
Full text
10
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.
Full text
11
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.
Full text
12
Nesfield, Catheryn J. "The effect of stimulus location on the major components of the visual evoked response." Thesis, Aston University, 1992. http://publications.aston.ac.uk/14629/.
Full textAbstract:
The topographical distribution of the pattern reversal Visual Evoked Response (VER) was recorded from a localised montage of 20 electrodes over the visual cortex. The response was recorded after stimulation with a black and white checkerboard stimulus. The effect of field location on the major components was investigated in 11 subjects (age range (23-55). The major components of the half field response were; a negative around 75ms (N75) followed by a positivity around 80ms (P80), then a positivity around 100ms (P100) followed by another positivity at around 120ms (P120) and a negativity at approximately 145ms (N145). No effect of field size could be demonstrated on either the amplitude or latency of the late negativity, N145. No significant effect of field size or location was shown on the latency of the P100 response. A delay previously shown in the upper half field response was therefore not substantiated. In contrast the amplitude of the major positivity, P100 was significantly affected by the field size and location. The amplitude of both P100 and N145 were significantly reduced following upper field stimulation when compared with the lower field response. No significant amplitude difference between the upper and lower field responses was demonstrated using electroretinography, the amplitude may therefore be reduced as a result of the ventral position of the upper field representation on the visual cortex. The lateral half field VEP was compared with the distribution of the visual evoked magnetic response (VEMR). The distribution of the VEMR supported the proposal that the paradoxical lateralisation of the VEP half field response is the result of the source being directed ipsilaterally. The morphology of the VEP following octant and double octant stimulation suggests that the response is generated in the striate cortex, with a reversal in response distribution following stimulation of the upper vertical and horizontal meridia.
13
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.
Full text
14
Evans, Jennifer Anne. "Changing the shape of circadian rhythms with light no brighter than moonlight." Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 2007. http://wwwlib.umi.com/cr/ucsd/fullcit?p3258782.
Full textAbstract:
Thesis (Ph. D.)--University of California, San Diego, 2007.Title from first page of PDF file (viewed June 8, 2007). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references (p. 169-188).
15
Baud-Bovy, Gabriel. "A gaze-addressing communication system using artificial neural networks." PDXScholar, 1992. https://pdxscholar.library.pdx.edu/open_access_etds/4258.
Full textAbstract:
Severe motor disabilities can render a person almost completely incapable of communication. Nevertheless, in many cases, the sensory systems are intact and the eye movements are still under good control. In these cases, one can use a device such as the Brain Response Interface (BRI) to command a remote control (e.g. room temperature, bed position), a word-processor, a speech synthesizer, and so on.
16
Nuttall, Rachel Corinne [Verfasser], Christian [Akademischer Betreuer] Sorg, Afra [Gutachter] Wohlschläger, and Markus [Gutachter] Ploner. "Evoked response variability across alpha oscillatory sources to visual flicker stimulation: An investigation in humans using electrophysiological and blood-oxygenation recordings / Rachel Corinne Nuttall ; Gutachter: Afra Wohlschläger, Markus Ploner ; Betreuer: Christian Sorg." München : Universitätsbibliothek der TU München, 2021. http://d-nb.info/1228073260/34.
Full text
17
Clay, Gary Robert. "Integrated scenic modeling of environmentally induced color changes in a coniferous forest canopy." Diss., The University of Arizona, 1995. http://hdl.handle.net/10150/187420.
Full textAbstract:
The relationship between the changes in color values of scenic landscapes, and the corresponding shifts in viewers' preferences to those changed environments, was the focus of the presented research. Color modifications, either natural or based on some human intervention, provide visual clues that an environment has undergone some transformation. These color changes can occur at both the micro and macro scale, can having temporal dimensions, and can be a result of combinations of both physical landscape change, and shifts in an observer's perspective with respect to that landscape. The research reviewed two existing models and related them in an integrated program of scenic change analysis. The first, a bio-physical remote sensing model, identified the relationships between the existing bio-physical environmental conditions and measured color signatures of selected landscape features. The second, a psychophysical perception model, established relationships between the landscape's bio-physical attributes and measured perceptual responses to those environments. By merging aspects of each model, the research related the changing scenic color patterns with observers' responses to those changed environments. The research methodology presented a program of scenic change analysis incorporating several technologies including (1) ground-based biological inventories, (2) remote sensing, (3) geographic information systems (GIS), and (4) computer visualization. A series of investigations focused on landscape scenes selected from a high elevation coniferous forest in southern Utah. Three initial scenic investigations compared (1) the impact of changing view angles on scenic color values, (2) color shifts due to changing sun-illumination angles within a day, and (3) color shifts due to changing biological conditions over a 12-month period. A fourth investigation measured the color changes caused by a spruce bark beetle outbreak, and developed a series of color signatures to simulate the color shifts indicative of an outbreak at different stages of development. These signatures were applied to digitized site photographs to produce a series of visualizations displaying different levels of beetle damage. The visualizations were then applied in a series of perceptual experiments to test the precision and reliability of the visual simulations.
18
Fassnidge, Christopher. "The visually-evoked auditory response." Thesis, City, University of London, 2018. http://openaccess.city.ac.uk/19689/.
Full textAbstract:
In synaesthesia a sensation in one modality triggers a consciously perceived sensation in another sensory modality or cognitive domain. In this thesis we investigate auditory sensation that are induced by dynamic visual stimuli, akin to hearing-motion synaesthesia (Saenz and Koch, 2008). We term this the Visually-Evoked Auditory Response (vEAR). We first establish the prevalence of vEAR in a random sample, with questionnaire responses indicating a higher prevalence (as many as 1 in 5) than canonical synaesthesias. We report that those who experience vEAR showed better performance compared to controls when discriminating between ‘Morse-code’ style rhythmic sequences in the visual domain, as did Saenz and Koch (2008). We also demonstrate that vEAR is perceptually real enough to interfere with hearing real world sounds. We then demonstrate that in control subjects Transcranial Alternating Current Stimulation (TACS), when applied over the temporal versus the occipital lobes, impairs auditory versus visual sequence discrimination respectively. However, temporal TACS improved visual and occipital TACS improved auditory sequence discrimination performance. This suggests the presence of normally-occurring mutual alpha-mediated competitive inhibition of the two cortices. This TACS effect was not seen in individuals with vEAR, indicating that their auditory and visual cortices are able to cooperate to perform the task despite disruption from TACS. Finally, we investigate the types of visual stimuli that best evoke vEAR, and the types of people who tend to experience it. We conducted a large online survey in which respondents rated the amount of vEAR evoked by a series of silent videos depicting types of motion. The predictiveness of a real-world sound was identified as a major contributor to ratings in all respondents, while motion energy (raw changes in light over space and time) specifically influenced ratings in those who experience vEAR. We also report demographic and trait questions relating to auditory perception that predict higher ratings, including the frequency one experiences music imagery in their head, or whether they have tinnitus or types of synaesthesia. We conclude that vEAR results from both high and low-level connectivity between the visual and auditory cortices and an atypical inhibition of these connections.
19
Wen, Yaqin. "Spatial and temporal characteristics of multifocal visual evoked responses." Thesis, University of Nottingham, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.432031.
Full text
20
Dixon, Thomas Oliver. "An electrophysiological examination of visuomotor activity elicited by visual object affordances." Thesis, University of Plymouth, 2016. http://hdl.handle.net/10026.1/6758.
Full textAbstract:
A wide literature of predominantly behavioural experiments that use Stimulus Response Compatibility (SRC) have suggested that visual action information such as object affordance yields rapid and concurrent activation of visual and motor brain areas, but has rarely provided direct evidence for this proposition. This thesis examines some of the key claims from the affordance literature by applying electrophysiological measures to well established SRC procedures to determine the verities of the behavioural claims of rapid and automatic visuomotor activation evoked by viewing affording objects. The temporal sensitivity offered by the Lateralised Readiness Potential and by visual evoked potentials P1 and N1 made ideal candidates to assess the behavioural claims of rapid visuomotor activation by seen objects by examining the timecourse of neural activation elicited by viewing affording objects under various conditions. The experimental work in this thesis broadly confirms the claims of the behavioural literature however it also found a series of novel results that are not predicted by the behavioural literature due to limitations in reaction time measures. For example, while different classes of affordance have been shown to exert the same behavioural facilitation, electrophysiological measures reveal very different patterns of cortical activation for grip-type and lateralised affordances. These novel findings question the applicability of the label ‘visuomotor’ to grip-type affordance processing and suggest considerable revision to models of affordance. This thesis also offers a series of novel and surprising insights into the ability to dissociate afforded motor activity from behavioural output, into the relationship between affordance and early visual evoked potentials, and into affordance in the absence of the intention to act. Overall, this thesis provides detailed suggestions for considerable changes to current models of the neural activity underpinning object affordance.
21
Huang, Bao-Quey. "Visually evoked startle response in the cod (Gadhus Morhua)." Thesis, University of Aberdeen, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.331943.
Full text
22
Slaven, Antoinette. "Visual evoked magnetic responses (VEMR) to flash and pattern reversal stimulation." Thesis, Aston University, 1992. http://publications.aston.ac.uk/14634/.
Full textAbstract:
The problems of using a single channel magnetometer (BTi, Model 601) in an unshielded clinical environment to measure visual evoked magnetic responses (VEMR) were studied. VEMR to flash and pattern reversal stimuli were measured in 100 normal subjects. Two components, the P100M to pattern reversal and P2M to flash, were measured successfully in the majority of patients. The mean latencies of these components in different decades of life were more variable than the visual evoked potentials (VEP) that have been recorded these stimuli. The latency of the P100M appeared to increase significantly after about 55 years of age whereas little change occurred for the flash P2. Variations in blur, check size, stimulus size and luminance intensity on the latency and amplitude of the VEMR were studied. Blurring a small (32') check significantly increased latency whereas blurring a large (70') check had little effect on latency. Increasing check size significantly reduced latency of the P100M but had little effect on amplitude. Increasing the field size decreases the latency and increases the amplitude of the P100M. Within a normal subject, most of the temporal variability of the P100M appeared to be associated with run to run variation rather than between recording sessions on the same day or between days. Reproducibility of the P100M was improved to a degree by employing a magnetically shielded room. Increasing flash intensity decreases the latency and increases the amplitude of the P2M component. The magnitude of the effects of varying stimulus parameters on the VEMR were frequently greater than is normally seen in the VEP. The topography of the P100M and P2M varied over the scalp in normal subjects. In addition, full field responses to a large check could be explained approximately as the sum of the half field responses and were consistent with the cruciform model of the visual cortex. Preliminary source localisation data suggested a shallower source in the visual cortex for the flash P2M compared with the P100M. The data suggest that suitable protocols could be devised to obtain normative data of sufficient quality to use the VEMR to flash and pattern clinically.
23
Degg, Christopher. "The visually evoked magnetic response (VEMR) to a pattern onset/offset stimulus." Thesis, Aston University, 1993. http://publications.aston.ac.uk/14608/.
Full textAbstract:
This study characterizes the visually evoked magnetic response (VEMR) to pattern onset/offset stimuli, using a single channel BTi magnetometer. The influence of stimulus parameters and recording protocols on the VEMR is studied with inferences drawn about the nature of cortical processing, its origins and optimal recording strategies. Fundamental characteristics are examined, such as the behaviour of successive averaged and unaveraged responses; the effects of environmental shielding; averaging; inter- and intrasubject variability and equipment specificity. The effects of varying check size, field size, contrast and refractive error on latency, amplitude and topographic distribution are also presented. Latency and amplitude trends are consistent with previous VEP findings and known anatomical properties of the visual system. Topographic results are consistent with the activity of sources organised according to the cruciform model of striate cortex. A striate origin for the VEMR is also suggested by the results to quarter, octant and annulus field stimuli. Similarities in the behaviour and origins of the sources contributing to the CIIm and CIIIm onset peaks are presented for a number of stimulus conditions. This would be consistent with differing processing event in the same, or similar neuronal populations. Focal field stimuli produce less predictable responses than full or half fields, attributable to a reduced signal to noise ratio and an increased sensitivity to variations in cortical morphology. Problems with waveform peak identification are encountered for full field stimuli that can only be resolved by the careful choice of stimulus parameters, comparisons with half field responses or with reference to the topographic distribution of each waveform peak.
24
Suttle, Catherine M. "Development of visual evoked responses to tritan,red-green and luminance stimuli in human infants." Thesis, Aston University, 1997. http://publications.aston.ac.uk/14649/.
Full textAbstract:
The principal aim of this work was to investigate the development of the S-cone colour-opponent pathway in human infants aged 4 weeks to 6 months. This was achieved by recording transient visual evoked responses to pattern-onset stimuli along a tritanopic confusion axis (tritan stimuli) at and around the adult isoluminant match. For comparison, visual evoked responses to red-green and luminance-modulated stimuli were recorded from the same infants at the same ages. The transient VEP allowed observation of response morphology as luminance differences were introduced to the chromatic stimuli. In this way, an estimate of isoluminance was possible in infants. Estimated isoluminant points for a group of six infants aged 6 to 10 weeks closely approximated the adult isoluminant match. Abnormalities of the visual evoked responses to tritan, red-green and luminance-modulated stimuli in an infant with cystic fibrosis are reported. The results suggest abnormal function of the retino-striate visual pathway in this infant, and it is argued that these may be secondary to his illness. A group of nine healthy infants demonstrated evoked responses to tritan stimuli by 4 to 10 weeks and to red-green stimuli by 6 to 11 weeks post-term age. Responses to luminance-modulated stimuli were present in all nine infants at the earliest age tested, namely 4 weeks post-term. The slightly earlier age of onset of evoked responses to tritan stimuli than for red-green may be explained by the relatively lower cone contrast afforded by red-green stimuli. Latency of the evoked response to both types of chromatic stimuli and to luminance-modulated stimuli decreased with age at a similar rate.
25
Hashimoto, Tadashi. "Temporal profile of visual evoked responses to pattern reversal stimulation analyzed with whole-head magnetometer." Kyoto University, 1999. http://hdl.handle.net/2433/181243.
Full text
26
Robertson, Anthony William Carleton University Dissertation Psychology. "Spatial pattern visually-evoked responses recorded from the mid-temporal scalp region of humans." Ottawa, 1985.
Find full text
27
Guhr, Susanne. "Visuell evozierte Flussgeschwindigkeitänderungen in der A. cerebri posterior bei Normalprobanden und Patienten mit Leitungsverzögerungen im Sehbahnbereich." Doctoral thesis, Humboldt-Universität zu Berlin, Medizinische Fakultät - Universitätsklinikum Charité, 2002. http://dx.doi.org/10.18452/14779.
Full textAbstract:
In der vorliegenden Arbeit werden am Beispiel visuell evozierter Flussgeschwindigkeitsänderungen die Anpassung der zerebralen Hämodynamik an Änderungen der Gehirnaktivität untersucht. Dazu wurde das nichtinvasive Verfahren der transkraniellen Dopplersonographie angewendet. Ziele der Arbeit waren das Erstellen von Normwerten der Latenzen und Amplituden visuell evozierter Geschwindigkeitsänderungen an einer Gruppe von Normalprobanden sowie die Prüfung der Sensitivität der zeitlichen Auflösung dieses Verfahrens. Die Untersuchungen wurden an einer Gruppe von 20 Normalprobanden und an einer Gruppe von 16 Patienten, welche eine Leitungsverzögerung im vorderen Sehbahnbereich (nachgewiesen mit den Visuell Evozierten Potentialen anhand der P100) zeigten, vorgenommen. Die Lichtstimulation erfolgte mit einer LED-Blitzbrille und einer Stimulationszeit von jeweils 10 s "on" und "off" mit einer Frequenz von 15 Hz bei konstanter Lichtintensität. In der Kontrollgruppe ermittelten wir einen reaktiven Geschwindigkeitsanstieg von 16 %. Der Anstieg der Flussgeschwindigkeit erfolgte nach 1,4 s bzw. nach 1 s bei Flussantworten, die gleich mit einem Anstieg der Geschwindigkeit begannen. Das initiale Maximum wurde nach 5,6 s erreicht, 2,9 s nach Stimulationsende begann die Geschwindigkeit wieder abzufallen. Außer bei den Latenzwerten bis zum Anstieg ohne vorherigen Abfall der Flussgeschwindigkeit gab es keine signifikanten Unterschiede zwischen den beiden untersuchten Gruppen. Die von uns ermittelten Werte lagen in den Größenordnungen der Ergebnisse anderer Studien mit ähnlichem Versuchsaufbau. Auch die unterschiedlichen Verläufe der Flussantworten wurden bis auf das "initiale undershoot" auch von anderen Autoren beschrieben. Als Erklärung dafür diskutierten wir Aktivierungen anderer Hirnareale und eine Umverteilung des Blutflusses dorthin zu Beginn. Die zeitliche Auflösung der Dopplersonographie ist gut geeignet zeitliche Abläufe der zerebralen Hämodynamik zu untersuchen. Sie ist aber nicht sensitiv genug Leitungsverzögerungen im vorderen Sehbahnbereich zu erfassen. Die Möglichkeiten der Anwendung in der klinischen Routine liegen daher in der Untersuchung von Störungen der neurovaskulären Kopplung.In this paper we present an investigation about the adaption of the cerebral hemodynamic to changing of the brain activation at the example of visual evoked blood flow response. Therefore we used the transcranial Doppler sonography as a noninvasive method. The aim of the work was to determine normal values of the latencies and amplitudes of visual evoked flow changing and to investigate the sensitivity of the temporal resolution of this method. We examined a group of 20 healthy volunteers and a group of 16 volunteers who had a conduction disturbance in the anterior part of the visual pathway (shown with a prolongation of the latency P100 in the visual evoked potentials). The light stimulation was performed with a LED-goggle and a stimulation time each of 10 s "on" and "off" with a frequency of 15 Hz and constant light intensity. We found a reactive increase of the flow velocity of 16% in the control group. The increase begun after a latency of 1,4 s and 1s respectively in this cases who had an increase of flow velocity at the beginning of the flow response. The initial maximum was reached after 5,6 s. Flow velocity begun to decrease 2,9 s after end of light stimulation. There were no significant differences between both groups except for the latencies with increase of flow velocity at the beginning but without initial decrease. Our values were comparable to the values of other studies with similar experimental conditions. Similar patterns of the flow response were described except of the phenomen of the "initial undershoot". We discussed activation of other areas of the brain and a distribution of blood flow there as an explanation. The time resolution of the functional Doppler sonography is suitable to investigate the time course of the cerebral hemodynamic. But it is not sensitive enough to get conduction disturbances in the anterior part of the visual pathway. The method might be used to investigate disturbances in the neurovascular coupling.
28
Chung-Yi, Tsai, and 蔡鐘毅. "Color Response analysis by EEG and Visual Evoked Potential." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/51180691131319959968.
Full textAbstract:
碩士亞洲大學
數位媒體設計學系碩士班
99
The color, shape and size are main factors to people to define an object in daily life.The color of an object depends on both the physics of the object in its environment and the characteristics of the perceiving eye and brain. The colors result from neural responses in human’s visual neural systems, whose process and activities can be understood through human electroencephalogram (EEG). In terms of patterns, human perception of colors is influenced by patterns and sizes; patterns, colors and sizes bear close relations and interact with each other. Therefore, this study explored the reaction of EEG to visual stimuli aroused when people perceive combinations of different colors,patterns and sizes. The study results indicated that: (1) Different colors (R, G, B), different patterns (checkerboard, horizontal stripes, and concentric circles) and different size has significant effects on four peaks of EEG (N1、N2 latency and P1、P2 amplitude).(2) There has significant differences in EEG with higher P2 amplitude response of checkerboard and horizontal stripes by red color than the other two colors (checkerboard: red > blue > green; horizontal stripes: red > green > blue); for concentric circles, there was higher P2 amplitude response by blue color than green, the lowest was red color (blue > green> red).
29
Ramanna, Lakshmish. "Recording of cortical auditory evoked potentials on personal digital assistants /." 2008. http://proquest.umi.com/pqdweb?did=1654488281&sid=6&Fmt=2&clientId=10361&RQT=309&VName=PQD.
Full text
30
Boon, Mei Ying Optometry & Vision Science Faculty of Science UNSW. "Maturation of the transient chromatic (L-M) visual evoked potential: insights from linear and nonlinear analysis." 2007. http://handle.unsw.edu.au/1959.4/40653.
Full textAbstract:
Introduction: Psychophysical and electrophysiological techniques have shown that chromatic contrast sensitivity improves between infancy and adolescence. In adults, electrophysiological and psychophysical methods usually agree. However, in infants electrophysiological techniques may underestimate ability to see chromatic contrast (Suttle et al., 2002). It is not known if the discrepancy between electrophysiological and psychophysical methods continues during childhood nor whether the chromatic VEP can be used as an indicator of colour perception in children. Purpose: To investigate the transient L-M chromatic visual evoked potential and its ability to indicate perception (psychophysical thresholds) of chromatic stimuli in children and adults. In particular, to determine whether a discrepancy between VEP and psychophysical L-M thresholds exists during childhood and if so, to gain some understanding about the nature of the discrepancy. Methods: Transient chromatic VEPs were recorded in children (aged 4.5-13 years) and adults (aged 20-40 years). VEP thresholds were compared with psychophysical thresholds (within-subjects comparison). Because the VEPs of the children were less intra-individually repeatable in morphology than those of the adults, post-hoc objective analysis of the VEPs, linear (Fourier) and nonlinear dynamical (Grassberger and Procaccia's (1983) correlation dimension) analyses, was conducted. Results: VEP and psychophysical estimates of chromatic contrast thresholds agreed using a variety of methods in the adults. In the children, however, the objective methods of assessment (extrapolation from Fourier-derived amplitudes and the correlation dimension) were more accurate than the methods that employed subjective evaluations of VEP morphology. Conclusion: The L-M transient chromatic VEPs of both children (aged 4.5-13 years) and adults appear to contain chromatic information, even in the absence of repeatable VEP morphology and should therefore be able to indicate chromatic perception (psychophysical thresholds). However, the chromatic information may be present as a nonlinear dynamical signal, which may require objective methods (Fourier analysis, the correlation dimension) to reveal the chromatic signal. The greater intra-individual variability of VEP morphology in children compared to adults may reflect poorer precision when switching between cortical states in children's brains. Alternatively, interactions between the immature visual system of the children and their general EEG may occur. Children's VEPs should therefore be interpreted differently to adult VEPs.
31
MacDonald, John J. "Crossmodal interactions in stimulus-driven spatial attention and inhibition of return: evidence from behavioural and electrophysiological measures." Thesis, 1999. http://hdl.handle.net/2429/10165.
Full textAbstract:
Ten experiments examined the interactions between vision and audition in stimulusdriven
spatial attention orienting and inhibition of return (IOR). IOR is the demonstration that
subjects are slower to respond to stimuli that are presented at a previously stimulated location. In
each experiment, subjects made go/no-go responses to peripheral targets but not to central
targets. On every trial, a target was preceded by a sensory event, called a "cue," either in the
same modality (intramodal conditions) or in a different modality (crossmodal conditions). The
cue did not predict the location of the target stimulus in any experiment. In some experiments,
the cue and target modalities were fixed and different. Under these conditions, response times to
a visual target were shorter when it appeared at the same location as an auditory cue than when it
appeared on the opposite side of fixation, particularly at short (100 ms) cue-target stimulus onset
asynchronies (Experiments 1A and IB). Similarly, response times to an auditory target were
shorter when it appeared at the same location as a visual cue than when it appeared at a location
on the opposite side of fixation (Experiments 2A and 2B). These crossmodal effects indicate that
stimulus-driven spatial attention orienting might arise from a single supramodal brain
mechanism. IOR was not observed in either crossmodal experiment indicating that it might arise
from modality specific mechanisms. However, for many subjects, IOR did occur between
auditory cues and visual targets (Experiments 3A and 3B) and between visual cues and auditory
targets (Experiment 4A and 4B) when the target could appear in the same modality as the cue on
half of the trials. Finally, the crossmodal effects of stimulus-driven spatial attention orienting on
auditory and visual event-related brain potentials (ERPs) were examined in the final two
experiments. Auditory cues modulated the ERPs to visual targets and visual cues modulated the
ERPs to auditory targets, demonstrating that the mechanisms for spatial attention orienting
cannot be completely modality specific. However, these crossmodal ERP effects were very
different from each other indicating that the mechanisms for spatial attention orienting cannot be
completely shared.
32
Yovel, Galit. "Hemispheric asymmetry and interhemispheric communication in face perception /." 2001. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pqdiss&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:3029552.
Full text
33
Ruseckaite, Rasa. "Investigation of normal vision and neuro-ophthalmic disorders using nonlinear systems identification methods." Phd thesis, 2004. http://hdl.handle.net/1885/148468.
Full text
34
Leahan, K. E. "Photic stimulation and the treatment of mood and sleep disorders." Phd thesis, 2004. http://hdl.handle.net/1885/148546.
Full text
35
McFarlane, Michelle. "Poor Glycemic Control is Associated with Neuroretinal Dysfunction in Short-wavelength Cone Pathways of Adolescents with Type 1 Diabetes." Thesis, 2010. http://hdl.handle.net/1807/25855.
Full textAbstract:
Studies demonstrate short-wavelength cone pathway dysfunction in patients with diabetes and no clinically visible DR. Poor glycemic control, as measured by hemoglobin A1c (HbA1c), is a strong risk factor for DR. We hypothesized that raised HbA1c was associated with short-wavelength cone sensitive visual evoked potential (S-VEP) and electroretinogram (sERG) dysfunction.
Forty adolescents with diabetes and 39 controls were tested using the S-VEP. Latencies to a short-wavelength stimulus were delayed in patients at low contrasts. Patient S-VEP latencies were not associated with HbA1c when controlling for age and time since diagnosis. Twenty-one adolescents with diabetes and 19 controls were tested using the sERG. Implicit times of the b-wave were delayed but not associated with HbA1c when controlling for time since diagnosis.Patient PhNR amplitudes were reduced. A one-unit increase in HbA1c was associated with a 15% sERG PhNR amplitude reduction (p=0.004). The sERG PhNR may be a potential biomarker for DR.
36
Li, Qing Quan, and 李清泉. "Visually evoked startle responses in the tigerperch (terapon jarbua)." Thesis, 1994. http://ndltd.ncl.edu.tw/handle/76030197985483722931.
Full text