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1
Chambers, Christopher D. (Christopher David) 1977. "A psychophysical investigation of the octave illusion." Monash University, Dept. of Psychology, 2002. http://arrow.monash.edu.au/hdl/1959.1/8303.
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2
Best, Virginia Ann. "Spatial Hearing with Simultaneous Sound Sources: A Psychophysical Investigation." Thesis, The University of Sydney, 2004. http://hdl.handle.net/2123/576.
Full textAbstract:
This thesis provides an overview of work conducted to investigate human spatial hearing in situations involving multiple concurrent sound sources. Much is known about spatial hearing with single sound sources, including the acoustic cues to source location and the accuracy of localisation under different conditions. However, more recently interest has grown in the behaviour of listeners in more complex environments. Concurrent sound sources pose a particularly difficult problem for the auditory system, as their identities and locations must be extracted from a common set of sensory receptors and shared computational machinery. It is clear that humans have a rich perception of their auditory world, but just how concurrent sounds are processed, and how accurately, are issues that are poorly understood. This work attempts to fill a gap in our understanding by systematically examining spatial resolution with multiple sound sources. A series of psychophysical experiments was conducted on listeners with normal hearing to measure performance in spatial localisation and discrimination tasks involving more than one source. The general approach was to present sources that overlapped in both frequency and time in order to observe performance in the most challenging of situations. Furthermore, the role of two primary sets of location cues in concurrent source listening was probed by examining performance in different spatial dimensions. The binaural cues arise due to the separation of the two ears, and provide information about the lateral position of sound sources. The spectral cues result from location-dependent filtering by the head and pinnae, and allow vertical and front-rear auditory discrimination. Two sets of experiments are described that employed relatively simple broadband noise stimuli. In the first of these, two-point discrimination thresholds were measured using simultaneous noise bursts. It was found that the pair could be resolved only if a binaural difference was present; spectral cues did not appear to be sufficient. In the second set of experiments, the two stimuli were made distinguishable on the basis of their temporal envelopes, and the localisation of a designated target source was directly examined. Remarkably robust localisation was observed, despite the simultaneous masker, and both binaural and spectral cues appeared to be of use in this case. Small but persistent errors were observed, which in the lateral dimension represented a systematic shift away from the location of the masker. The errors can be explained by interference in the processing of the different location cues. Overall these experiments demonstrated that the spatial perception of concurrent sound sources is highly dependent on stimulus characteristics and configurations. This suggests that the underlying spatial representations are limited by the accuracy with which acoustic spatial cues can be extracted from a mixed signal. Three sets of experiments are then described that examined spatial performance with speech, a complex natural sound. The first measured how well speech is localised in isolation. This work demonstrated that speech contains high-frequency energy that is essential for accurate three-dimensional localisation. In the second set of experiments, spatial resolution for concurrent monosyllabic words was examined using similar approaches to those used for the concurrent noise experiments. It was found that resolution for concurrent speech stimuli was similar to resolution for concurrent noise stimuli. Importantly, listeners were limited in their ability to concurrently process the location-dependent spectral cues associated with two brief speech sources. In the final set of experiments, the role of spatial hearing was examined in a more relevant setting containing concurrent streams of sentence speech. It has long been known that binaural differences can aid segregation and enhance selective attention in such situations. The results presented here confirmed this finding and extended it to show that the spectral cues associated with different locations can also contribute. As a whole, this work provides an in-depth examination of spatial performance in concurrent source situations and delineates some of the limitations of this process. In general, spatial accuracy with concurrent sources is poorer than with single sound sources, as both binaural and spectral cues are subject to interference. Nonetheless, binaural cues are quite robust for representing concurrent source locations, and spectral cues can enhance spatial listening in many situations. The findings also highlight the intricate relationship that exists between spatial hearing, auditory object processing, and the allocation of attention in complex environments.
3
Seton, John Christopher. "A psychophysical investigation of auditory rhythmic beat perception." Thesis, University of York, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.329671.
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4
Lee, Suzanne E. "An investigation of team lifting using psychophysical methods." Thesis, Virginia Tech, 1995. http://hdl.handle.net/10919/42550.
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Lifting is one of the major causes of back injury in the workplace. Often, workers are told to ask for the help of another worker when the load is too great to be lifted alone, yet the effects of these team lifts have not been researched until recently. This experiment investigated some of the variables which may affect the results of team lifting tasks. The psychophysical methodology has been used for almost 30 years in trying to determine the maximum acceptable weight of lift for industrial workers. Though two previous studies of team lifting used the psychophysical approach, no effort was made to identify and control variables which may affect team tasks. This experiment manipulated two variables, box type (double or single) and isolation condition (curtains open or closed) to see whether these would produce the psychosocial effects of social loafing and social facilitation. Three male and three female two-person teams performed team lifts, using psychophysical methodology, under all four conditions.
The only significant effect found was for gender. Female teams lifted 58.8% of the mass the male teams lifted. Male teams lifted 92.5% and female teams 87.8% of the sum of their individual lifts. This is in close agreement with other studies of team lifting. A regression model was developed in order to predict the amount of weight a team can lift, with an R2 of 0.962. The external validity of the task conditions was also investigated.Master of Science
5
Lee, Suzanne Elin. "An investigation of team lifting using psychophysical methods /." This resource online, 1995. http://scholar.lib.vt.edu/theses/available/etd-05092009-040526/.
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6
Morioka, Miyuki. "Psychophysical investigation of the perception of hand-transmitted vibration." Thesis, University of Southampton, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.484260.
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7
Doney, A. C. F. "A psychophysical investigation of the visual motion processing system." Thesis, University of York, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.372774.
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8
Roff, Emma J. "Topographic, haemodynamic and psychophysical investigation of glaucomatous optic neuropathy." Thesis, Aston University, 1999. http://publications.aston.ac.uk/14554/.
Full textAbstract:
Loss of optic nerve head (ONH) axons in primary open angle glaucoma (POAG) has been attributed to both mechanical and vascular factors. Confocal scanning laser ophthalmoscopy (cSLO) provides a promising tool for the topographic follow-up of the ONH in glaucoma, while scanning laser Doppler flowmetry (SLDF) facilitates the rapid non-invasive assessment of retinal capillary blood flow. The purposes of these investigations were to optimise the techniques and explore their potential to classify and monitor disease. Preliminary investigations explored the reproducibility and validity of cSLO and SLDF and showed that: For cSLO: In a model eye, measurements are accurate over a range of axial lengths. For best reproducibility, seven images per visit are required, with a contour line located on Elschnig's scleral ring and transferred automatically between images. For SLDF: Three perfusion images are required for optimum reproducibility. Physiological changes induced by gas perturbation can be measured. Cross-sectional comparison of groups of normal subjects and early POAG patients showed that: cSLO parameters differentiate the early POAG group. Blood volume measured by SLDF showed group differences in superior nasal retina only. Longitudinal investigation of ONH topography, haemodynamic and visual field indices in normal subjects and POAG patients showed that: cSLO detects topographical change over time more frequently in the POAG group. Important parameters include: C:D area ratio, cup and rim area, mean depth in contour, volumes above and below reference and surface. Factor analysis identified "cup" and "rim" factors that can be used to detect change over time in individual patients. Blood flow changes were most apparent in the inferior nasal peripapillary retina of the POAG group. Perimetry is of clinical value for the identification of glaucoma but is less sensitive than cSLO for monitoring glaucomatous change.
9
Best, Virginia Ann. "Spatial Hearing with Simultaneous Sound Sources: A Psychophysical Investigation." University of Sydney. Medicine, 2004. http://hdl.handle.net/2123/576.
Full textAbstract:
This thesis provides an overview of work conducted to investigate human spatial hearing in situations involving multiple concurrent sound sources. Much is known about spatial hearing with single sound sources, including the acoustic cues to source location and the accuracy of localisation under different conditions. However, more recently interest has grown in the behaviour of listeners in more complex environments. Concurrent sound sources pose a particularly difficult problem for the auditory system, as their identities and locations must be extracted from a common set of sensory receptors and shared computational machinery. It is clear that humans have a rich perception of their auditory world, but just how concurrent sounds are processed, and how accurately, are issues that are poorly understood. This work attempts to fill a gap in our understanding by systematically examining spatial resolution with multiple sound sources. A series of psychophysical experiments was conducted on listeners with normal hearing to measure performance in spatial localisation and discrimination tasks involving more than one source. The general approach was to present sources that overlapped in both frequency and time in order to observe performance in the most challenging of situations. Furthermore, the role of two primary sets of location cues in concurrent source listening was probed by examining performance in different spatial dimensions. The binaural cues arise due to the separation of the two ears, and provide information about the lateral position of sound sources. The spectral cues result from location-dependent filtering by the head and pinnae, and allow vertical and front-rear auditory discrimination. Two sets of experiments are described that employed relatively simple broadband noise stimuli. In the first of these, two-point discrimination thresholds were measured using simultaneous noise bursts. It was found that the pair could be resolved only if a binaural difference was present; spectral cues did not appear to be sufficient. In the second set of experiments, the two stimuli were made distinguishable on the basis of their temporal envelopes, and the localisation of a designated target source was directly examined. Remarkably robust localisation was observed, despite the simultaneous masker, and both binaural and spectral cues appeared to be of use in this case. Small but persistent errors were observed, which in the lateral dimension represented a systematic shift away from the location of the masker. The errors can be explained by interference in the processing of the different location cues. Overall these experiments demonstrated that the spatial perception of concurrent sound sources is highly dependent on stimulus characteristics and configurations. This suggests that the underlying spatial representations are limited by the accuracy with which acoustic spatial cues can be extracted from a mixed signal. Three sets of experiments are then described that examined spatial performance with speech, a complex natural sound. The first measured how well speech is localised in isolation. This work demonstrated that speech contains high-frequency energy that is essential for accurate three-dimensional localisation. In the second set of experiments, spatial resolution for concurrent monosyllabic words was examined using similar approaches to those used for the concurrent noise experiments. It was found that resolution for concurrent speech stimuli was similar to resolution for concurrent noise stimuli. Importantly, listeners were limited in their ability to concurrently process the location-dependent spectral cues associated with two brief speech sources. In the final set of experiments, the role of spatial hearing was examined in a more relevant setting containing concurrent streams of sentence speech. It has long been known that binaural differences can aid segregation and enhance selective attention in such situations. The results presented here confirmed this finding and extended it to show that the spectral cues associated with different locations can also contribute. As a whole, this work provides an in-depth examination of spatial performance in concurrent source situations and delineates some of the limitations of this process. In general, spatial accuracy with concurrent sources is poorer than with single sound sources, as both binaural and spectral cues are subject to interference. Nonetheless, binaural cues are quite robust for representing concurrent source locations, and spectral cues can enhance spatial listening in many situations. The findings also highlight the intricate relationship that exists between spatial hearing, auditory object processing, and the allocation of attention in complex environments.
10
Morris, Eilon. "VIA RHYTMÓS : an investigation of rhythm in psychophysical actor training." Thesis, University of Huddersfield, 2013. http://eprints.hud.ac.uk/id/eprint/17541/.
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This thesis investigates the significance of rhythm to the actor, examining the ways it is approached, understood and embodied within a range of training practices. In what ways does rhythm facilitate and transform the practices of individual performers and ensembles, affecting their use of attention, physical coordination, qualities of connectivity, states of consciousness and emotions? The psychophysical mechanisms through which rhythm informs these key aspects of actor training are analysed here via a range of contemporary and historical psychophysical and cultural frameworks. Drawing on this body of research this thesis argues the case for a greater understanding of the pedagogy of rhythm within actor training, indicating a number of areas for further investigation and potential developments within this field. Beginning with Stanislavski’s use of “Tempo-rhythm” and progressing through the practices of Meyerhold and Grotowski, a number of key rhythmic principles will be discussed. This will lead on to a series of case studies on the contemporary training practices of John Britton, Nicolás Núñez, and Reinhard Flatischler. Following this will be an examination of simultaneity in acting practices and an analysis of the author’s own practical research into the use of polyrhythm as a tool for cultivating modes of simultaneous attention and action in actor training.
11
May, Keith A. "Edge coding in human vision: a psychophysical and computational investigation." Thesis, Aston University, 2003. http://publications.aston.ac.uk/14560/.
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This thesis presents a study of how edges are detected and encoded by the human visual system. The study begins with theoretical work on the development of a model of edge processing, and includes psychophysical experiments on humans, and computer simulations of these experiments, using the model. The first chapter reviews the literature on edge processing in biological and machine vision, and introduces the mathematical foundations of this area of research. The second chapter gives a formal presentation of a model of edge perception that detects edges and characterizes their blur, contrast and orientation, using Gaussian derivative templates. This model has previously been shown to accurately predict human performance in blur matching tasks with several different types of edge profile. The model provides veridical estimates of the blur and contrast of edges that have a Gaussian integral profile. Since blur and contrast are independent parameters of Gaussian edges, the model predicts that varying one parameter should not affect perception of the other. Psychophysical experiments showed that this prediction is incorrect: reducing the contrast makes an edge look sharper; increasing the blur reduces the perceived contrast. Both of these effects can be explained by introducing a smoothed threshold to one of the processing stages of the model. It is shown that, with this modification,the model can predict the perceived contrast and blur of a number of edge profiles that differ markedly from the ideal Gaussian edge profiles on which the templates are based. With only a few exceptions, the results from all the experiments on blur and contrast perception can be explained reasonably well using one set of parameters for each subject. In the few cases where the model fails, possible extensions to the model are discussed.
12
Hattenberger, Timothy John. "A psychophysical investigation of global illumination algorithms used in augmented reality /." Link to online version, 2006. https://ritdml.rit.edu/dspace/handle/1850/1541.
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13
Hotchkiss, John. "A psychophysical investigation of audio-visual timing in the millisecond range." Thesis, University of Bradford, 2012. http://hdl.handle.net/10454/5771.
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The experiments described in this thesis use psychophysical techniques and human observers to investigate temporal processing in the millisecond range. The thesis contains five main sections. Introductory chapters provide a brief overview of the visual and auditory systems, before detailing our current understanding of duration processing. During the course of this review, several important questions are highlighted. The experiments detailed in Chapters 8-11 seek to address these questions using the psychophysical techniques outlined in Chapter 7. The results of these experiments increase our understanding of duration perception in several areas. Firstly, Experiments 1 and 2 (Chapter 8) highlight the role of low level stimulus features: even when equated for visibility stimuli of differing spatial frequency have different perceived durations. Secondly, a psychophysical hypothesis arising from the 'duration channels' or 'labelled lines' model of duration perception is given strong support by the adaptation experiments detailed in Chapter 9 and 10. Specifically, adaptation to durations of a fixed temporal extent induces repulsive duration aftereffects that are sensory specific and bandwidth limited around the adapted duration. Finally Chapter 11 describes the results of experiments designed to probe the processing hierarchy within duration perception by measuring the interdependency of illusions generated via duration adaptation and via multisensory cue combination. The results of these experiments demonstrate that duration adaptation is a relatively early component of temporal processing and is likely to be sub served by duration selective neurons situated in early sections of the visual and auditory systems.
14
Love, Scott. "An fMRI and psychophysical investigation of the temporal factor of audiovisual integration." Thesis, University of Glasgow, 2011. http://theses.gla.ac.uk/3578/.
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Our world is multisensory! To function and survive in our environment we utilise all of the cross-modal sensory information available to us. Some of it may be redundant but that simply makes our decisions more reliable (e.g., Clark and Yuille, 1990; Landy et al., 1995; Ernst and Banks, 2002). Knowledge of multisensory processes, which make use of this multitude of rich cross-modal information, is growing rapidly (for a review see, Calvert et al., 2004) and changing the way both philosophers (e.g., Macpherson, 2011) and scientists (e.g., Driver and Spence, 2000) think about perception and the senses. One of the main challenges faced by this research field is how to decide which types of evidence are sufficient to prove that multisensory integration has occurred (e.g., Stein et al., 2009). To make things more complicated, the solution will be different dependent on whether integration is investigated at the neuronal, cerebral or behavioural level. Chapter 2 of this thesis provides new evidence about the integration criteria generally used in functional magnetic resonance imaging (fMRI). The choice of criteria had an obvious influence on which regions were found to integrate audiovisual information from the face and voice. Raising the question, which of these criteria should be used? Our conclusion was that it would be prudent to investigate the results of all of these criteria and; moreover, that a more cogent method of investigation would be to combine these criteria with manipulations of stimulus signal-to-noise ratio and/or congruency. At the level of the neuron we know that the relative temporal synchrony of cross-modal cues can be an important factor in determining whether the neuron displays a multisensory response or not (e.g., Stein and Meredith, 1993). Manipulating temporal synchrony is actually one of the main techniques that researchers have used to explore multisensory processes at the neuronal, cerebral and behavioural levels (see relevant chapters in, Calvert et al., 2004). The experiments presented in Chapters 3, 4 and 5 of the current thesis focus on this temporal factor of audiovisual integration: the synchrony perception process in particular. Chapters 3 and 4 present new evidence that two of the main experimental tasks used to investigate the synchrony perception process should not be used interchangeably. The experiments in those chapters asked participants to make both synchrony judgments (SJs) and temporal order judgments (TOJs) to identical audiovisual stimuli with various levels of cue asynchrony. First, Chapter 3 provided further evidence (Fujisaki and Nishida, 2009; van Eijk et al., 2008; Vatakis et al., 2008b; Vroomen and Stekelenburg, 2011) that these two tasks differ at the behavioural level. Second, Chapter 4 gave further credence to these behavioural results by using fMRI to localise, for the first time, the different neural correlates of these two tasks. Moving beyond localisation of function, Chapter 5 outlines a fMRI experiment, which explored the role that different brain regions play in the synchrony perception process. Participants performed a SJ task to a large set of asynchronous audiovisual speech stimuli. Networks of regions responding preferentially to either synchronous or asynchronous audiovisual speech stimuli were found. However, which regions comprised these networks and whether they were both localised was dependent on which asynchronous conditions were included in contrasts of interest. This indicates that differences in stimulus and contrast choice in previous research could have helped produce inconsistencies in results (Stevenson et al., 2010).
15
Hanson, James Vincent Michael. "The perceived timing of events across different sensory modalities : a psychophysical investigation of multisensory time perception in humans." Thesis, University of Bradford, 2009. http://hdl.handle.net/10454/4290.
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The experiments reported within this thesis use psychophysical techniques to examine the factors which determine perceived multisensory timing in humans. Chapters 1 and 2 describe anatomical and psychophysical features of temporal processing, respectively, whilst Chapter 3 introduces the reader to psychophysical methods. Chapter 4 examines the relationship between two measures of sensory latency, reaction time (RT) and crossmodal temporal order judgment (TOJ). Despite task and attentional manipulations the two measures do not correlate, suggesting that they measure some fundamentally different aspect(s) of temporal perception. Chapter 5 examines the effects of adaptation to asynchronous stimulus pairs on perceived audiovisual (AV), audiotactile (AT) and visuotactile (VT) temporal order. Significant temporal shifts are recorded in all three conditions. Evidence is also presented showing that crossmodal TOJs are intransitive. Chapter 6 shows that concurrent adaptation to two sets of asynchronous AV stimulus pairs causes perceived AV temporal order to recalibrate at two locations simultaneously, and that AV asynchrony adaptation effects are significantly affected by observers' attention during adaptation. Finally, Chapter 7 shows that when observers are accustomed to a physical delay between motor actions and sensory events, an event presented at a reduced delay appears to precede the causative motor action. The data are well-described by a simple model based on a strong prior assumption of physical synchrony between motor actions and their sensory consequences.
16
Mauney, Daniel W. "Psychophysical investigation of the real-ear attenuation of hearing protection devices under different sound-field diffusivity conditions." Thesis, Virginia Tech, 1991. http://hdl.handle.net/10919/41690.
Full textAbstract:
Certain U. S. and international consensus standards governing hearing protection device (HPD) attenuation testing specify the use of a diffuse sound field to ensure the sound field remains uniform and random-incidence in an envelope about the subject’s head (ANSI, 1974; ANSI, 1984; British BSI 5108:1983; Canadian CSA Z94.2-M1984; ISO 4869- 1:1990; Swedish SS 882151). However, there are very few experimental data to support these restrictive requirements. The research presented herein investigated this issue by applying three different environments in tests of the attenuation of four different hearing protectors (three earmuffs and one earplug) at each of nine 1/3 octave band frequencies centered at 125, 250, 500, 1000, 2000, 3150, 4000, 6300, and 8000 Hz. One testing environment comprised a reverberant room with three loudspeakers, one firing in each room plane, that met all the specifications for testing under ANSI S3.19-1974 (ANSI, 1974). The other two environments progressively degraded the diffusivity of the sound field through the use of a single loudspeaker and room surface treatment with absorptive panels. A psychophysical real-ear-attenuation-at-threshold procedure was used to obtain attenuation data. The results showed small, but statistically significant, differences in attenuation among the three environments for specific test frequencies. Due to their statistical significance, these differences preclude direct comparison of attenuation data obtained in these different environments, especially when the data are used for purposes such as technical design research, product comparison and/or labeling, and testing standards development. However, being of small magnitude, these differences are not great enough to prevent obtaining an estimation of the attenuation that an individual is achieving with a particular device under these alternative environments. With this in mind, the use of an industrial audiometric test booth may be beneficial for determining an individual worker’s protection levels actually achieved on the job. In sum, the interpretation of the results differs depending upon the intended purpose of the testing.Master of Science
17
Skinner, Fiona K. "Dopamine and visual function in schizophrenia : a psychophysical investigation using the tilt after-effect and contrast sensitivity tests." Thesis, University of Aberdeen, 1994. http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU068528.
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The study used a non-invasive technique, the Tilt Aftereffect (TAE) test, to investigate the visual changes influenced by dopamine (DA) in schizophrenia. One-third of forty five schizophrenic patients could not complete the TAE test and this group was found to have impaired sustained attention and to have different demographic and clinical characteristics from the schizophrenic patients who could complete the TAE test. TAE changes were found only in response to DA changes brought about by altering neuroleptic levels, e.g. 'before' compared with 'after' a depot injection. These changes were only found when gratings of 2 c/d were used and not for 10 c/d. No illness or drug effect was found using the TAE test. A similarity in the pattern of change over time was found for the TAE test using 2 c/d gratings and the peak spatial frequency (SF) from the Contrast Sensitivity (CS) test in response to changes in levels of DA. A decrease in DA caused a shift of the CS peak to lower SFs, with a decrease in sensitivity for mid to high SFs (3 - 10 c/d) and an increase in sensitivity for low SFs (0.5, 1 c/d). The findings suggest that both the TAE and CS tests are influenced by DA and that lateral inhibition alone cannot explain the production of the TAE since the influence of the orientation of the adapting gratings on the size of the TAE indicates that an adaptation process is involved. It is suggested that the transient system, which is sensitive to low spatial and high temporal frequencies, may be selectively affected by DA changes.
18
Bosworth, Rain G. "Psychophysical investigation of visual perception in deaf and hearing adults : effects of auditory deprivation and sign language experience /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC IP addresses, 2001. http://wwwlib.umi.com/cr/ucsd/fullcit?p3015850.
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Mauney, Daniel W. "Investigation of physical and psychophysical methods for the attenuation measurement of circumaural hearing protectors with implication for field use." Diss., Virginia Tech, 1994. http://hdl.handle.net/10919/40073.
Full textAbstract:
A field-implementable measure is needed to estimate the attenuation workers are
achieving with their hearing protectors in the field. Alternative measures for assessing a
hearing protector's effectiveness were evaluated through comparison to the standardized
real-ear attenuation at threshold (REAT) method, termed 1I3-REAT, a psychophysical
procedure (ANSI S3.19-1984). One alternative deviated from the standardized procedure
primarily through utilizing a pure-tone audiometer coupled to an amplifier and loudspeaker
for the sound field presentation of pure tones (Pr -REAT). The other alternative. tenned
microphone in real-ear (MIRE), used miniature microphones in each concha and just
outside of each of the subject's two ears to physically measure the attenuation of the
protector using both insertion loss (lL-MIRE) and noise reduction (NR-MIRE) procedures.
Comparisons between the alternative measures were made across nine 113 octave bands
centered at 125, 250, 500, 1000, 2000, 3150,4000, 6300, and 8000 Hz. The experiment
also explored a means for predicting broadband attenuation from data of a single 113 octave
band through a regression analysis for both PT -REAT tests and NR-MIRE tests.
Results showed that when comparing the PT -REAT test and the standardized 1/3-
REA T method, the standardized method exhibited significantly greater attenuation at most
of the 1/3 octave bands tested. The difference, however, may be due to the higher ambient
noise levels present in the pure tone condition. The MIRE measures also showed some
significant differences with the standardized 1/3-REAT method for the values collapsed
across protectors, with the direction of the difference changing with test band. At 125 Hz,
the MIRE metrics yielded significantly lower attenuation, while from 500 to 6300 Hz, the
1/3-REAT method generally yielded significantly lower attenuation. These differences may
be due in part to the occlusion effect and the bone conduction of sound. In general,
however, the size and consistency of the differences across hearing protection devices
(HPDs) suggest that PT-REAT and MIRE measures hold promise for providing quick and
relatively accurate estimations of an HPD's attenuation in the field. Results of the
regression analyses indicated that single test band data obtained at 250 and 500 Hz, from
both PT-REAT and NR-MIRE metrics, provided the best predictions for the hearing
protectors tested in this study, based on their Pearson product-moment correlation
coefficients.Ph. D.
20
Vidmark, Jessica Sofie Louise. "An investigation of the relationships between electrotactile stimulus parameters, primary afferent response, and perceived sensation." Thesis, KTH, Skolan för kemi, bioteknologi och hälsa (CBH), 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-251735.
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Sensory feedback possesses the possibility of adding a new dimension to many applications, including, but not limited to, prosthetics and surgical robots for improved control, virtual reality for incorporation of another sense, and phantom limb pain reduction for amputees. Electrotactile stimulation provides a compact, light-weight, energy efficient, highly responsive, and non-invasive option for sensory feedback; however, it has been found to commonly elicit unnatural or uncomfortable sensations for the user. To address this issue, this thesis was designed to test the impact of the different electrotactile stimulus parameters – current amplitude and polarity, pulse width, frequency, and waveform – on the user’s perceived sensation and afferent neural response. The relationship between sensation and neural response was also analysed. The aim of this thesis was to create guidelines to assist in the design and use of electrotactile stimulation. Neural data and matching psychophysical data from one healthy subject and purely psychophysical data from three others were gathered while applying electrotactile stimulations of different parameter combinations on the dorsal side of the hand or lower arm. Significant (p < 0.05) correlations and differences were found in all three relationships between electrotactile stimulus parameters, primary afferent response, and perceived sensation. Current (specifically negative) or pulse width control in monophasic waveforms were deemed most appropriate in applications that relay information through varying intensity. However, monophasic waveforms produced more discomfort, rendering biphasic waveforms more suitable when mild, local, and more natural sensations are of greater importance. Surprisingly, the data also suggested higher sensitivity to positive currents. While lower values of current amplitude and pulse width increased neural spike count, stimulus frequency could reliably control neural firing at all tested frequencies. Spike counts were moderately to strongly correlated with perceived intensity; however, practically identical neural responses could elicit different sensations. High current pulses at low frequencies induced spikes with the shortest latency – but with greater risk of discomfort. Due to limitations in sample size, generalisability is limited, and this thesis should be considered a pilot study to guide future investigations. The results suggest that recording from single and multiple afferent nerve fibres simultaneously would improve the understanding of the neural population response to electrotactile stimuli. Moreover, the one-to-one neural response to electrotactile stimuli raised the question of whether an electrotactile stimulation based on a natural spike pattern could replicate the original sensation. A future study testing this hypothesis may find a new approach to designing painless electrotactile stimulations for sensory feedback use.Sensorisk återkoppling har möjlighet att drastiskt förbättra många användningsområden, t.ex. genom att bidra till enklare kontroll av proteser och kirurgiska robotar, mer verklighetstrogna VR-spel, och minskade fantomsmärtor hos patienter med amputeringar. Elektrisk hudstimulering erbjuder ett kompakt, lätt, energisnålt, hög-responsivt och icke-invasivt alternativ för sensorisk återkoppling – dock framkallar denna metod ofta onaturliga och obehagliga förnimmelser för användaren. Detta examensarbete bemöter detta problem genom att undersöka effekten av stimuleringsparametrar som strömstyrka, pulsbredd, frekvens och vågform på försökspersonens upplevda förnimmelse samt den afferenta nervresponsen. Även relationen mellan förnimmelse och nervrespons analyserades. Examensarbetets ändamål var att skapa riktlinjer för att förenkla designen och användandet av elektrisk hudstimulering. Nervdata med matchande psykofysiska data samlades från en frisk försöksperson, samt enbart psykofysiska data från tre andra, under olika elektriska hudstimuleringar (med varierande parametervärden) på handens dorsala sida eller på underarmen. Signifikanta (p < 0.05) korrelationer och skillnader fanns i alla tre relationer mellan parametrarna för elektrisk hudstimulering, primärafferent respons och upplevd förnimmelse. Kontroll av ström (i synnerhet negativ) eller pulsbredd i monofasisk vågform visade sig vara mest fördelaktigt i applikationer där information kommuniceras till användaren genom att variera den upplevda intensiteten. Dock skapade denna vågform mer obehag, och bifasiska vågformer bedömdes mer passande då milda, lokala, och mer naturliga förnimmelser är av högre värde. Positiv ström upplevdes, förvånande, starkare än negativ. Vid låga värden på ström och pulsbredd var dessa faktorer viktiga gällande antalet aktionspotentialer (AP), men stimuleringsfrekvensen kunde kontrollera antalet AP vid alla frekvenser. Mängden AP var måttligt till starkt korrelaterad med upplevd intensitet – samtidigt kunde praktiskt taget identiska nervresponser vara kopplade till olika förnimmelser. Lågfrekvent stimulering med hög ström hade kortast latenstid, men högre risk för obehag. P.g.a. lågt antal försökspersoner är generaliserbarheten begränsad och detta examensarbete bör beaktas som en förstudie för att guida framtida forskning. Resultaten från denna studie antyder att en tydligare bild av populationsresponsen skulle kunna skapas genom samtidig läsning av ett flertal enskilda nervfibrer samtidigt. Det faktum att varje stimulering kunde ge upphov till en AP väckte frågan: kan ett stimuleringsmönster baserat på en naturlig nervrespons återskapa den ursprungliga förnimmelsen? En studie som testar denna hypotes har möjligheten att finna ett nytt tillvägagångssätt för att skapa smärtfri elektrisk hudstimulering för sensorisk återkoppling.
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Ragert, Patrick. "Investigation of the relation between perceptual changes and cortical reorganization within the somatosensory cortex through passive stimulation protocols and modified use a psychophysical and neurophysiological study in humans /." [S.l.] : [s.n.], 2004. http://deposit.ddb.de/cgi-bin/dokserv?idn=974108294.
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Nemes, Vanda Agnes. "A psychophysical investigation of human visual perceptual memory : a study of the retention of colour, spatial frequency and motion visual information by human visual short term memory mechanisms." Thesis, University of Bradford, 2011. http://hdl.handle.net/10454/5695.
Full textAbstract:
The aim of this thesis was to investigate how visual information is organised in perceptual short term memory, with special interest in colour, spatial frequency and velocity. Previous studies of VSTM have indicated the existence of specific memory mechanisms for visual attributes such as orientation, spatial frequency, velocity, contrast and colour. The retention of information in visual short term memory for these basic visual attributes can be disrupted by the presentation of masking stimuli during inter-stimulus intervals (ISIs), which are outside the range of traditional sensory masking. We exploited this memory masking effect in order to examine the organisation of visual information in VSTM. Four groups of experiments were conducted in which participants carried out a delayed discrimination paradigm that employed a two-alternative forced choice (2-AFC) procedure in conjunction with a method of constant stimuli. The fidelity of VSTM was measured by performance markers such as discrimination thresholds and point of subjective equalities. We have found selective memory masking effects, which serve as further evidence in favour of the modular organisation in VSTM, namely, that human visual perceptual memory is based upon multiple, tuned channels in case of colour, spatial frequency and speed, similar to those found in the earliest stages of visual processing for spatial frequency. Moreover, each of these storage mechanisms are tuned to a relatively narrow range of stimulus parameters that are closely linked to visual discrimination mechanisms. These findings add further support to the view that low-level sensory processing mechanisms form the basis for the retention of colour, spatial frequency and velocity information in perceptual memory. We also found evidence for the broad range of transfer of memory masking effects across spatial location, which indicates more long range, long duration interactions between channels that are likely to rely upon contributions from neural processes located in higher visual areas. In conclusion, the experiments presented in this thesis provide significant insight into the organization of visual information in perceptual short term memory.
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Nemes, Vanda A. "A psychophysical investigation of human visual perceptual memory. A study of the retention of colour, spatial frequency and motion visual information by human visual short term memory mechanisms." Thesis, University of Bradford, 2011. http://hdl.handle.net/10454/5695.
Full textAbstract:
The aim of this thesis was to investigate how visual information is organised in
perceptual short term memory, with special interest in colour, spatial frequency
and velocity. Previous studies of VSTM have indicated the existence of specific
memory mechanisms for visual attributes such as orientation, spatial frequency,
velocity, contrast and colour. The retention of information in visual short term
memory for these basic visual attributes can be disrupted by the presentation of
masking stimuli during inter-stimulus intervals (ISIs), which are outside the
range of traditional sensory masking. We exploited this memory masking effect
in order to examine the organisation of visual information in VSTM. Four groups
of experiments were conducted in which participants carried out a delayed
discrimination paradigm that employed a two-alternative forced choice (2-AFC)
procedure in conjunction with a method of constant stimuli. The fidelity of VSTM
was measured by performance markers such as discrimination thresholds and
point of subjective equalities. We have found selective memory masking effects,
which serve as further evidence in favour of the modular organisation in VSTM,
namely, that human visual perceptual memory is based upon multiple, tuned
channels in case of colour, spatial frequency and speed, similar to those found
in the earliest stages of visual processing for spatial frequency. Moreover, each
of these storage mechanisms are tuned to a relatively narrow range of stimulus
parameters that are closely linked to visual discrimination mechanisms. These
findings add further support to the view that low-level sensory processing
mechanisms form the basis for the retention of colour, spatial frequency and
velocity information in perceptual memory. We also found evidence for the
broad range of transfer of memory masking effects across spatial location,
which indicates more long range, long duration interactions between channels
that are likely to rely upon contributions from neural processes located in higher
visual areas. In conclusion, the experiments presented in this thesis provide
significant insight into the organization of visual information in perceptual short
term memory.Federation of Ophthalmic and Dispensing Opticians
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Latham, Keziah J. C. "Psychophysical investigations of human peripheral vision." Thesis, Aston University, 1995. http://publications.aston.ac.uk/14598/.
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This thesis investigates various aspects of peripheral vision, which is known not to be as acute as vision at the point of fixation. Differences between foveal and peripheral vision are generally thought to be of a quantitative rather than a qualitative nature. However, the rate of decline in sensitivity between foveal and peripheral vision is known to be task dependent and the mechanisms underlying the differences are not yet well understood. Several experiments described here have employed a psychophysical technique referred to as 'spatial scaling'. Thresholds are determined at several eccentricities for ranges of stimuli which are magnified versions of one another. Using this methodology a parameter called the E2 value is determined, which defines the eccentricity at which stimulus size must double in order to maintain performance equivalent to that at the fovea. Experiments of this type have evaluated the eccentricity dependencies of detection tasks (kinetic and static presentation of a differential light stimulus), resolution tasks (bar orientation discrimination in the presence of flanking stimuli, word recognition and reading performance), and relative localisation tasks (curvature detection and discrimination). Most tasks could be made equal across the visual field by appropriate magnification. E2 values are found to vary widely dependent on the task, and possible reasons for such variations are discussed. The dependence of positional acuity thresholds on stimulus eccentricity, separation and spatial scale parameters is also examined. The relevance of each factor in producing 'Weber's law' for position can be determined from the results.
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Hubbard, Edward M. "Psychophysical and neuroimaging investigations of synesthesia /." Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 2004. http://wwwlib.umi.com/cr/ucsd/fullcit?p3148258.
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Chen, Xianze. "Six DOF tactile stimulator for psychophysical investigations." Thesis, McGill University, 1993. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=69787.
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The design of a high performance tactile stimulator with six degrees of freedom for psychometric investigations is the subject of this thesis.In order to design this device, a new mechanism is put forward, which is fully parallel and string driven. It achieves kinematic and dynamic isotropy. From the kinematic and dynamic analysis, the conditions for obtaining the best performance results are derived. These form the basis for the design and lead to a high performance device, which has wide bandwidth, low friction and which is free from backlash. The input and output is fully decoupled, which lead to simple control.
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Ripamonti, Caterina. "Computational and psychophysical investigations of perceptual transparency." Thesis, University of Derby, 2002. http://hdl.handle.net/10545/324831.
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The work presented in this thesis has investigated, both computationally and psychophysically, the chromatic conditions for the phenomenon of perceptual transparency. A series of physical measurements and numerical simulations have been carried out to show that the cone-excitation ratios between two opaque surfaces and the cone-excitation ratios between the same surfaces covered by a transparent filter are almost statistically invariant (see also Westland & Ripamonti, 2000) for many physically transparent systems. The relationship between physical transparency and perceptual transparency has been explored and strong psychophysical evidence has been presented to show that, when the invariance holds, the filter is perceived as transparent. Furthermore, the degree of invariance seems to be a good measure of the degree of perceived transparency. The more invariant the cone-excitation ratios are, the more the filter is perceived to be transparent. This shows that perceptual transparency is not a categorical perception but rather a continuously graded perception: the more the cone-excitation ratios approximate invariance the more the filtered area is perceived to be transparent. A set of further psychophysical experiments has been carried out to ascertain whether the invariance is required for all three classes of cones or whether some cone classes are more important than others. The data seem to support the notion that the S-cone class responses contribute relatively little to transparency perception. The role of image complexity on transparency perception was also explored. Specifically it has been shown that the strength of the transparency percept increases with the number of patches in a Mondrian display partially covered by a transparent filter. Finally, it is acknowledged that the chromatic conditions for transparency perception that are defined by the invariance model may well be alternatively expressed by other models or transparency or at other levels of visual processing. However, the invariance model makes explicit an intriguing link between transparency perception and colour constancy.
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Brady, Mark James. "Psychophysical investigations of incomplete forms and forms with background /." Diss., ON-CAMPUS Access For University of Minnesota, Twin Cities Click on "Connect to Digital Dissertations", 1999. http://www.lib.umn.edu/articles/proquest.phtml.
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Varghese, Lenny Alex. "Psychophysical and electrophysiological investigations into the mechanisms supporting everyday communication." Thesis, Boston University, 2013. https://hdl.handle.net/2144/11074.
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Thesis (Ph.D.)--Boston UniversityHumans solve the so-called "cocktail party problem" with relative ease, and are generally able to selectively direct their attention to process and recall acoustic information from one sound source in the presence of other irrelevant stimuli that are competing for cognitive resources. This ability depends on a variety of factors, including volitional control of selective attention, the ability to store information in memory for recall at a later time, and the ability to integrate information across multiple sensory modalities. Here, psychophysical and electroencephalography (EEG) experiments were conducted to study these three factors. The effects of selective attention on cortical and subcortical structures were examined using EEG recorded during a dichotic listening task. Cortical potentials showed robust effects of attention (demonstrated by the ability to classify responses to attended and ignored speech based on short segments of EEG responses); however, potentials originating in the brainstem did not, even though stimuli were engineered to maximize the separability of the neural representation of the competing sources in the auditory periphery and thus the possibility of seeing attention-specific modulation of subcortical responses. In another study, the relationship between object formation and memory processing was explored in a psychophysical experiment examining how sequences of nonverbal auditory stimuli are stored and recalled from short-term memory. The results of this study support the notion that auditory short-term memory, like visual short-term memory, can be explained in terms of object formation. In particular, short-term memory performance is affected by stream formation and the perceptual costs involved in switching attention between multiple streams. Finally, effects of audiovisual integration were studied in a psychophysical experiment using complex speech-like stimuli (zebra finch songs). Results show visual cues improve performance differently depending on whether target identification is limited by energetic masking or whether it is limited by object formation difficulties and uncertainty about when a target occurs. Together, these studies support the idea that everyday communication depends on an interplay of many mechanisms including attention, memory, and multisensory integration, each of which is influenced by perceptual organization.
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Achtman, Rebecca L. "Investigation of shape processing using psychophysics and fMRI." Thesis, McGill University, 2003. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=82811.
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In the early stages of visual processing (primary visual cortex) shapes are sampled by discrete, localized, visual filters. The integration of the outputs of these local filters allows us to detect global shape information. Although this integration process is critical for visual processing beyond the primary visual cortex, it remains poorly understood. This thesis investigates what limits the performance of the mechanisms used to detect global structure. In particular, we asked four questions: (1) What information is important for detecting global form? (2) How well can we detect shape defined by changes in contrast? (3) Do the spatial properties of detectors that process global shape change across the visual field? (4) What cortical areas are involved in global shape processing?We used psychophysical methods and functional magnetic resonance imaging (fMRI) to study the integration of local filters for global shape processing in normal adult observers. All our stimuli were spatially bandpass and contained global circular structure.
Overall, our findings suggest that the visual system combines the outputs of local detectors both across the visual field and over different stimulus attributes (e.g. contrast, spatial frequency, spatial position, polarity, contrast-defined information). Our excellent sensitivity to these globally structured patterns suggests the involvement of higher-order mechanisms optimized for global processing. However, these higher-order mechanisms are not localized in an individual retinotopic area nor is there a systematic hierarchical increase in activity throughout the ventral processing pathway in response to globally structured stimuli. In conclusion, significant processing of shapes occurs at both the local and the global level.
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Tsakiris, Emmanouil. "Agency and the sense of body-ownership : psychophysical and neuroscientific investigations." Thesis, University College London (University of London), 2006. http://discovery.ucl.ac.uk/1446264/.
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Almost every human activity involves voluntary bodily movements. As agents, we act upon the world with our body, and we experience ourselves, and the world through the same body. This fact implies that the sense of self is crucially dependent on motor and sensory signals. These signals are related to the phenomenological experience of agency and body-ownership. Agency is the sense of oneself as being the source of the action, the sense that actions are one's own. Body-ownership is the feeling that the body I inhabit is mine and always with me. The sense of ownership is present not only during voluntary actions, but also during passive movement and at rest. In contrast, only voluntary actions should produce a sense of agency. Thus, agency seems to be closely linked to the generation of efferent motor signals, and ownership to the perception of afferent sensory signals. This distinction suggests that agency and ownership should have different effects on awareness of the body. The aim of the present thesis was to investigate how efferent and afferent signals interact to generate the sense of agency and the sense of ownership. In particular, the experiments focused on four main varieties of bodily experience: time-perception, sensory-motor perception, self-recognition, and self-attribution. Overall, the results showed a consistent contribution of voluntary action to a number of different measures related to the bodily self. In particular, efference underlies the sense of agency and at the same time functions as a unifying element that structures a coherent representation of the body. At the same time, the sense of body-ownership results as an interaction between bottom-up and top-down influences: sensory inputs related to the body are integrated against a set of body-scheme representations that guarantee the functional and phenomenological coherence of bodily experience. It is suggested that the unity of bodily self-consciousness comes from action, and not from sensation.
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Brusa, Adriana. "Long-term recovery following optic neuritis : evidence from serial electrophysiological and psychophysical investigations." Thesis, University College London (University of London), 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.311933.
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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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Whitlow, Laura. "An investigation of the link between cortical inhibition, neural oscillations and psychophysics in schizophrenia." Thesis, Cardiff University, 2016. http://orca.cf.ac.uk/88927/.
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Schizophrenia is a highly complex psychiatric disorder with a lifetime risk of approximately 0.4-0.7%. Alterations in the major inhibitory neurotransmitter GABA have been identified in the brains of those with schizophrenia. Studies examining the nature of these differences have given variable results depending on the type of patient group, medication and the brain region where in vivo MRS GABA was measured. Chapter 5 of this thesis utilises the noninvasive imaging tool magnetic resonance spectroscopy (MRS) to investigate differences in GABA levels in two distinct areas of the brain of those with schizophrenia, whilst adjusting for important potential confounds such as antipsychotic medication dosage. GABA is also of interest due to its link with synchronised oscillatory activity, primarily gamma activity that is implicated in connectivity between different brain regions as well as cognitive functioning, thus demonstrating its potential relevance to schizophrenia research. Chapter 6 investigates differences in gamma activity between those with schizophrenia and controls induced by a static stimulus and a moving radial stimulus, both known to induce strong visual gamma responses, using magnetoencephalography (MEG) imaging methods. Because GABA and gamma measures are robust for visual cortex measures, we used visual psychophysics tasks thought to be dependent on inhibitory processes - orientation discrimination and the tilt illusion, to see if there is a behavioural deficit in schizophrenia and if this also relates to changes in GABA and gamma measures. Chapters 3 and 4 set out to validate the psychophysics and to establish whether they were appropriate paradigms for the patient group for which they were intended. Chapter 7 brings together the imaging and psychophysics to see if a relationship exists between them in both the patient and control groups.
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Liu, Yue (Rebecca). "Investigating influence of streetscape elements on individual preference." Kansas State University, 2015. http://hdl.handle.net/2097/19702.
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Master of Landscape ArchitectureLandscape Architecture/Regional and Community Planning
Brent Chamberlain
Streets and sidewalks are important public places for a wide variety of activities, such as social interaction and physical activities. Public spaces can provide numerous benefits, such as physical, psychological, social, spiritual, and aesthetic wellbeing; in order to maximize these benefits effective planning and design is critical. However, there is a need to increase empirical data which can support good planning for these public spaces. The purpose of this research study is to better understand how different elements of streetscape design influence a person’s preferences for the design of the space. A streetscape consists of a variety of different infrastructure and natural forms, which are combined together to create a space centered on the movement of people. A survey was conducted with the aims to better understand how key design elements may influence users’ preferences with regard to safety and attractiveness. The project study site is Moro Street in Aggieville Business District in Manhattan, KS. The study and survey were developed using the psychophysical approach, which employed a quantitative methods to analyze the perceptions of Aggieville patrons. The research methods consists of four main parts: variable selection, streetscape design, public survey, and data analysis. An ANOVA was conducted that revealed statistically significant effects related to the preference for streetscape design in terms of safety and attractiveness, as well as a combined average evaluation. Evidence shows that the on street parking (Parking) and green infrastructure (Green Infrastructure) are statistically significant (p < .05), whereas seating and biking had no statistically significant effect on the evaluation of attractiveness. Also, the on street parking (Parking), green infrastructure (Green Infrastructure) and bike lane (biking)are statistically significant (p < .05), whereas seating had no statistically significant effect on the evaluation of safety. Overall, on street parking (Parking) and green infrastructure (Green Infrastructure) are statistically significant (p < .05), whereas seating and biking had no statistically significant effect on the evaluation of both safety and attractiveness. These results support previous work from environmental psychologists, and provide additional empirical evidence to support effective street design.
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Davidson, Kelly Patricia. "On unifying the laws of sensation : an empirical investigation of predictions arising from Norwich's theory of perception." Thesis, University of British Columbia, 1990. http://hdl.handle.net/2429/29594.
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The present thesis constitutes an empirical investigation of the prediction of Norwich's Entropy Theory of Perception that the positive exponent of the magnitude estimation power function and the negative exponents of equations relating the Weber fraction and simple reaction time to stimulus intensity should, since they can all be derived from the theory's Fundamental Equation, be numerically the same.
A pilot study consisting of magnitude estimation and reaction time experiments (using pure tone auditory stimuli of varying intensities at five frequencies), and a "main" study comprised of magnitude estimation, reaction time, and Weber fraction experiments are described.
The results, while offering possible confirmation of the prediction, remain somewhat tentative, owing to the persistently problematic technique of curve fitting upon which determination of the reaction time and Weber fraction exponents rests.
The theory, in leading one to even attempt to compare such previously unrelated measures as magnitude estimation and reaction time with Weber fractions, has yielded, theoretical issues aside, some worthwhile empirical results: I have obtained measures on three different psychophysical tasks from the same subjects over (effectively) the same stimulus range for each of those subjects; and, moreover have, I believe for the first time, explicitly noted that the Weber fraction displays the same decrease in exponent with increasing frequency, followed by an upturn at the highest frequencies, that characterizes both the equal loudness curves and the reaction time curves a la Chocholle. Suggestions are made regarding supplementary curve fitting methods by which to analyze these data, as well as for future research in the psychophysiological realm which, in addition to expanding the scope of the prediction that is being tested, may provide some much needed insight into the numerical values of the multiplicative and additive constants that occur in the equations under consideration in this thesis.Arts, Faculty of
Psychology, Department of
Graduate
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Acerbi, Luigi. "Complex internal representations in sensorimotor decision making : a Bayesian investigation." Thesis, University of Edinburgh, 2015. http://hdl.handle.net/1842/16233.
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The past twenty years have seen a successful formalization of the idea that perception is a form of probabilistic inference. Bayesian Decision Theory (BDT) provides a neat mathematical framework for describing how an ideal observer and actor should interpret incoming sensory stimuli and act in the face of uncertainty. The predictions of BDT, however, crucially depend on the observer’s internal models, represented in the Bayesian framework by priors, likelihoods, and the loss function. Arguably, only in the simplest scenarios (e.g., with a few Gaussian variables) we can expect a real observer’s internal representations to perfectly match the true statistics of the task at hand, and to conform to exact Bayesian computations, but how humans systematically deviate from BDT in more complex cases is yet to be understood. In this thesis we theoretically and experimentally investigate how people represent and perform probabilistic inference with complex (beyond Gaussian) one-dimensional distributions of stimuli in the context of sensorimotor decision making. The goal is to reconstruct the observers’ internal representations and details of their decision-making process from the behavioural data – by employing Bayesian inference to uncover properties of a system, the ideal observer, that is believed to perform Bayesian inference itself. This “inverse problem” is not unique: in principle, distinct Bayesian observer models can produce very similar behaviours. We circumvented this issue by means of experimental constraints and independent validation of the results. To understand how people represent complex distributions of stimuli in the specific domain of time perception, we conducted a series of psychophysical experiments where participants were asked to reproduce the time interval between a mouse click and a flash, drawn from a session-dependent distribution of intervals. We found that participants could learn smooth approximations of the non-Gaussian experimental distributions, but seemed to have trouble with learning some complex statistical features such as bimodality. To investigate whether this difficulty arose from learning complex distributions or computing with them, we conducted a target estimation experiment in which “priors” where explicitly displayed on screen and therefore did not need to be learnt. Lack of difference in performance between the Gaussian and bimodal conditions in this task suggests that acquiring a bimodal prior, rather than computing with it, is the major difficulty. Model comparison on a large number of Bayesian observer models, representing different assumptions about the noise sources and details of the decision process, revealed a further source of variability in decision making that was modelled as a “stochastic posterior”. Finally, prompted by a secondary finding of the previous experiment, we tested the effect of decision uncertainty on the capacity of the participants to correct for added perturbations in the visual feedback in a centre of mass estimation task. Participants almost completely compensated for the injected error in low uncertainty trials, but only partially so in the high uncertainty ones, even when allowed sufficient time to adjust their response. Surprisingly, though, their overall performance was not significantly affected. This finding is consistent with the behaviour of a Bayesian observer with an additional term in the loss function that represents “effort” – a component of optimal control usually thought to be negligible in sensorimotor estimation tasks. Together, these studies provide new insight into the capacity and limitations people have in learning and performing probabilistic inference with distributions beyond Gaussian. This work also introduces several tools and techniques that can help in the systematic exploration of suboptimal behaviour. Developing a language to describe suboptimality, mismatching representations and approximate inference, as opposed to optimality and exact inference, is a fundamental step to link behavioural studies to actual neural computations.
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Dugué, Laura. "Attentional and perceptual cycles : investigations using psychophysics, electroencephalography and transcranial magnetic stimulations : (cycles attentionnels et perceptuels)." Toulouse 3, 2013. http://thesesups.ups-tlse.fr/2184/.
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Analysons-nous le monde de façon continue ou bien selon une séquence d'évènements, un peu comme des instantanés pris par une caméra vidéo ? C'est la question qui a motivé ma thèse dans un premier temps. De précédentes expériences ont démontré que l'information visuelle était échantillonnée de façon périodique par l'attention, et que ce traitement était supporté par des oscillations de l'activité EEG. Dans le 1er papier, en utilisant la TMS, nous avons pu établir pour la première fois une relation causale entre la phase des oscillations spontanées, l'excitabilité cérébrale et la perception visuelle. Dans une autre série d'expériences, nous nous sommes demandé quel était le comportement spatio-temporel de l'attention au cours de tâches de recherche visuelle. A l'aide de diverses expériences (papiers 2 à 4) et de différentes techniques (TMS, EEG, psychophysique), nous avons pu établir des arguments convaincants en faveur d'un échantillonnage périodique de l'information visuelle par l'attention. De plus, dans le 5ème papier, nous avons pu clarifier une question hautement débattue concernant les tâches de recherche visuelle en éliminant la possibilité d'un traitement en parallèle de l'intégralité des stimuli présents à l'écran, suggérant un traitement séquentiel des différents stimuli au cours de la recherche. Ce travail de thèse a permis d'apporter des arguments forts en faveur d'un traitement périodique, voire séquentiel, de l'information visuelle par l'attentionDo we experience the world continuously or as a discrete sequence of events, like samples of a video camera? This is the first question motivating my PhD work. Previous experiments have shown that visual information may be sampled periodically by attention, this processing being supported by oscillations in the EEG brain activity. In paper 1, using TMS, we were able to establish for the first time a causal relation between the phase of ongoing oscillations, brain excitation and visual perception. In another series of experiments, we explored the spatio-temporal behaviour of attention during visual search tasks. Using various experiments (papers 2 to 4) and various techniques (TMS, EEG, psychophysics), we brought convincing and converging evidence in favour of a periodic sampling of visual information by attention. Moreover, in paper 5, we were able to clarify an age-old debate concerning visual search tasks by ruling out the possibility that attention is distributed in parallel over all stimuli in the search array, suggesting a sequential processing of the different stimuli during the search. Overall, this PhD work gives strong arguments in favour of a periodic, and perhaps sequential, processing of visual information by attention
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McFall, Kristen Elaine. "A psychophysical investigation of grip types with specific application to job rotation." Thesis, 2008. http://hdl.handle.net/10012/3475.
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Job rotation is recommended to prevent musculoskeletal disorders (MSD). The premise is by involving different tissues a “working rest” for other tissues is created. The possible health benefits from this relief have not been investigated with regards to different grips in hand intensive jobs. The purpose of this study is to investigate hand intensive tasks and determine whether rotating between the power grip and lateral pinch grip can provide a benefit. A psychophysical load adjustment protocol was used.
To investigate the effect of rotation, three different trials were collected. These included: power grip only, lateral pinch only, and alternating the two grips. Each trial was 60 minutes in duration, with a 12second cycle time, and 25% duty cycle.
Fourteen subjects were recruited and pre-screened for any upper extremity disorders. Subjects were instructed to “work as hard as you can without straining your hand, wrist or forearm”; by adjusting their resistance settings to achieve a maximum acceptable force (MAF). Grip forces were exerted on an adjustable system using a hand grip dynamometer. Ratings of perceived discomfort were reported every 10minutes. Electromyography (EMG) was collected on eight forearm muscles during the combination trial.
The demand for both lateral pinch and power grip tasks were at self selected levels and no fatigue was reported within MAF, EMG recordings, and discomfort reports. The rotation between lateral pinch and power grip had no apparent effect on MAF. However, EMG data hinted that there was a rotation of activation between first dorsal interossei and the forearm flexors (not statistically significant). Less discomfort was reported within the combination trial than the single grip (not significant).
The study found no measurable difference in MAF when rotating between the power grip and lateral pinch. Considering there was no increase in demand, there is potential benefit to rotation, with trends to rotating activation between muscles, less discomfort being reported, and a general preference for the rotation. Given the high rates of MSD, and rotation being an effective tool to lower exposure, further investigations are required to understand relationships between similar muscles groups within hand intensive work environments.
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Cobo-Lewis, Alan Blake. "A psychophysical investigation of mechanisms selective for the spatial frequency of disparity modulation in random-dot stereograms." 1992. http://catalog.hathitrust.org/api/volumes/oclc/28687480.html.
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Timora, Justin Ronald. "Extending the temporal principle of multisensory integration: a psychophysical and EEG investigation of cross-modal acoustic and vibrotactile amplitude modulation." Thesis, 2019. http://hdl.handle.net/1959.13/1407902.
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Research Doctorate - Doctor of Philosophy (PhD)The major aim of the current thesis was to examine whether the temporal principle of multisensory integration could be extended to include the cross-modal temporal congruence of other stimulus features. According to the temporal principle, cross-modal synchrony between the onsets of multisensory stimuli is fundamental to the binding of multisensory information, or multisensory integration. The examination of other temporal features in multisensory contexts remains limited. Amplitude modulation (AM) has an analogous influence on auditory and vibrotactile sensory processing and perception. This cross-modal dependence of the auditory and tactile modalities on temporal processing potentially facilitates multisensory integration. However, the role of this temporal feature in auditory and vibrotactile multisensory integration remains unexplored. Psychophysical studies show that both auditory and vibrotactile sensitivity varies as a function of AM rate. Electroencephalography (EEG) research shows that the steady-state response (SSR), a sensitive measure of entrained oscillatory mechanisms, is also sensitive to AM rate. It has been proposed that the SSR reflects oscillatory activity with a functional role in the perceptual analysis of the temporal features of sensory stimulation. Subsequently, the SSR may be a potentially important EEG measure for multisensory integration, as recent theories propose that entrained oscillatory activity provides a flexible and dynamic mechanism for multisensory integration. It currently remains unknown as to whether the entrained oscillatory activity underlying the SSR also plays a vital role in auditory and tactile multisensory integration. Across four separate studies, the current thesis investigates how the cross-modal temporal congruence between auditory and vibrotactile stimuli influences perceptual sensitivity, SSR activity and the potential relationship between them. Taken together, findings from the current thesis propose that the cross-modal temporal congruence of temporal features, beyond stimulus onset synchrony, can dramatically influence perceptual sensitivity and the SSR. However, little evidence was found to suggest that the temporal principle extends to acoustic and vibrotactile amplitude modulation congruence.
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Fischer, Steven. "A biomechanical investigation into the link between simulated job static strength and psychophysical strength: Do they share a “weakest link” relationship?" Thesis, 2011. http://hdl.handle.net/10012/5717.
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Maximum voluntary forces and psychophysically acceptable forces are often used to set force guidelines for exertions as a means to protect against overexertion injuries in the workplace. The focus of this dissertation was the exploration of the roles of whole body balance, shoe-floor friction and joint strength in limiting the capacity of a person to produce maximum voluntary hand forces and psychophysically acceptable hand forces. The underlying goal was to advance knowledge regarding how physical exertion capacity is biomechanically governed, then to use this information to develop models to predict capability based on these governing principles. The hypothesis underscoring this work was that maximum voluntary hand force capability is governed by whole body balance, shoe-floor friction and joint strength; and consequently, psychophysically acceptable forces would be chosen proportionally to this maximum voluntary force capability, where the magnitude of the proportionality was dependent on the limiting factor, or ‘weakest link’.
To investigate this hypothesis, both experimental and mathematical modeling paradigms were used. Initially, an experimental study was used to investigate how biomechanical factors governed maximum hand force capability across a range of exertions. It revealed that each governing factor differentially limited maximum force capability. Moreover, this study identified how foot placement, handle height, distance from the handle, friction, and body posture all influence the underlying biomechanical weakest link, and ultimately force producing capability.
Data gathered in the experimental study was next used to evaluate a mathematical model that was developed to predict maximum force capability, given information on posture and direction of force application. In addition, the model also predicted population variability in maximum capacity based on the inclusion of a novel approach to probabilistically represent population variability. The evaluation demonstrated that the model underestimated maximum hand force capability compared to measured hand forces by approximately 18, 26, and 41% during medial, pulling and downward exertions respectively. However, it appeared that the ‘weakest link’ principle for predicting maximum force capacity was plausible, as evidenced by significant rank ordered correlations between the measured and predicted hand forces.
Further research investigated if psychophysically acceptable forces were selected as a proportion of task specific maximum voluntary force capability, where the proportionality was related to the biomechanical weakest link. Using an experimental design, psychophysically acceptable forces and corresponding maximum forces were measured. Participants chose psychophysically acceptable forces that were 4/5ths of their task specific maximum voluntary force capability when capability was limited by balance. Additionally, they choose psychophysically acceptable forces that were 2/3rds of their maximum voluntary force capability when capability was limited by joint strength. The identification and confirmation of a weakest link proportionality principle represents an important contribution to the field of occupational biomechanics.
The weakest link proportionality principle was integrated into the model to allow prediction of: maximum voluntary hand force capability, the limiting factor, and psychophysically acceptable hand force capability. The updated model underestimated empirically measured psychophysically acceptable forces by 24% and 43% during downward and pulling exertions respectively. However, the original model underestimated the maximum hand force capacity by 23% and 34% during the same exertions, without the proportional relationships. This underestimation may be a result of the underlying assumption that joint strength is independent, resulting in an underestimation of maximum joint strength capacity and a corresponding underestimation of maximum hand force capacity. The underestimation may also be due to differences in strength capacities between the participants tested during this thesis compared to those tested in past research used to determine the maximum strength indices reported in the literature.
This body of work supported the hypothesis that psychophysically acceptable forces are selected as a proportion of the maximum voluntary hand force, where the proportionality depends on the underlying biomechanical weakest link. The model is a promising first step towards predicting maximum and psychophysically acceptable occupational force threshold limits.
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Ragert, Patrick [Verfasser]. "Investigation of the relation between perceptual changes and cortical reorganization within the somatosensory cortex through passive stimulation protocols and modified use : a psychophysical and neurophysiological study in humans / Patrick Ragert." 2004. http://d-nb.info/974108294/34.
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Basuthkar, Sundar Rao Subam. "Psychophysical and Clinical Investigations of Ocular Discomfort." Thesis, 2012. http://hdl.handle.net/10012/7030.
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Purpose
To investigate ocular surface sensations, specifically ocular discomfort using psychophysical and clinical techniques. The measurement of discomfort on the ocular surface has been limited to the use of traditional rating scales until recently. This thesis focuses on the scaling of discomfort using a psychophysical approach and also investigates the less explored area of the influence of blur on ocular discomfort.
The specific aims of each chapter are:
Chapter 2: To evaluate the difference thresholds of the central cornea in lens and non-lens wearers.
Chapter 3: To devise a novel scale for ocular discomfort, relating subjective estimation of discomfort arising from contact lens wear to discomfort produced by the pneumatic stimuli delivered by a modified Belmonte esthesiometer.
Chapter 4: To evaluate the influence of blur on ocular comfort while systematically manipulating vision using habitual refractive correction, induced spatial and optical blur, and under the absence of visual structure.
Chapter 5: To examine if subjects rate discomfort and intensity of suprathreshold pneumatic stimuli differently when viewing clear and defocused targets and to examine the suprathreshold scaling of stimuli under the same visual conditions.
Methods
Chapter 2: The mechanical sensitivity of the central cornea was determined in 12 lens wearers and 12 non-lens wearers using a modified Belmonte pneumatic esthesiometer. The mechanical threshold of the central cornea was first estimated using the method of limits. Then, a series of systematically increasing stimuli were presented, with the first stimuli being 25% less than the threshold. The subjects were asked to compare the intensity of each stimulus with the preceding one and report if any difference in intensity was detectable. The intensities at which the subjects perceived an increased intensity from the previous was recorded. The difference threshold (DL) was the differences between the stimulus intensities at which an increase was perceived and five DLs were measured for each subject. Weber’s constants that relate the size of the difference thresholds to the stimulus intensity were derived for each DL level and repeated measures ANOVA was used to compare the Weber’s constants in the lens and non-lens wearing groups.
Chapter 3: Twenty seven participants were enrolled for this magnitude matching study. Soft (HEMA) contact lenses of eight different lens designs varying in base curve and diameter were fit on all participants. The study was conducted on two separate days with four lenses randomly assigned on each day. The assigned soft contact lens was placed on the chosen eye and the sensations were measured using a numerical rating scale. Following this, the subjects were asked to regulate the intensity of the pneumatic stimulus using the control dial in order to match the discomfort from the stimulus to the discomfort from contact lens wear. At the completion of magnitude matching, ratings of sensations were again recorded. Pearson product moment correlation was used to correlate the objective esthesiometer matches to the subjective ratings of discomfort reported by each participant. The method of least log squares was used to derive the power exponents as defined by Stevens’ power law and analyze the psychophysical functions. Repeated measures ANOVA was used to investigate the effect of lens sequence and session on ocular discomfort with contact lens wear. The impact of lens type and time on discomfort was studied using linear mixed modeling.
Chapter 4: Twenty emmetropic subjects rated ocular comfort, vision and sensation attributes (burning, itching and warmth) under conditions of normal vision, spatial blur and dioptric defocus, each session lasting for five minutes. Subjects viewed digital targets projected from a distance of 3m, and ocular surface sensations, vision were rated using magnitude estimation. Dioptric defocus was produced using +6.00DS contact lenses and equivalent spatial blur was created by spatially blurring the targets. Clear target images were used during dioptric defocus and blurred images during spatial blur session. Comfort was also rated under the absence of visual structure in fifteen of the participants using a ganzfeld and black occluders. Repeated measures ANOVA was used to compare vision and comfort ratings between the different experimental conditions.
Chapter 5: Twenty one participants were enrolled. Ocular discomfort was produced by delivering mechanical stimuli from a pneumatic esthesiometer, and participants were asked to rate the intensity of stimulus and the discomfort induced by it under clear and defocused visual conditions. Esthesiometry was performed on one eye while the fellow eye viewed either a clear or blurred 6/60 fixation target through a trial lens. For the clear visual condition, the trial lens contained +0.25DS over their distance refractive correction and for the defocused condition, an additional +4.00DS was used. Mechanical thresholds from the central cornea were estimated using ascending methods of limits and then stimuli that were 25%, 50%, 75% and 100 % above threshold were presented in random order. Participants rated intensity and discomfort of each stimulus using a 0-100 numerical scale where 0 indicated no sensation and 100 indicated highest imaginable intensity/discomfort. There were 3 sessions with clear visual conditions and 3 sessions with defocus, in random order.
Results
Chapter 2: The functions relating Weber’s constants to stimulus intensities were slightly different in lens and non-lens wearing groups, although the absolute thresholds were similar. Repeated measures ANOVA revealed a significant main effect of DL level on Weber’s constant (p<0.001), with the Weber’s fraction at the first DL being higher than the following DLs. A significant main effect of the group type was also observed, with the lens wearers showing higher Weber’s constants than the non-lens wearers (p=0.02) However, there was no interaction between DL level and lens wearing group on Weber’s constants (p=0.38).
Chapter 3: The average and individual psychophysical functions appeared to follow Stevens’ power function, with mechanical and chemical stimuli giving rise to different power exponents. Examination of the individual transducer functions revealed that only about half of the subjects were able to match the contact lens sensations to the pneumatic stimulus discomfort, with both mechanical and chemical stimulation. The lens types did not have any impact (p=0.65) on the session or sequence in which the lens was presented, although an effect of session and sequence on discomfort was observed. The average discomfort ratings produced by the different lens types were similar. There appeared to be significant effects of time (p<0.001) on the reporting of discomfort with lens wear, with the discomfort upon lens insertion rated to be higher than after lenses settling.
Chapter 4: Ratings of vision under spatial blur and dioptric defocus were significantly different (p<0.001) from normal vision condition. Vision with dioptric defocus was rated worse (p<0.001) than spatial blur. Significant differences in comfort were observed between normal vision and blur, including spatial blur (p=0.02) and dioptric defocus (p=0.001). However, there was no significant difference (p=0.99) in comfort between spatial blur and dioptric defocus. Comfort remained unchanged between normal vision, occluders and ganzfeld although vision was absent in the later two conditions.
Chapter 5: There was no significant difference in mechanical thresholds under clear and defocused conditions with a paired t-test (p=0.66) and similar results were obtained with repeated measures ANOVA, with no significant difference in discomfort (p=0.10) and intensity (p=0.075) ratings between the two visual conditions. However, paired t-test between the derived exponents under clear and defocused conditions showed significant differences for discomfort (p=0.05) and no significant difference for the ratings of intensity (p=0.22). Comparison of exponents between discomfort and intensity showed a significant difference in both clear (p=0.02) and defocus conditions (p<0.001).
Conclusions:
Chapter 2: The differential sensitivity of the ocular surface can be successfully measured with a pneumatic esthesiometer and it appears that Weber’s law holds true for corneal nociceptive sensory processing. There are subtle differences in mechanical difference thresholds between lens and non-lens wearers suggesting the possibility of different neural activity levels in the two groups.
Chapter 3: Subjective ratings of discomfort can be scaled by corneal esthesiometry in a selective group of people. In the subset of subjects with poorer correlations, perhaps the pneumatic mechanical stimulus was too localized and specific to match the complex sensations experienced while wearing contact lenses. However, there is also a group of subjects who are poor at making judgments about ocular comfort. Hence, the use of special sensory panels should be considered when ocular comfort is the primary outcome.
Chapter 4: There does seem to be an association between clarity of vision and ocular comfort, although the pathways for pain and vision are perhaps exclusive. Interactions between vision and
other senses have been reported, but a similar inter-sensory interaction between pain and vision is yet to be clearly demonstrated. The decreased comfort observed in this study might perhaps be due to nocebo or Hawthorne effects.
Chapter 5: Suprathreshold scaling of pneumatic stimuli can vary with the viewing conditions, with defocus associated with higher exponents than clear visual conditions. However, the ratings of comfort appear to be similar under both the conditions. If defocus does affect comfort, it is subtle and does not affect the sensory components, but tiny effects through the affective aspect of pain can contribute to the differences in power exponents. The differences in the perception of comfort do not appear to be attributable to the differences in threshold or sensory intensity.
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Chami, Abdullah. "An Investigation of the Velvet Hand Illusion Using Computational Mechanics and Psychophysics." Thesis, 2011. http://hdl.handle.net/2237/14821.
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Lin, Yong-Jun. "Human Duration Perception Mechanisms in the Subsecond Range: Psychophysics and Electroencephalography Investigations." Thesis, 2018. https://thesis.library.caltech.edu/11005/1/YongJunLin2017Thesis_v41_YJL_20180601.pdf.
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In a world full of fleeting events, how do humans perceive time intervals as short as half a second? Unlike primary senses, there are no time receptors. Is sub-second time perception reconstructed from memory traces in the primary senses, or based on the output of a modality-independent internal clock? In analogy to bugs in computer programs or mutations in genetics studies, I studied two types of subjective time warp illusions in order to understand how time perception normally works. One illusion that I examined is called oddball chronostasis, which is a duration distortion effect that happens to an unusual item. The other illusion is called debut chronostasis, which is a time warp effect that occurs to the first item among other identical ones.
Regarding oddball chronostasis, we solved a theoretical dispute over its underlying mechanisms and dissociated three causes. The necessary component is top-down attention to the target item. The other two components are contingent factors. This suggests that a pure sensory modality-dependent view of time perception mechanisms is less likely. Regarding debut chronostasis, we discovered auditory debut chronostasis and found that its illusion strength is about the same as the visual case. At first glance, this seems to suggest that time perception is independent of the primary sensory modalities. However, when visual and auditory events were compared against each other (inter-modal comparison), debut chronostasis disappeared. Therefore, modality-dependent mechanisms of time perception do exist. Further, we found a special factor that could counteract debut chronostasis and thus re-interpreted the main cause of debut chronostasis as internal duration template uncertainty. By examining both intra- and inter-modal comparisons, this uncertainty effect turned out to be a modality-independent effect. Therefore, modality-independent mechanisms of time perception also exist.
In conclusion, this dissertation work contributed to novel theoretical understanding of two types of time perception illusions. Unlike many simplified theories in the literature either holding a modality-dependent or independent view, our findings altogether indicate that time perception involves both intra- and supra-modal stages. Future experimental work could thus target on separating intra- and supra-modal time perception mechanisms.
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Lee, Yunjo. "Face representation across changes in viewpoint and image size : psychophysical investigations of neurologically intact people and prosopagnosic individuals /." 2008. 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:NR39024.
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Thesis (Ph.D.)--York University, 2008. Graduate Programme in Psychology.Typescript. Includes bibliographical references (leaves 228-251). Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: 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:NR39024
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Susilo, Bagus Tirta. "The representation of face identity in the human visual system : psychophysical investigations of face space and holistic processing." Phd thesis, 2010. http://hdl.handle.net/1885/150512.
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The topic of the present thesis is the representation of face identity within the human visual system, framed within the widely used theoretical ideas of face space and holistic processing. The thesis investigates several questions regarding the properties of face space and holistic processing in four psychophysical studies. The first study examines coding sensitivity of attribute values (e.g., eye heights) along a trajectory in face space. Using face aftereffects and pairwise discrimination tasks, the primary result was of an equally sensitive representation of attribute values that are relatively common (e.g., typical eye heights) and of those that are relatively rare (e.g., unusual eye heights). The second study explores the extent to which face aftereffects tap a face space that is specific to upright faces. The major result was that, while both upright and inverted face aftereffects derive from opponent (norm-based) rather than multichannel (exemplar-based) coding, their origin differs qualitatively in that approximately half of the upright aftereffect was face-specific, while the inverted face aftereffect was almost entirely shape-generic. The third study asks whether holistic processing can be modulated by recent experience with a particular face type, specifically own-age faces. Using the composite task, results showed that holistic processing is stronger in children than adults for child faces. The final study assesses whether face space and holistic processing can remain normal in a case of developmental prosopagnosia. Results from a series of aftereffect experiments and multiple composite tasks indicated that despite lifelong impairment of face recognition, face space and holistic processing mechanisms can develop in a normal manner. Together, the findings of this thesis have broad implications for several topics; these include general coding principles used throughout the visual system, issues concerning coding and representation in face space, and the relationship between face space and holistic processing.
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Olsen, Kirk N. "Perceptual bias and loudness change : an investigation of memory, masking, and psychophysiology." Thesis, 2011. http://handle.uws.edu.au:8081/1959.7/499833.
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Loudness is a fundamental aspect of human auditory perception that is closely associated with a sound's physical acoustic intensity. The dynamic quality of intensity change is an inherent acoustic feature in real-world listening domains such as speech and music. However, perception of loudness change in response to continuous intensity increases (up-ramps) and decreases (down-ramps) has received relatively little empirical investigation. Overestimation of loudness change in response to up-ramps is said to be linked to an adaptive survival response associated with looming (or approaching) motion in the environment. The hypothesised 'perceptual bias' to looming auditory motion suggests why perceptual overestimation of up-ramps may occur; however it does not offer a causal explanation. It is concluded that post-stimulus judgements of perceived loudness change are significantly affected by a cognitive recency response bias that, until now, has been an artefact of experimental procedure. Perceptual end-level differences caused by duration specific sensory adaptation at peripheral and/or central stages of auditory processing may explain differences in post-stimulus judgements of loudness change. Experiments that investigate human responses to acoustic intensity dynamics, encompassing topics from basic auditory psychophysics (e.g., sensory adaptation) to cognitive-emotional appraisal of increasingly complex stimulus events such as music and auditory warnings, are proposed for future research.
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Koucoulas, Dean. "Investigating Perception Under Dynamic Auditory Conditions in the Acoustic Parasitoid Fly Ormia ochracea." Thesis, 2013. http://hdl.handle.net/1807/42994.
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Behavioural phonotaxis (oriented movement in response to sound) is an effective means to quantify auditory perception in acoustically communicating insects. Previous phonotaxis studies on the acoustic parasitoid fly Ormia ochracea (Diptera: Tachinidae) have described stereotyped, reflex-like responses towards auditory stimuli modeled after their preferred cricket hosts, yet their ability to demonstrate plasticity of responses in the context of dynamically changing auditory cues has not previously been described. Using a behavioural sensitization protocol, I compared phonotaxis towards behaviourally irrelevant (non-attractive) test stimuli presented alone, and when preceded with the natural, response-evoking cricket song (attractive). Results demonstrate the cricket song as a sensitizing stimulus mediating phonotaxis towards otherwise non-attractive sounds, and differential walking patterns depending on temporal delay between song offset and test stimulus onset. My findings suggest an ecological purpose of sensitization, allowing flies to maintain orientation towards a cricket host amidst conditions of signal disruption in the environment.