Dissertations / Theses on the topic 'Binocular rivalry'

Binocular rivalry refers to the perceptual alternation that occurs while viewing incompatible images, in which one monocular image is dominant and the other is suppressed. Rivalry has been closely studied but the neural site at which it is initiated is still controversial. The central claim of this thesis is that primary visual cortex is responsible for its initiation. This claim is supported by evidence from four experimental studies. The first study (described in Chapter 4) introduces the methodology for measuring visual sensitivity during dominance and suppression and compares several methods to see which yields the greatest difference between these two sensitivities. Suppression depth was measured by comparing the discrimination thresholds to a brief test stimulus delivered during dominance and suppression phases. The deepest suppression was achieved after a learning period, with the test stimulus presented for 100 ms and with post-test masking. The second study (Chapter 5) compares two hypotheses for the mechanism of binocular rivalry. Under eye suppression, visibility decreases when the tested eye is being suppressed, regardless of the test stimulus’s features. Feature suppression, however, predicts that reduction of visibility is caused by suppression of a stimulus feature, no matter which eye is suppressed. Eye suppression claims that monocular channels in the visual system alternate between dominance and suppression, while Feature suppression assumes that the features of stimuli inhibit each other perceptually in the high-level cortex. The experiment used a test stimulus similar in features to one, but not the other, rivalry-inducing stimulus. Test sensitivity was found to be lowered when the test stimulus was presented to the eye whose rivalry-inducing stimulus was suppressed. Sensitivity was not lowered when the test stimulus was presented to the other eye, even when the test shared features with the suppressed stimulus. The conclusion is that feature suppression is weak or does not exist without eye suppression, and that rivalry therefore originates in the primary visual cortex. If binocular rivalry is initiated in the primary visual cortex, stimuli producing no coherent activity in that area should produce no rivalry. In the third study (Chapter 6) this idea was tested with rotating arrays of short-lifetime dots. The dots with the shortest lifetime produced an image with no rotation signal, and an infinite lifetime produced rigid rotation. Subjects could discriminate the rotation direction with high accuracy at all but the shortest lifetime. When the two eyes were presented with opposite directions of rotation, there was binocular rivalry only at the longest lifetimes. Stimuli with short lifetimes produce a coherent motion signal, since their direction can be discriminated, but do not produce rivalry. A simple interpretation of this observation is that binocular rivalry is initiated at a level in the visual hierarchy below that which supports the motion signal. The model supported by the results of previous chapters requires that binocular rivalry suppression be small in the primary visual cortex, and builds up as signals progress along the visual pathway. This model predicts that for judgements dependent on activity in high visual cortex: 1. Binocular rivalry suppression should be deep; 2. Responses should be contrast invariant. The fourth and last study (chapter 7) confirmed these predictions by measuring suppression depth in two ways. First, two similar forms were briefly presented to one eye: the difference in shapes required for their discrimination was substantially greater during suppression than during dominance. Second, the two forms were made sufficiently different in shape to allow easy discrimination at high contrast, and the contrast of these forms was lowered to find the discrimination threshold. The results in the second experiment showed that contrast sensitivity did not differ between the suppression and dominance states. This invariance in contrast sensitivity is interpreted in terms of steep contrast-response functions in cortex beyond the primary visual area. The work in this thesis supports the idea that binocular rivalry is a process distributed along the visual pathway. More importantly, the results provide several lines of evidence that binocular rivalry is initiated in primary visual cortex.

Binocular rivalry is the perceptual consequence of dichoptic input which is not congruent between both visual inputs. There is some evidence, both theoretical and empirical, that the perception of binocular rivalry is mediated by interactions between binocular neurones, rather than by interactions between monocular neurones. This evidence suggests also a model of perception which predicts binocular rivalry as a consequence of normal interactions between binocular neurones in a retinotopic array. This model accounts for rivalry without postulating any additional interconnections beyond those already thought to exist between binocular neurones simply assumes an orderly mapping of tuning characteristics across groups of cells, as is typically observed in visual cortex. On the basis of this model, and findings already reported, it was hypothesised that binocular rivalry reflects extrastriate rather than area V1 processing (no process so far attributed to area V1 has yet been reported to be affected by binocular rivalry). It was hypothesised also that area V2 was the most likely area in which such processing first arises. Area V2 has been associated with the perception of 'purely subjective contours'. It has been shown that some cells in area V2 are tuned for such contours, which are characterised by the absence of Fourier components at the orientation of the perceived contour, while no cells in area V1 have been found to be similarly sensitive (von der Heydt and Peterhans 1989). This characteristic of area V2 neurones enables purely subjective contours to be used to test the two hypotheses described above. Real contour tilt aftereffects, which are thought to arise in area V1, are not affected by rivalry during their induction. If purely subjective contour tilt aftereffects (Paradiso, Shimojo and Nakayama 1989) are subject to the same types of processing as their real contour counterparts, as suggested by the rationale and model of von der Heydt and Peterhans (1989), interactions between subjective contour tilt aftereffects and binocular rivalry should indicate the role, if any, of area V2 in rivalry. It was found that purely subjective contour tilt aftereffects (Experiment One) and tilt illusions (Experiment Four) exhibit angular functions like those observed for real contour tilt aftereffects and illusions. Just as for real contour effects, these functions can be described in terms of direct effects (Experiment Two) and indirect effects (Experiment Three), suggesting purely subjective contours are processed as if they were real contours. Unlike real contour direct effects, purely subjective contour direct and indirect effects are reduced in magnitude by periods of rivalry during their induction (Experiment Five). In keeping with their suggested extrastriate locus (eg. Wenderoth, van der Zwan and Williams 1993), the magnitude of a real contour indirect effect is also reduced by periods of rivalry occurring during its induction (Experiment Six). These results suggest that rivalry does arise first in area V2. If this is true then complete interocular transfer of the purely subjective aftereffect, induced with or without rivalry, should occur because area V2 is almost exclusively binocular. This proved not to be the case, however, suggesting the ocular dominance observed in most binocular cells has to be taken into account in any explanation of rivalry (Experiment Seven). This was tested using real contours and found to be the case. These last results suggested also that rivalrous interactions occur between groups of binocular neurones only in extrastriate cortex (Experiment Eight). This hypothesis was tested by examining the effect of binocular rivalry on the duration of the plaid motion aftereffect, which is thought to arise no earlier than area MT, a visual cortical area which is also thought to be almost exclusively binocular. It was found that rivalry did reduce the duration of plaid motion aftereffects but not linear motion aftereffects, and that the impact of rivalry might be linked to plaid sensitive cells in area MT, although this last conclusion is tenuous (Experiments Nine and Ten). Finally, it was shown also that the magnitude of the reduction in duration of the aftereffect was proportional to the predominance of the plaid stimulus during rivalry, a finding which supports the mechanism of rivalry suggested by the binocular model. The results together suggest that binocular rivalry does arise through binocular interactions, but that such interactions cannot be attributed to a single cortical area. All groups of binocular neurones may be subject to the processes that ultimately give rise to the perception of rivalry, a conclusion which does not invalidate the binocular model of rivalry. This has some consequences for binocular vision, particularly stereopsis, which might occur qualitatively during binocular rivalry.

When the two eyes are presented with dissimilar images, the brain has to select one percept for awareness while suppressing the other. Interocular suppression describes the loss of Visibility of one image in favour of its competitor, and can be seen as a mechanism for understanding how, why, and Where percept selection occurs within the Visual system. This thesis addresses how and where interocular suppression takes place. By comparing the time courses of interocular With intraocular suppression, that is, Visibility loss due to conflicting images presented to only one eye, the major goal of the thesis is to show that interocular suppression occurs in two stages along the visual pathway. Four lines of experimental evidence are presented. When Viewing a monocular conditioning stimulus, the abrupt onset of a brief stimulus to the opposite eye results in a switch in perception to the new stimulus. This phenomenon is known as flash suppression. The first study (Chapter 4) investigated flash suppression under monocular and dichoptic viewing conditions to provide the intraocular and interocular time courses, respectively. This was carried out by probing Visual sensitivity to a test stimulus before, during, and after the appearance of the flash stimulus. The time course measured was the variation of threshold across time. The intraocular time course had a single elevation, a transient peak occurring Close to the time the flash stimulus was introduced. The interocular time course, on the other hand, had two elevations: the first peak was similar to that of the intraocular time course, and the second was a sustained peak starting about 100 ms later. The second study (Chapter 5) used visual masking as a technique for eliciting intraocular and interocular suppression, through monocular and dichoptic masking, respectively. In the dichoptic masking condition, one eye was presented with a masking stimulus for 100 ms. After a varying inter-stimulus interval, a brief test stimulus was presented to the other eye. The contrast threshold of the test stimulus was measured for each inter-stimulus interval. For monocular masking, both masking and test stimuli were presented to the same eye. The results showed a two-staged time course for interocular suppression, which was not apparent in intraocular suppression. Additionally, interocular suppression was more prolonged than intraocular suppression. The third study (Chapter 6) measured suppression using a different approach to the first and second studies. The experiment investigated crossorientation interactions using a stream of rapidly-changing grating orientations displayed to one eye and an independent stream to the other eye. One orientation was nominated as the target, and participants pressed a key when they saw the target. Using a reverse correlation technique, probability densities of two orientations were found. The first, 61, preceded the key-press by the reaction time, and the second, 02, preceded 61 by several hundreds of milliseconds. Analysis of the data examined the cross-orientation interactions between 6] and 92 for grating streams presented to the same eye (intraocular effect), and to different eyes (interocular effect). Despite the differences in experimentation methods between this and the masking study, the prolonged interocular suppression time course was once again apparent in the cross-orientation experiments.

Binocular rivalry is an interesting phenomenon where perception oscillates between different images presented to the two eyes. This thesis is primarily concerned with modelling travelling waves of visual perception during transitions between these perceptual states. In order to model this effect in such a way that we retain as much analytical insight into the mechanisms as possible we employed neural field theory. That is, rather than modelling individual neurons in a neural network we treat the cortical surface as a continuous medium and establish integro-differential equations for the activity of a neural population. Our basic model which has been used by many previous authors both within and outside of neural field theory is to consider a one dimensional network of neurons for each eye. It is assumed that each network responds maximally to a particular feature of the underlying image, such as orientation. Recurrent connections within each network are taken to be excitatory and connections between the networks are taken to be inhibitory. In order for such a topology to exhibit the oscillations found in binocular rivalry there needs to be some form of slow adaptation which weakens the cross-connections under continued firing. By first considering a deterministic version of this model, we will show that, in fact, this slow adaptation also serves as a necessary "symmetry breaking" mechanism. Using this knowledge to make some mild assumptions we are then able to derive an expression for the shape of a travelling wave and its wave speed. We then go on to show that these predictions of our model are consistent not only with numerical simulations but also experimental evidence. It will turn out that it is not acceptable to completely ignore noise as it is a fundamental part of the underlying biology. Since methods for analyzing stochastic neural fields did not exist before our work, we first adapt methods originally intended for reaction-diffusion PDE systems to a stochastic version of a simple neural field equation. By regarding the motion of a stochastic travelling wave as being made up of two distinct components, firstly, the drift-diffusion of its overall position, secondly, fast fluctuations in its shape around some average front shape, we are able to derive a stochastic differential equation for the front position with respect to time. It is found that the front position undergoes a drift-diffusion process with constant coefficients. We then go on to show that our analysis agrees with numerical simulation. The original problem of stochastic binocular rivalry is then re-visited with this new toolkit and we are able to predict that the first passage time of a perceptual wave hitting a fixed barrier should be an inverse Gaussian distribution, a result which could potentially be experimentally tested. We also consider the implications of our stochastic work on different types of neural field equation to those used for modelling binocular rivalry. In particular, for neural fields which support pulled fronts propagating into an unstable state, the stochastic version of such an equation has wave fronts which undergo subdiffusive motion as opposed to the standard diffusion in the binocular rivalry case.

Binocular rivalry can occur when incompatible stimuli are presented separately to the eyes. Since the invention of the stereoscope by Wheatstone in 1838, binocular rivalry has been intensively investigated with visual stimuli, which are differentiated from the background by variations in luminance, so-called luminance-modulated stimuli. However, it is also possible to perceive stimuli for which luminance of the target does not differ from that of the background but instead varies in contrast: so-called contrast-modulated (CM) stimuli. The main aim of this thesis is to investigate CM and noisy luminance-modulated (LM) stimuli under binocular rivalry conditions as the gained knowledge would enhance our understanding of both CM processing, as well as binocular rivalry. Perceptual change rates, proportions of exclusive visibility, mixed percepts (i.e. piecemeal and superimposition), as well as changes of these proportions across time and distributions of perceptual phases were calculated and compared between various CM and LM stimulus conditions. To compare those stimulus types with each other, the detection threshold was measured in one experiment to determine the visibility of each stimulus type, i.e. multiples above threshold. LM stimuli engage in significantly more exclusive visibility and trigger more alternation even when CM stimuli are of comparable visibility. Lower proportions of exclusive visibility and numbers of perceptual alternation for CM stimuli were due to greater proportions of superimposition. When comparably visible LM and CM stimuli compete with each other under binocular rivalry conditions, CM exclusive visibility predominates over LM exclusive visibility. Even if LM visibility is many times above CM visibility, LM stimuli never reach perceptual predominance. This result suggests that CM stimuli are processed unlike LM stimuli by neurones that receive initial binocular input. The results obtained were integrated into models concerning alternation dynamics and underlying processing sites for LM and CM stimuli.

Binocular rivalry can occur when incompatible stimuli are presented separately to the eyes. Since the invention of the stereoscope by Wheatstone in 1838, binocular rivalry has been intensively investigated with visual stimuli, which are differentiated from the background by variations in luminance, so-called luminance-modulated stimuli. However, it is also possible to perceive stimuli for which luminance of the target does not differ from that of the background but instead varies in contrast: so-called contrast-modulated (CM) stimuli. The main aim of this thesis is to investigate CM and noisy luminance-modulated (LM) stimuli under binocular rivalry conditions as the gained knowledge would enhance our understanding of both CM processing, as well as binocular rivalry. Perceptual change rates, proportions of exclusive visibility, mixed percepts (i.e. piecemeal and superimposition), as well as changes of these proportions across time and distributions of perceptual phases were calculated and compared between various CM and LM stimulus conditions. To compare those stimulus types with each other, the detection threshold was measured in one experiment to determine the visibility of each stimulus type, i.e. multiples above threshold. LM stimuli engage in significantly more exclusive visibility and trigger more alternation even when CM stimuli are of comparable visibility. Lower proportions of exclusive visibility and numbers of perceptual alternation for CM stimuli were due to greater proportions of superimposition. When comparably visible LM and CM stimuli compete with each other under binocular rivalry conditions, CM exclusive visibility predominates over LM exclusive visibility. Even if LM visibility is many times above CM visibility, LM stimuli never reach perceptual predominance. This result suggests that CM stimuli are processed unlike LM stimuli by neurones that receive initial binocular input. The results obtained were integrated into models concerning alternation dynamics and underlying processing sites for LM and CM stimuli.

Figure-ground segregation occurs when one of two regions sharing a border is perceived as a shaped entity (a figure) and the other is perceived as a shapeless background to the figure. The mechanism of figure-ground perception is inhibitory competition. Peterson and Skow (2008) showed that a familiar configuration that loses the competition for figural status is not perceived consciously and is suppressed, at least at the level of categorical shape. A remaining question is whether the semantics of the familiar configuration are also accessed and suppressed. The present study investigates this question through binocular rivalry. Binocular rivalry occurs when separate images are simultaneously presented to the left and right eyes. Typically one dominates at any given moment, and awareness alternates back and forth between these two images. The image that is not perceived is suppressed (Wheatstone, 1838). The present experiments investigated how the suppression in figure-ground perception and the suppression in binocular rivalry interact. In one eye, subjects viewed a silhouette that initially dominated because a dynamic, colorful pattern was presented within the confines of the figure. In the other eye, participants viewed a word string either a word that named a familiar configuration or a non-word; the letter string was initially suppressed. Experiment 1 explored whether the time required for the letter string to reach awareness between a silhouette that had a hidden, familiar configuration on the ground side or a silhouette with a novel configuration on the ground. Experiment 2 observed the time required to make a lexical decision once the letter string arrived to awareness. Both experiments failed to yield evidence for an interaction between figure-ground and binocular rivalry suppression. This suggests that during binocular rivalry, a shape suppressed by figure-ground competition fails to interact with a word corresponding to the suppressed shape.

Visual abnormalities, both at the sensory input and the higher interpretive levels, have been associated with many of the symptoms of schizophrenia. Individuals with schizophrenia typically experience distortions of sensory perception, resulting in perceptual hallucinations and delusions that are related to the observed visual deficits. Disorganised speech, thinking and behaviour are commonly experienced by sufferers of the disorder, and have also been attributed to perceptual disturbances associated with anomalies in visual processing. Compounding these issues are marked deficits in cognitive functioning that are observed in approximately 80% of those with schizophrenia. Cognitive impairments associated with schizophrenia include: difficulty with concentration and memory (i.e. working, visual and verbal), an impaired ability to process complex information, response inhibition and deficits in speed of processing, visual and verbal learning. Deficits in sustained attention or vigilance, poor executive functioning such as poor reasoning, problem solving, and social cognition, are all influenced by impaired visual processing. These symptoms impact on the internal perceptual world of those with schizophrenia, and hamper their ability to navigate their external environment. Visual processing abnormalities in schizophrenia are likely to worsen personal, social and occupational functioning. Binocular rivalry provides a unique opportunity to investigate the processes involved in visual awareness and visual perception. Binocular rivalry is the alternation of perceptual images that occurs when conflicting visual stimuli are presented to each eye in the same retinal location. The observer perceives the opposing images in an alternating fashion, despite the sensory input to each eye remaining constant. Binocular rivalry tasks have been developed to investigate specific parts of the visual system. The research presented in this Thesis provides an explorative investigation into binocular rivalry in schizophrenia, using the method of Pettigrew and Miller (1998) and comparing individuals with schizophrenia to healthy controls. This method allows manipulations to the spatial and temporal frequency, luminance contrast and chromaticity of the visual stimuli. Manipulations to the rival stimuli affect the rate of binocular rivalry alternations and the time spent perceiving each image (dominance duration). Binocular rivalry rate and dominance durations provide useful measures to investigate aspects of visual neural processing that lead to the perceptual disturbances and cognitive dysfunction attributed to schizophrenia. However, despite this promise the binocular rivalry phenomenon has not been extensively explored in schizophrenia to date. Following a review of the literature, the research in this Thesis examined individual variation in binocular rivalry. The initial study (Chapter 2) explored the effect of systematically altering the properties of the stimuli (i.e. spatial and temporal frequency, luminance contrast and chromaticity) on binocular rivalry rate and dominance durations in healthy individuals (n=20). The findings showed that altering the stimuli with respect to temporal frequency and luminance contrast significantly affected rate. This is significant as processing of temporal frequency and luminance contrast have consistently been demonstrated to be abnormal in schizophrenia. The current research then explored binocular rivalry in schizophrenia. The primary research question was, "Are binocular rivalry rates and dominance durations recorded in participants with schizophrenia different to those of the controls?" In this second study binocular rivalry data that were collected using low- and highstrength binocular rivalry were compared to alternations recorded during a monocular rivalry task, the Necker Cube task to replicate and advance the work of Miller et al., (2003). Participants with schizophrenia (n=20) recorded fewer alternations (i.e. slower alternation rates) than control participants (n=20) on both binocular rivalry tasks, however no difference was observed between the groups on the Necker cube task. Magnocellular and parvocellular visual pathways, thought to be abnormal in schizophrenia, were also investigated in binocular rivalry. The binocular rivalry stimuli used in this third study (Chapter 4) were altered to bias the task for one of these two pathways. Participants with schizophrenia recorded slower binocular rivalry rates than controls in both binocular rivalry tasks. Using a ‘within subject design’, binocular rivalry data were compared to data collected from a backwardmasking task widely accepted to bias both these pathways. Based on these data, a model of binocular rivalry, based on the magnocellular and parvocellular pathways that contribute to the dorsal and ventral visual streams, was developed. Binocular rivalry rates were compared with performance on the Benton’s Judgment of Line Orientation task, in individuals with schizophrenia compared to healthy controls (Chapter 5). The Benton’s Judgment of Line Orientation task is widely accepted to be processed within the right cerebral hemisphere, making it an appropriate task to investigate the role of the cerebral hemispheres in binocular rivalry, and to investigate the inter-hemispheric switching hypothesis of binocular rivalry proposed by Pettigrew and Miller (1998, 2003). The data were suggestive of intra-hemispheric rather than an inter-hemispheric visual processing in binocular rivalry. Neurotransmitter involvement in binocular rivalry, backward masking and Judgment of Line Orientation in schizophrenia were investigated using a genetic indicator of dopamine receptor distribution and functioning; the presence of the Taq1 allele of the dopamine D2 receptor (DRD2) receptor gene. This final study (Chapter 6) explored whether the presence of the Taq1 allele of the DRD2 receptor gene, and thus, by inference the distribution of dopamine receptors and dopamine function, accounted for the large individual variation in binocular rivalry. The presence of the Taq1 allele was associated with slower binocular rivalry rates or poorer performance in the backward masking and Judgment of Line Orientation tasks seen in the group with schizophrenia. This Thesis has contributed to what is known about binocular rivalry in schizophrenia. Consistently slower binocular rivalry rates were observed in participants with schizophrenia, indicating abnormally-slow visual processing in this group. These data support previous studies reporting visual processing abnormalities in schizophrenia and suggest that a slow binocular rivalry rate is not a feature specific to bipolar disorder, but may be a feature of disorders with psychotic features generally. The contributions of the magnocellular or dorsal pathways and parvocellular or ventral pathways to binocular rivalry, and therefore to perceptual awareness, were investigated. The data presented supported the view that the magnocellular system initiates perceptual awareness of an image and the parvocellular system maintains the perception of the image, making it available to higher level processing occurring within the cortical hemispheres. Abnormal magnocellular and parvocellular processing may both contribute to perceptual disturbances that ultimately contribute to the cognitive dysfunction associated with schizophrenia. An alternative model of binocular rivalry based on these observations was proposed.

Doctor of Philosophy
The human, along with other primates, has forward placed eyes, and an area of acute vision (the fovea) on each retina. The overlap of the visual fields and the hemi-decussation of the visual pathways at the optic chiasm provide the basis for binocular vision, in particular stereopsis, the accurate perception of the position of objects in three dimensional space and an improved ability to perceive the form of solid objects. An intricate system of eye movements is needed to achieve and maintain stable foveal fixation on each eye in an environment where visual targets vary in direction and depth, where the visual environment may be moving, the eyes or the rest of the body is moving. The purpose of this study is to evaluate the accuracy of binocular alignment for far and near fixations, under relatively natural conditions. To achieve binocular fixation, accurate vergence eye movements are required to align the eyes, and to maintain this alignment when a person changes fixation to objects situated at different distances from the eyes. ‘Pure’ vergence eye movements occur when these objects are situated along the mid sagittal plane, however, in natural conditions other eye movement systems are also involved. To understand the contribution of different eye movement systems to binocular fixation at different distances, the accuracy of binocular alignment in subjects with normal binocular single vision was evaluated in subjects with normal binocular vision under the following conditions • Fixation on targets along the mid sagittal plane (vergence eye movements only) • Fixation on targets displaced to either side of the mid sagittal plane (combined vergence eye movements and saccades • Fixation on earth fixed targets situated straight ahead in space, but with the head tilted to either side (combined vergence eye movements, saccades and torsional eye movements). The protocol for all experiments was approved by the Human Ethics Committee of the University of Sydney and followed the tenets of the Declaration of Helsinki. Throughout this thesis the term ‘binocular alignment’ will be used to describe the position of each eye during or following a change in vergence. The term ‘vergence error’ will refer to situations where the angle of vergence alignment is different from that required, so that the image of the fixation target does not fall on the fovea of one or both eyes.

The dissertation examines the problem of temporally uneven information processing in the nervous system. We chose binocular rivalry and ambiguous figure perception for our research, as these phenomena are pronounced examples of cyclical processes in perception. Binocular rivalry and ambiguous figure perception are cases in perception, when the subjective perception every few seconds vacillates between alternative interpretations, while the physical stimulation remains constant. Our research examines the relationship between these perception alterations and millisecond-order cycles of information processing in the nervous system. We created special equipment to present visual stimuli intermittently (flickering) and examined, whether the flickering rate of the stimuli influences the temporal characteristics (mean dominance duration) of binocular rivalry and ambiguous figure perception. The results confirmed the relationship, but also highlighted the temporal instability of binocular rivalry dominance durations.
Disertacijoje nagrinėjama informacijos apdorojimo procesų nervų sistemoje laikinio netolygumo problema. Tyrimui pasirinkti akių konkurencijos ir dviprasmių figūrų suvokimo reiškiniai, ryškiai atspindintys suvokimo procesų cikliškumą. Akių konkurencija ir dviprasmių figūrų suvokimas yra reiškiniai, kuomet fiziniam stimului nesikeičiant, subjektyvus suvokimas kas kelias sekundes kaitaliojasi tarp alternatyvių interpretacijų. Tyrime nagrinėjamas šių sekundinių suvokimo ciklų ryšys su milisekundžių eilės informacijos apdorojimo ciklais. Sukurta speciali aparatūra, kuria stimulai į akis buvo pateikti mirksintys nustatytu dažniu, ir tikrinta, ar stimulų mirksėjimo dažnis lemia akių konkurencijos ir dviprasmių figūrų suvokimo laikines savybes (vidutinę dominavimo trukmę). Rezultatai patvirtino šį ryšį, tačiau taip pat nustatyta, kad akių konkurencijos vidutinei dominavimo trukmei yra būdingas laikinis nestabilumas – dominavimo trukmė gana didele amplitude kinta kelių minučių, valandos ir kelių parų eigoje.

Thesis (Ph. D.)--University of Alabama at Birmingham, 2007.
Additional advisors: Timothy Gawne, Richard Gray, Michael Loop, Michael Sloane, Donald Twieg. Description based on contents viewed Mar. 3, 2008; title from title screen. Includes bibliographical references (p. 88-97).

In binocular rivalry, paradigms have been proposed for unobtrusive moment-by-moment readout of observers' perceptual experience (“no-report paradigms”). Here, we take a first step to extend this concept to auditory multistability. Observers continuously reported which of two concurrent tone sequences they perceived in the foreground: high-pitch (1008 Hz) or low-pitch (400 Hz) tones. Interstimulus intervals were either fixed per sequence (Experiments 1 and 2) or random with tones alternating (Experiment 3). A horizontally drifting grating was presented to each eye; to induce binocular rivalry, gratings had distinct colors and motion directions. To associate each grating with one tone sequence, a pattern on the grating jumped vertically whenever the respective tone occurred. We found that the direction of the optokinetic nystagmus (OKN)—induced by the visually dominant grating—could be used to decode the tone (high/low) that was perceived in the foreground well above chance. This OKN-based readout improved after observers had gained experience with the auditory task (Experiments 1 and 2) and for simpler auditory tasks (Experiment 3). We found no evidence that the visual stimulus affected auditory multistability. Although decoding performance is still far from perfect, our paradigm may eventually provide a continuous estimate of the currently dominant percept in auditory multistability.

When the two eyes are presented with sufficiently different images, Binocular Rivalry (BR) occurs. BR is a form of bistable perception involving stochastic alternations in awareness between distinct images shown to each eye. It has been suggested that the dynamics of BR are due to the activity of a central temporal process and are linked to involuntary mechanisms of selective attention (aka exogenous attention). To test these ideas, stimuli designed to evoke exogenous attention and central temporal processes were employed during BR observation. These stimuli included auditory and visual looming motion and streams of transient events of varied temporal rate and pattern. Although these stimuli exerted a strong impact over some aspects of BR, they were unable to override its characteristic stochastic pattern of alternations completely. It is concluded that BR is subject to distributed influences, but ultimately, is achieved in neural processing areas specific to the binocular conflict.

Diariamente recibimos mucha información que procede simultáneamente de distintos sentidos, que se combina en el cerebro para conseguir una respuesta rápida y precisa. Muchas veces, esto ocurre mediante la integración multisensorial. Sin embargo, ¿puede darse integración multisensorial en situaciones de emergencia, aunque los recursos cognitivos son ocupados? Para resolver esta cuestión, utilizamos estímulos audiovisuales presentados de forma repentina, sin contenido informativo en un paradigma de rivalidad binocular. Esto nos permitió medir la integración de abajo a arriba en una situación cuando los mecanismos de arriba abajo están limitados. Los hallazgos de esta tesis ponen en duda puntos de vista anteriores, ya que un beneficio intermodal en el comportamiento no resulta necesariamente de la integración de abajo a arriba sino que, primero, la contribución individual de cada uno de los estímulos puede explicar la facilitación intermodal y, segundo, no se puede descartar una influencia de la atención de abajo arriba.
In everyday life, we are bombarded with information coming simultaneously from different senses. The information is combined in the brain in order to achieve a fast and accurate answer with the least effort possible. Many times, it happens through multisensory integration. However, may multisensory integration occur (automatically) in emergency situations when imperative action is needed, even if the cognitive resources are deployed to other ongoing activities? In order to resolve the query, we capitalized on uninformative, unpredictive, abrupt audiovisual stimulation in binocular rivalry, which let us measure bottom-up multisensory integration in a situation where top-down mechanisms are limited or even absent. The findings of this dissertation challenge previous views about unaware multisensory integration, since a cross-modal behavioral benefit not necessarily derives from bottom-up multisensory integration, instead, first, the individual contribution of the stimuli might offer sufficient explanation for the cross-modal facilitation, second, the putative influence of bottom-up attention cannot be dismissed.

Disertacijoje nagrinėjama informacijos apdorojimo procesų nervų sistemoje laikinio netolygumo problema. Tyrimui pasirinkti akių konkurencijos ir dviprasmių figūrų suvokimo reiškiniai, ryškiai atspindintys suvokimo procesų cikliškumą. Akių konkurencija ir dviprasmių figūrų suvokimas yra reiškiniai, kuomet fiziniam stimului nesikeičiant, subjektyvus suvokimas kas kelias sekundes kaitaliojasi tarp alternatyvių interpretacijų. Tyrime nagrinėjamas šių sekundinių suvokimo ciklų ryšys su milisekundžių eilės informacijos apdorojimo ciklais. Sukurta speciali aparatūra, kuria stimulai į akis buvo pateikti mirksintys nustatytu dažniu, ir tikrinta, ar stimulų mirksėjimo dažnis lemia akių konkurencijos ir dviprasmių figūrų suvokimo laikines savybes (vidutinę dominavimo trukmę). Rezultatai patvirtino šį ryšį, tačiau taip pat nustatyta, kad akių konkurencijos vidutinei dominavimo trukmei yra būdingas laikinis nestabilumas – dominavimo trukmė gana didele amplitude kinta kelių minučių, valandos ir kelių parų eigoje.
The dissertation examines the problem of temporally uneven information processing in the nervous system. We chose binocular rivalry and ambiguous figure perception for our research, as these phenomena are pronounced examples of cyclical processes in perception. Binocular rivalry and ambiguous figure perception are cases in perception, when the subjective perception every few seconds vacillates between alternative interpretations, while the physical stimulation remains constant. Our research examines the relationship between these perception alterations and millisecond-order cycles of information processing in the nervous system. We created special equipment to present visual stimuli intermittently (flickering) and examined, whether the flickering rate of the stimuli influences the temporal characteristics (mean dominance duration) of binocular rivalry and ambiguous figure perception. The results confirmed the relationship, but also highlighted the temporal instability of binocular rivalry dominance durations.

For many years, artists and photographers have used blurred lines or `motion streaks' along an object's trajectory of motion to indicate fast motion. As it turns out, these streaks must occur in vision, because the visual system integrates information over time, around 100 - 120 ms. Generally streaks are not seen, but they could prove a useful cue to direction of motion, as suggested in an influential model proposed by Geisler (1999). In experiments exploiting the tilt aftereffect and illusion paradigms, we found that strong motion streaks produced robust tilt aftereffects and illusions, similar in magnitude and orientation tuning to those induced by tilted lines. These effects were weak or absent in weak streak conditions, and when motion was too slow to form streaks. We also investigated binocular rivalry suppression of static stimuli by fast and slow motion, and found that grating stimuli oriented parallel to the direction of fast, rivalling motions were more deeply suppressed than those orthogonal to the motion direction, but only for fast, `streaky' motion, not slow motion. We attributed this deeper suppression to within-channel masking by motion streaks, as there was clear orientation tuning of this effect, both during suppression and dominance phases. We further explored masking by motion streaks in two further studies addressing the orientation and spatial frequency tuning of dichoptic and monoptic masking by motion streaks. Finally, we used functional magnetic resonance imaging to explore the neural correlates of these streaks, and found similar patterns of activity for fast motion and static, oriented patterns, which could successfully be used by a classifier algorithm to decode whether a participant was viewing one of two directions of motion (45 or 135 degrees) after training on orientation sessions alone. Together, these results indicate that motion streaks produced by temporal integration of fast translating features effectively adapt orientation-selective cells, that they cause masking similar to that caused by static stimuli, that they can cause tuned suppression of oriented stimuli even when not seen, and that they are present in early visual cortex. Thus, motion streaks are present in the visual system, and would be available to perform the function ascribed to them by Geisler. This is discussed in terms of traditional models of motion perception, and some novel predictions and future experiments are proposed.

Les oscillations sont omniprésentes dans le cerveau. Une grande partie de la littérature soutient que les oscillations cérébrales ne sont pas un sous-produit des activités du cerveau ; en fait, elles façonnent notre perception en modulant l'excitabilité corticale et en facilitant les communications neuronales. Par conséquent, notre perception visuelle, notre attention et peut-être même notre conscience s'accroissent et diminuent au fil du temps. Cependant, le rôle des oscillations dans ces fonctions perceptives ou cognitives n'est pas entièrement compris. Pour la perception visuelle et l'attention, bien que la relation entre ces fonctions et les oscillations cérébrales ait été établie, on ne sait pas exactement où et comment ces oscillations cérébrales sont générées. En ce qui concerne la conscience, on ignore encore comment les oscillations sont impliquées dans la production de la perception consciente. Ce sont les questions que la présente thèse tente d'aborder. La thèse commence par des oscillations cérébrales dans la fonction cérébrale la plus élémentaire et la mieux comprise - la perception visuelle. Il a été suggéré que la perception visuelle est un processus oscillatoire, échantillonnant le monde à la fréquence alpha. Les échos perceptifs sont une démonstration de l'échantillonnage visuel. L'écho est une fonction de réponse impulsionnelle qui oscille à ~10 Hz en réponse à des stimuli de bruit blanc. Alors que les propriétés temporelles sont progressivement révélées, l'origine des échos reste floue. La première étude s'est attachée à étudier la base neurale des échos perceptifs, et nous avons découvert que les échos proviennent du cortex visuel primitif. Ensuite, nous passons à l'attention. Il a été démontré que l'attention échantillonne l'environnement à la fréquence thêta. Une étude sur les singes suggère que l'oscillation thêta de l'attention peut provenir des interactions compétitives du champ réceptif de V4. Pour savoir si ce mécanisme peut être généralisé aux humains, nous reproduisons l'expérience comportementale chez les humains. Enfin, dans les deux dernières études, nous examinons les oscillations du cerveau dans la conscience. En utilisant la rivalité binoculaire, nous cherchons d'abord à savoir si les échos perceptifs nécessitent une conscience. Les résultats montrent que les échos perceptifs peuvent être déclenchés à la fois lorsque le stimulus est dans la conscience et en dehors de la conscience. Ensuite, nous étudions le flux d'informations pendant la rivalité binoculaire et montrons une augmentation des activités bêta et thêta de haut en bas avant les commutations perceptuelles. En conclusion, le cerveau est un système dynamique dans lequel les oscillations facilitent de manière flexible diverses fonctions cérébrales en jouant différents rôles fonctionnels
Oscillations are ubiquitous in the brain. A large body of literature has supported that brain oscillations are not a by-product of brain activities; in fact, they shape our perception by modulating cortical excitability and facilitating neuronal communications. Consequently, our visual perception, attention and maybe even consciousness wax and wane across time. However, the role of oscillations in these perceptual or cognitive functions is not entirely understood. For visual perception and attention, although the relationship between them and brain oscillations has been established, it is unclear where and how these brain oscillations are generated. As for consciousness, how the oscillations are involved in producing conscious perception remains unknown. These are the questions the current thesis attempts to address. The thesis starts with brain oscillations in the most basic and best understood brain function - visual perception. It has been suggested that visual perception is an oscillatory process, sampling the world at the alpha frequency. Perceptual echoes are one demonstration of visual sampling. The echo is an impulse response function that oscillates at ~10 Hz in response to white-noise stimuli. While the temporal properties are gradually revealed, the origin of the echoes remains unclear. The first study set out to study the neural basis of perceptual echoes, and we found the echoes originate in the early visual cortex. Next, we move on to attention. It has been shown that attention samples the environment at theta frequency. A monkey study suggests that the theta oscillation of attention may arise from competitive receptive field interactions of V4. To investigate if the mechanism can be generalized to humans, we replicate the behavioral experiment in humans. Finally, in the last two studies, we examine brain oscillations in consciousness. Utilizing binocular rivalry, we first investigate if the perceptual echoes require consciousness. The results show that perceptual echoes can be elicited both when the stimulus is in consciousness and out of consciousness. Second, we investigate information flow during binocular rivalry and show an increased top-down beta and theta activities before perceptual switches. In conclusion, the brain is a dynamic system in which the oscillations flexibly facilitate various brain functions by playing different functional roles

Les visuels de casque monoculaires utilisés dans l'aéronautique augmentent la vision des pilotes et facilitent l'accès aux informations essentielles telles que la symbologie de vol. Ils sont plus légers et plus ajustables que leurs homologuesbinoculaires, peuvent s'intégrer dans n'importe quel aéronef et permettent de conserver l'information quelle que soit la direction de regard. Cependant, ils génèrent une perception particulière puisqu'une image virtuelle monoculaire se superpose à l'environnement réel binoculaire. Des informations différentes sont projetées à des régions correspondantes des deux yeux créant un conflit interoculaire. L'enjeu de cette thèse est d'évaluer l'impact des caractéristiques des stimuli sur les performances aux tâches réalisées via ce type de système afin d'en optimiser l'utilisation.Deux études psychophysiques et une étude écologique en simulateur de vol ont été réalisées. Toutes ont montré un bon confort à l'exposition. Les performances ont été évalués en fonction des caractéristiques du fond binoculaire, de l'affichage de l'image monoculaire et des caractéristiques d'évènements à détecter. Le choix de l'œil de présentation n'est pas anodin étant donné les différences entre les performances réalisées avec le monoculaire sur chacun des deux yeux. Nos résultats aux trois études montrent également que, comme pour deux images fusionnables ou dichoptiques, les performances sont dépendantes des stimulations visuelles. Ils suggèrent donc qu'il faille envisager une symbologie adaptative qui ne peux se résumer au changement de luminosité dont dispose actuellement les pilotes
Monocular augmented reality devices are used in the aeronautical field to enhance pilots' vision by providing access to essential information such as flight symbology. They are lighter and more adjustable than their binocular counterparts, can be integrated into any aircraft, and allow information to be retained regardless of gaze direction. However, they generate a particular perception since a monocular virtual image is superimposed on the real binocular environment. Different information is projected to corresponding regions of the two eyes creating an interocular conflict. The goal of this thesis is to evaluate the impact of the stimuli characteristics on the performance of tasks performed with this type of system to optimize its use. Two psychophysical studies and an ecological study in a flight simulator have been carried out. All of them showed a good comfort when exposed to interocular conflict. The performances were evaluated according to the characteristics of the binocular background, the display of the monocular image and the characteristics of events to be detected. The choice of the presenting eye is not insignificant given the differences between the performances achieved with the monocular on each of the two eyes. Our results from the three studies also show that, as with two fusible or two dichoptic images, performance is dependent on visual stimuli. They therefore suggest that an adaptive symbology should be considered, which cannot be summarized by the change in brightness currently available to pilots

Fluctuations in perceptual decisions emerge when our brain confronts with ambiguous sensory stimuli. For instance, our perception alternates between two conflicting images when presented dichoptically to our eyes, allowing a dissociation of the sensory stimulation from the conscious visual perception, and therefore providing a gateway to consciousness. How does the brain work when it deals with such ambiguous sensory stimuli? We addressed this question theoretically by employing a biophysically realistic attractor network, by consistently reducing it to a four- variable rate- based model, and by extracting analytical expressions for second- order statistics. We considered human behavioral and macaque neurophysiological data collected when subjects were confronting with such ambiguities. Our results show the relevance of neuronal adaptation in perceptual decision making, as well as that it contributes to the speed- accuracy trade- off. Furthermore, our findings affirm that both noise and neural adaptation operate in balance during the fluctuating states of visual awareness and suggest that while adaptation in inhibition is not relevant for the perceptual alternations, it contributes to the brain dynamics at rest. Finally, we explain the observed neuronal noise- decorrelation during visual consciousness and provide insights on the long- standing question: where in the brain rivalry is resolved.
Les fluctuacions en les decisions perceptives sorgeixen quan el nostre cervell s'enfronta a estímuls sensorials ambigus. Per exemple, la nostra percepció alterna entre dues imatges contradictòries quan es presenten de forma dicòptica als nostres ulls, cosa que permet una dissociació de l'estimulació sensorial de la percepció visual conscient, i per tant proporciona una porta d'entrada a la consciència. Com funciona el cervell quan es tracta d'aquest tipus d'estímuls sensorials ambigus? Hem tractat aquesta qüestió de forma teòrica mitjançant l'ús d'una xarxa d'atractors biofísicament realista, reduint-la de forma consistent a un model de quatre variables basat en la freqüència, i extraient expressions analítiques pels estadístics de segon ordre. Hem emprat dades neurofisiològiques de comportament d'humans i macacos recollides quan els subjectes s'enfrontaven a aquest tipus d'ambigüitats. Els nostres resultats mostren la importància de l'adaptació neuronal en la presa de decisions perceptives i mostren la seva contribució a l'equilibri velocitat-precisió. D'altra banda, els nostres resultats confirmen que tant el soroll com l'adaptació neural operen en equilibri durant els estats fluctuants de consciència visual i suggereixen que, si bé l'adaptació en la inhibició no és rellevant per a les alternances de percepció, contribueix a la dinàmica del cervell en repòs. Finalment, expliquem la decorrelació del soroll neuronal observada durant la consciència visual i proporcionem noves idees en relació a l’antiga qüestió de en quin lloc del cervell es resol la rivalitat visual.

Doctor of Philosophy
Binocular rivalry refers to the perceptual alternation that occurs while viewing incompatible images, in which one monocular image is dominant and the other is suppressed. Rivalry has been closely studied but the neural site at which it is initiated is still controversial. The central claim of this thesis is that primary visual cortex is responsible for its initiation. This claim is supported by evidence from four experimental studies. The first study (described in Chapter 4) introduces the methodology for measuring visual sensitivity during dominance and suppression and compares several methods to see which yields the greatest difference between these two sensitivities. Suppression depth was measured by comparing the discrimination thresholds to a brief test stimulus delivered during dominance and suppression phases. The deepest suppression was achieved after a learning period, with the test stimulus presented for 100 ms and with post-test masking. The second study (Chapter 5) compares two hypotheses for the mechanism of binocular rivalry. Under eye suppression, visibility decreases when the tested eye is being suppressed, regardless of the test stimulus’s features. Feature suppression, however, predicts that reduction of visibility is caused by suppression of a stimulus feature, no matter which eye is suppressed. Eye suppression claims that monocular channels in the visual system alternate between dominance and suppression, while Feature suppression assumes that the features of stimuli inhibit each other perceptually in the high-level cortex. The experiment used a test stimulus similar in features to one, but not the other, rivalry-inducing stimulus. Test sensitivity was found to be lowered when the test stimulus was presented to the eye whose rivalry-inducing stimulus was suppressed. Sensitivity was not lowered when the test stimulus was presented to the other eye, even when the test shared features with the suppressed stimulus. The conclusion is that feature suppression is weak or does not exist without eye suppression, and that rivalry therefore originates in the primary visual cortex. If binocular rivalry is initiated in the primary visual cortex, stimuli producing no coherent activity in that area should produce no rivalry. In the third study (Chapter 6) this idea was tested with rotating arrays of short-lifetime dots. The dots with the shortest lifetime produced an image with no rotation signal, and an infinite lifetime produced rigid rotation. Subjects could discriminate the rotation direction with high accuracy at all but the shortest lifetime. When the two eyes were presented with opposite directions of rotation, there was binocular rivalry only at the longest lifetimes. Stimuli with short lifetimes produce a coherent motion signal, since their direction can be discriminated, but do not produce rivalry. A simple interpretation of this observation is that binocular rivalry is initiated at a level in the visual hierarchy below that which supports the motion signal. The model supported by the results of previous chapters requires that binocular rivalry suppression be small in the primary visual cortex, and builds up as signals progress along the visual pathway. This model predicts that for judgements dependent on activity in high visual cortex: 1. Binocular rivalry suppression should be deep; 2. Responses should be contrast invariant. The fourth and last study (chapter 7) confirmed these predictions by measuring suppression depth in two ways. First, two similar forms were briefly presented to one eye: the difference in shapes required for their discrimination was substantially greater during suppression than during dominance. Second, the two forms were made sufficiently different in shape to allow easy discrimination at high contrast, and the contrast of these forms was lowered to find the discrimination threshold. The results in the second experiment showed that contrast sensitivity did not differ between the suppression and dominance states. This invariance in contrast sensitivity is interpreted in terms of steep contrast-response functions in cortex beyond the primary visual area. The work in this thesis supports the idea that binocular rivalry is a process distributed along the visual pathway. More importantly, the results provide several lines of evidence that binocular rivalry is initiated in primary visual cortex.

When stimuli presented to the two eyes differ considerably, stable binocular fusion fails, and the subjective percept alternates between the two monocular images, a phenomenon known as binocular rivalry. The influence of attention over this perceptual switching has long been studied, and although there is evidence that attention can affect the alternation rate, its role in the overall dynamics of the rivalry process remains unclear. The present study investigated the relationship between the attention paid to the rivalry stimulus, and the dynamics of the perceptual alternations. Specifically, the temporal course of binocular rivalry was studied as the subjects performed difficult nonvisual and visual concurrent tasks, directing their attention away from the rivalry stimulus. Periods of complete perceptual dominance were compared for the attended condition, where the subjects reported perceptual changes, and the unattended condition, where one of the simultaneous tasks was performed. During both the attended and unattended conditions, phases of rivalry dominance were obtained by analyzing the subject"s optokinetic nystagmus recorded by an electrooculogram, where the polarity of the nystagmus served as an objective indicator of the perceived direction of motion. In all cases, the presence of a difficult concurrent task had little or no effect on the statistics of the alternations, as judged by two classic tests of rivalry, although the overall alternation rate showed a small but significant increase with the concurrent task. It is concluded that the statistical patterns of rivalry alternations are not governed by attentional shifts or decision-making on the part of the subject.

博士
國立臺灣大學
心理學研究所
95
The function of human visual system is to analyze the input image and to extract information about objects in the environment. It puzzles investigators for years how human visual system is capable of reconstructing a stable and coherent three-dimensional world through two-dimensional retinal information. A collection of incident lights into our eyes can be interpreted as numerous possible objects, but most of the time, people are consciously aware of a single percept. It results from a series of processes and distributed neural networks are implicated to process incoming visual information. Hence, any impairment among the processes may prevent daily vision. For instance, macular degeneration causes loss of central vision, which harms one’s capability to see fine details of an object (Cacho, Dickinson, Reeves, & Harper, 2007). Damage to unilateral primary visual cortex leads to blindness of the contralateral visual field (Trevethan, Sahraie, & Weiskrantz, 2007). However, some patients seemed to exhibit residual visual ability unconsciously, which is called “blindsight”. Although patients insisted on their visual deficits, some of them performed better than chance when they were required to guess whether a stimulus was presented in their blind field (Trevethan et al., 2007). It has raised a lot of discussion of visual awareness and its neural correlates (Crick & Koch, 1998). To a normal brain, a stable percept is the best guess given the visual input (Crick & Koch, 2003). Occasionally, the stable percept may break down. Certain categories of visual stimuli lead to two or more percepts, rather than one, and those percepts alternate without any physical changes occurring in the stimulus. This phenomenon is called “bistable perception” or “multistable perception”, depending on how many percepts the stimulus evokes (Blake & Logothetis, 2002; Leopold & 9 Logothetis, 1999). Perceptual changes which lack corresponding stimulus changes offer an opportunity to dissociate perceptual representation from sensory representation of a stimulus (Moutoussis, Keliris, Kourtzi, & Logothetis, 2005), and address to the issue of visual awareness (Crick & Koch, 2003). Ambiguous figure is one type of stimuli which is capable of generating bistable perception. For example, the famous Necker cube, as Figure 1a shows, can be perceived as two cubes with different depth features (see Figure 1b & 1c). Continuously viewing it for a while results in a dynamic sequence of the two cube percepts. Binocular rivalry is another type of stimuli which also induces bistable perception. When two discrepant monocular images presented to two eyes separately, the two images rival for perceptual dominance and only one monocular image is perceived at a time while the other is suppressed. Figure 2 illustrates an example of binocular rivalry, in which the two gratings moving in the opposite directions would lead to perceptual alternations between one and the other. Although both binocular rivalry and ambiguous figure cause two percepts switching, they differ in how alternative percepts arise. In the above examples, the Necker cube needs reorganization of edges, so as to coherently construct it into the other depth, but different values of a feature, such as motion directions, for two eyes are sufficient to cause alternative percepts without further grouping.

How does the neuronal activity in our brains give rise to our perceptions? We recorded the electrophysiological activity of over one thousand individual neurons in the human brain during object recognition, binocular rivalry, visual imagery and sleep. Subjects were patients with intractable epilepsy implanted with depth electrodes in targets including the amygdala, entorhinal cortex and hippocampus to localize the seizure focus for potential surgical resection. This has allowed us to explore the neuronal responses during visual processing in humans at an unprecedented level of spatial and temporal resolution. We observed a high degree of selectivity in the responses to complex visual stimuli. Some units were selective to categories of pictures including faces, houses, objects, famous people and animals while others responded only to one or a few stimuli, suggesting a sparse representation of visual information in the medial temporal lobe. Most of the selective neurons modulated their responses depending on the subject's percept during flash suppression. To further explore the correlation between perception and neuronal activity we investigated the vivid images that can be voluntarily generated in our minds in the absence of concomitant visual input. Our study revealed neuronal correlates of visual imagery and supports a common substrate for the processing of visual input and recall. Since visual memory is also prominent during dreams, we investigated the neuronal responses during different stages of the sleep-wake cycle. We observed an increase in synchrony during slow wave sleep compared to the wake and rapid-eye-movement sleep states. Our results suggest that neuronal activity in the human medial temporal lobe correlates with perception, shows a strong degree of invariance to changes in the input and could be involved in processing, storing and recalling visual information.

碩士
國立臺灣科技大學
應用科技研究所
100
Three-dimension (3D) movie became popular since the 3D movie “Avatar” released in 2010. 3D display technology and related applications emerge and develop rapidly, but the 3D TV market is growing slowly. It means there are some factors making 3D TV not yet been wide-accepted. The primary two reasons are: (1) limited 3D programs, and (2) it causes visual discomfort when consumers are watching 3D video content for a long time. People feel the visual discomfort is partly invoked by 3D Crosstalk and Binocular Color Rivalry (BCR) of 3D images. The aim of this study is to assess the visual comfort (VC) of 3D crosstalk thresholds and binocular color-rivalry thresholds for 3D displays Previous studies on 3D Crosstalk focused on how to define 3D Crosstalk or to estimate the impact of 3D Crosstalk on visual comfort and image quality (IQ). The present study investigated the impact of binocular disparity angles (BD), background contrast, sharpness on visual comfort and ghosting by a series of psycho-visual experiments. The experimental results showed that, (1) BD has significant impact on VC. The 3D Crosstalk has no impact on VC when the amount of BD is less, but when binocular disparity angle is less than 1.5 degrees, the increasing of 3D Crosstalk will decrease the VC value. (2) Ghosting is not highly correlated to VC. Even significant ghosting can be observed, the VC value does not decline in proportion. (3) The recommended tolerance of 3D crosstalk is 2.5%. (4) Image sharpening is not recommended for displaying 3D images. In the CR study, the Just Noticeable Difference (JND) thresholds of the Visual Comfort (VC) were investigated pychovisually for 7 types of between-eye image differences including luminance, gamma, contrast, color temperature, chroma, hue and random tone differences. The experimental results show that: (1) the VC threshold values are higher when increasing the luminance and color temperature differences between two-views, (2) changing contrast or hue to single view resulting in low threshold values indicates the type of differences easily inducing binocular rivalry, and (3) luminance adaptation and chromaticity adaptation play important role on the variations of VC thresholds. Applying CIECAT02 (CIE Chromatic Adaption Transform 2002) to each view before calculating the between-eye color differences could reduce the variations.

碩士
國立高雄大學
應用數學系碩士班
102
In this thesis, we utilize Monte Carlo simulation method to study the effect of white noise on the qualitative behavior of adaptive winner-take-all neural network model, and try to use the simulation results to characterize the effect of white noise on the dynamical mechanisms underlying the random switching of visual perception in the binocular rivalry phenomenon. By observing and characterizing the qualitative change in the empirical probability density functions of simulated data, we find that the white noise intensity can make the system to generate so-called phenomenological bifurcation, which makes a transition for the system from fluctuation around the stable state random switching between two states. Also, we find that the increase of white noise intensity can lead to a change for the range at which the phenomenological bifurcation occurs for one important dynamical parameter--adaptation strength. Furthermore, under the assumption of Gaussian approximation, we derive the first and second order moment equations for the stochastic differential equations, which can provide an analytic tool for advanced bifurcation analysis of the system in the future.

Olfactory sensing is ubiquitous across animals and important for survival. Yet, its characteristics, mechanisms, and functions in humans remain not well understood. In this dissertation, I present four studies on human olfactory perception. Study I investigates the impact of short-term exposures to an odorant on long-term olfactory learning and habituation, while Study II examines human ability to localize smells; Study III probes visual-olfactory integration of object representations, and Study IV explores the role of olfaction in sensing nutrients. Several conclusions are drawn from these studies. First, brief intermittent exposures to even a barely detectable odorant lead to long-term incremental odorant-specific habituation. Second, humans localize smells based on gradient cues between the nostrils. Third, there is a within-hemispheric advantage in the integration of visual-olfactory object representations. Fourth, olfaction partakes in nutrient-sensing and facilitates the detection of food. Some broader implications of our findings are discussed.

Nell’apparentemente semplice processo di “vedere” sono coinvolti meccanismi neurali complessi, non del tutto compresi. La percezione visiva consiste di due componenti chiave: l’analisi dell’informazione e la consapevolezza soggettiva. Questa tesi riporta degli esperimenti comportamentali aventi lo scopo di far luce su due condizioni in cui l’esperienza e la sensazione percettiva sono dissociate: l’immaginazione e la soppressione visiva. IL CASO DELL'IMMAGINAZIONE VISIVA Una questione da lungo dibattuta è se la percezione ed immaginazione visiva condividono analoghi meccanismi cognitivi e neurali. Per chiarire questo problema abbiamo confrontato gli effetti di stimoli visivi reali e generati mentalmente sul tempo di reazione semplice (TR). In cinque esperimenti sono stati studiati gli effetti di differenze in luminanza, contrasto, frequenza spaziale, velocità di movimento ed orientamento. Con l’interessante eccezione della frequenza spaziale, in tutti gli altri compiti, percezione ed immaginazione hanno mostrato effetti qualitativamente simili. E’stata trovata una corrispondenza fra gli effetti al compito percettivo ed immaginativo per luminanza, contrasto, velocità di movimento ed orientamento di linee. Diversamente, l’interazione fra frequenza spaziale e compito era significativa: le risposte erano più veloci per reticoli di bassa rispetto ad alta frequenza spaziale solo per gli stimoli presentati visivamente. Il presente studio, dunque, mostra come variabili dipendenti di base esercitino simili effetti sul TR sia quando gli stimoli sono presentati visivamente che immaginati. Tali risultati sono indubbiamente a favore di una sovrapposizione fra le rappresentazioni strutturali della percezione e dell’immaginazione visiva. IL CASO DELLA SOPPRESSIONE VISIVA Quando gli input provenienti dai due occhi sono incompatibili e non possono essere fusi in un singolo percetto coerente, si verifica un fenomeno chiamato rivalità binoculare. Gli input visivi raggiungono alternativamente la consapevolezza per pochi secondi cosicché mentre un percetto è visibile, cioè dominante, l’altro è invisibile, cioè soppresso. I meccanismi neurali sottostanti la rivalità binoculare sono ampiamente dibattuti. Dati recenti mostrano una correlazione fra l’attività nella corteccia striata e lo stato percettivo riportato soggettivamente. Ad ogni modo, si sa ancora poco sul ruolo degli stadi di elaborazione precoce a livello sottocorticale. La presente Tesi fornisce una prova del coinvolgimento della via sottocorticale durante la rivalità binoculare. Il paradigma sperimentale impiegato è l’effetto degli stimoli ridondanti (noto come redundant target effect, RTE) con stimoli presentati in modo da generare una rivalità binoculare. Il RTE consiste nella maggiore velocità a rispondere a due (o più) target, rispetto ad uno solo. Tale effetto è mediato da un processo di sommazione spaziale in cui le strutture sottocorticali, compreso probabilmente il collicolo superiore, hanno un ruolo importante. In questo studio, abbiamo presentato dei Gabor in modo tale da generare una rivalità binoculare in un lato del punto di fissazione e una fusione nell’altro. Il/I target era/erano un incremento di contrasto del/i Gabor, che poteva essere visto oppure soppresso. L’effetto dello stesso target ridondante è stato confrontato quando questo era nella fase di dominanza e di soppressione. Il RTE trovato quando il target ridondante era dominante scompariva quando lo stesso target era percettivamente soppresso. Poiché il RTE era attribuibile ad una coattivazione neurale, tale dato suggerisce che il processo di soppressione coinvolge la via neurale del RTE. Questi risultati sono in linea con l’idea che la soppressione binoculare coinvolga processi visivi a stadi precoci, probabilmente antecedenti alla corteccia visiva primaria.
Behind the apparently simple process of “seeing”, there are complex neural mechanisms involved that are not completely understood. Visual perception consists of two key components: information analysis and subjective awareness. This thesis reports some behavioural experiments to cast further light on two conditions in which perceptual experience and sensation are dissociated: visual imagery and visual suppression. THE CASE OF VISUAL IMAGERY: A long standing issue is whether perception and mental imagery share similar cognitive and neural mechanisms. To cast further light on this problem we compared the effects of real and mentally generated visual stimuli on simple reaction time (RT). In five experiments we tested the effects of difference in luminance, contrast, spatial frequency, motion and orientation. With the intriguing exception of spatial frequency in all other tasks perception and imagery showed qualitatively similar effects. We found a correspondence between perception and imagery effects for luminance, contrast, speed of motion, and line orientation. In contrast, we found an interaction between perception and imagery for spatial frequency: gratings of low spatial frequency were responded to more quickly than those of higher spatial frequency only for visually presented stimuli. Thus, the present study shows that basic dependent variables exert similar effects on visual RT either when retinally presented or imagined. The present results undoubtedly provide support for some overlap between the structural representation of perception and imagery. THE CASE OF VISUAL SUPPRESSION: Binocular rivalry occurs when the inputs from the two eyes are incompatible and cannot be fused into a single, coherent percept. The visual inputs reach alternatively consciousness for a few seconds and while one percept is seen (dominant) the other is invisible (suppression). The neural mechanisms underlying binocular rivalry have been much debated. Recent evidence shows a correlation between the activity in the striate cortex and the subjectively reported state of rivalry. However, little is known about the role of subcortical processing stages. Here we provide evidence for an involvement of subcortical pathways during binocular rivalry. To this purpose, we employed the redundant target effect (RTE) with stimuli undergoing binocular rivalry. RTE simply means that response to two (or more) targets is faster than to one. It is mediated by a spatial summation process where subcortical structures, likely involving the superior colliculus, play an important role. In this study, Gabors were presented in a way to generate binocular rivalry on one side and fusion on the other side of the fixation cross. Target/s was/were a contrast increment of the Gabor that could be visible or perceptually suppressed. The effects of the same redundant target were compared when it was dominant and it was suppressed. The RTE found when the redundant target was dominant disappeared when the same target was perceptually suppressed. Since the RTE was ascribable to a neural coactivation, the present finding suggests that visual suppression involves the RTE pathway. These results support the idea that binocular suppression involves visual processes at early stages, prior to the primary visual cortex.

Gdy dwa różne obrazy prezentowane są oddzielnie do każdego oka, dochodzi do ich naprzemiennego pojawiania się w świadomości (tzw. rywalizacji obuocznej). Dotychczasowe badania wykazały, że dodatkowa ekspozycja na sygnały pochodzące z innych zmysłów wydłużać może czas postrzegania zgodnych z nimi obrazów. Pomimo wykształconej zdolności do przewidywania percepcyjnych skutków własnych działań, dowody na rzecz analogicznego wpływu aktywności sensomotorycznej na świadomość wzrokową są skąpe i pochodzą głównie z badań nad manualnymi ruchami dłoni. Celem prezentowanego projektu było sprawdzenie, czy całościowy ruch ciała zwiększać może dostępność percepcyjną zgodnych z nim bodźców podczas rywalizacji obuocznej. W serii przeprowadzonych badań osoby badane poruszały się na bieżni w różnych kierunkach oraz z różną prędkością, obserwując realistyczne wizualizacje przemieszczania się w wirtualnym tunelu. Postawiono hipotezę, że przepływy optyczne zgodne z parametrami własnego ruchu postrzegane będą dłużej niż przepływy z nimi niezgodne. Przewidywano również, że efekty te będą silniejsze u osób o wyższym poziomie zdolności proprioceptywnych. Otrzymane wyniki nie wykazały efektu zwiększonej dostępności percepcyjnej przepływów optycznych zgodnych z kierunkiem chodu, wskazały natomiast na priorytetyzację przepływów optycznych zgodnych z jego prędkością. Nie zaobserwowano związku między miarami wrażliwości proprioceptywnej a podatnością na postrzeganie bodźców zgodnych z własnym ruchem. Uzyskane rezultaty są zbieżne z doniesieniami sugerującymi ograniczoną i selektywną rolę aktywności sensomotorycznej w kształtowaniu treści wrażeń wzrokowych – podczas gdy zgodność przestrzenna nie wydaje się odgrywać istotnej roli, obserwuje się preferencyjne przetwarzanie bodźców odzwierciedlających dynamikę własnych działań.
When two dissimilar images are presented separately to each eye, one experiences continuous alternations between them – a phenomenon known as binocular rivalry. Prior studies showed that exposure to signals from other senses can prolong the access of stimulation-congruent images to visual awareness. Even though we are able to infer expected sensory consequences from our own movements, evidence that sensorimotor activity has an analogous impact on visual awareness is scarce and mainly confined to research on manual actions. The goal of the project was to investigate whether global bodily movement can increase perceptual dominance of locomotion-consistent stimuli during binocular rivalry. In a series of studies, participants walked on a treadmill in different directions and at different speeds while viewing highly realistic visualizations of self-motion in a virtual tunnel. It had been hypothesized that optic flows congruent with the parameters of locomotion will be perceived for a longer period of time than incongruent flows. In addition, these effects were expected to be more pronounced in individuals with better proprioceptive abilities. The results did not show evidence for enhanced perceptual access to optic flows congruent with direction of walking, whereas they did indicate perceptual prioritization of optic flows that were consistent with velocity of self-motion. No association was found between measures of proprioceptive sensitivity and propensity to observe locomotion-consistent percepts. The main findings concur with the emerging evidence for the limited and selective role of sensorimotor activity in clarifying the contents of visual awareness – whereas spatial congruence does not seem to play a salient role, the preferential processing of stimuli coupled to the dynamics of one’s action is observed.