Perceptual organization and consciousness

With chapter written by leading researchers in the field, this is the state-of-the-art reference work on this topic, and will be so for many years to come

An Integrated Framework of Spatiotemporal Dynamics of Binocular Rivalry

Fluctuations in perceptual dominance during binocular rivalry exhibit several hallmark characteristics. First, dominance switches are not periodic but, instead, stochastic: perception changes unpredictably. Second, despite being stochastic, average durations of rivalry dominance vary dependent on the strength of the rival stimuli: variations in contrast, luminance, or spatial frequency produce predictable changes in average dominance durations and, hence, in alternation rate. Third, perceptual switches originate locally and spread globally over time, sometimes as traveling waves of dominance: rivalry transitions are spatiotemporal events. This essay (1) reviews recent advances in our understanding of the bases of these three hallmark characteristics of binocular rivalry dynamics and (2) provides an integrated framework to account for those dynamics using cooperative and competitive spatial interactions among local neural circuits distributed over the visual field's retinotopic map. We close with speculations about how that framework might incorporate top-down influences on rivalry dynamics

Interocular induction of illusory size perception

Background: The perceived size of objects not only depends on their physical size but also on the surroundings in which they appear. For example, an object surrounded by small items looks larger than a physically identical object surrounded by big items (Ebbinghaus illusion), and a physically identical but distant object looks larger than an object that appears closer in space (Ponzo illusion). Activity in human primary visual cortex (V1) reflects the perceived rather than the physical size of objects, indicating an involvement of V1 in illusory size perception. Here we investigate the role of eye-specific signals in two common size illusions in order to provide further information about the mechanisms underlying illusory size perception.Results: We devised stimuli so that an object and its spatial context associated with illusory size perception could be presented together to one eye or separately to two eyes. We found that the Ponzo illusion had an equivalent magnitude whether the objects and contexts were presented to the same or different eyes, indicating that it may be largely mediated by binocular neurons. In contrast, the Ebbinghaus illusion became much weaker when objects and their contexts were presented to different eyes, indicating important contributions to the illusion from monocular neurons early in the visual pathway.Conclusions: Our findings show that two well-known size illusions - the Ponzo illusion and the Ebbinghaus illusion - are mediated by different neuronal populations, and suggest that the underlying neural mechanisms associated with illusory size perception differ and can be dependent on monocular channels in the early visual pathway

Binocular interactions in human vision

Early visual processing is subject to binocular interactions because cells in striate cortex show binocular responses and ocular dominance (Hubel & Weisel, 1968). The work presented in this thesis suggests that these physiological interactions can be revealed in psychophysical experiments using normal human observers. In the region corresponding to the blind spot, where binocular interactions differ from areas of the visual field which are represented by two eyes, monocular contrast sensitivity is increased. This finding can be partially explained by an absence of normal binocular interactions in this location (Chapter 2). A hemianopic patient was studied in an attempt to discover whether the effect in normal observers was mediated by either a mechanism in striate cortex or via a subcortical pathway. However, the results were unable to distinguish between these two explanations (Chapter 3).In a visual search task, no difference in reaction time was observed for targets presented to the region corresponding to the blind spot compared with targets presented to adjacent binocularly represented areas of the visual field. Since performance was unaffected by the monocularity of the region corresponding to the blind, pop-out for orientation may be mediated beyond striate cortex where cells are binocularly balanced (Chapter 5). Further support for this contention was provided by studies of orientation pop-out in central vision which found that dichoptic presentation of stimuli did not affect the degree of pop-out obtained and that in general, visual search for a target based solely on eye of origin is impossible (Chapter 6). However, a task that measured orientation difference sensitivity more directly than the search experiments, found that thresholds were higher for dichoptically presented stimuli. This suggests the involvement of neurons that receive a weighted input from each eye. A model of orientation difference coding can account for the results by assuming that the range of inhibition across which orientation differences are coded is narrower for dichoptic stimuli leading to a greater resolvable orientation difference (Chapter 7)

Engineering data compendium. Human perception and performance. User's guide

The concept underlying the Engineering Data Compendium was the product of a research and development program (Integrated Perceptual Information for Designers project) aimed at facilitating the application of basic research findings in human performance to the design and military crew systems. The principal objective was to develop a workable strategy for: (1) identifying and distilling information of potential value to system design from the existing research literature, and (2) presenting this technical information in a way that would aid its accessibility, interpretability, and applicability by systems designers. The present four volumes of the Engineering Data Compendium represent the first implementation of this strategy. This is the first volume, the User's Guide, containing a description of the program and instructions for its use

Spatial context in the early visual system

Important visual objects in our everyday life, such as fellow people, passing cars or birds perhaps, are not point-like structures but often occupy considerable amounts of the visual field. However, each photoreceptor in our eyes samples just a tiny portion of the visual field and somehow the visual system should integrate these local signals. This process takes place mainly in the visual cortex and, while higher-order visual areas play an important role in perception of extended structures, it is now well established that visual neurons at the first cortical steps of seeing integrate broad spatial context into their responses. The main purpose of this thesis was to provide detailed information concerning the spatial structure of the mechanisms that underlie integration of spatial context in the early visual system. The opening study of this thesis showed that the antagonistic Gaussians structure that has been used for modeling context integration in single visual neurons provides a relatively accurate description of the process also in the human visual system. The first study introduced a novel method for connecting perceptual and neuroimaging measurements and this method was applied in the second study of this thesis. The second study showed that the human visual system integrates spatial context in terms of its visual field size instead of the size of its cortical representation. The third study showed that context is integrated over an unexpectedly large region of the visual field and that spatially distant context may sometimes increase the contrast response of the visual system. The closing study showed that orientation specificity of the integration of spatial context depends on distance both in single neurons in the macaque primary visual cortex and in human perception. The knowledge acquired in this thesis will be generally useful in applications that require understanding of the human visual system.Arkielämän kannalta tärkeät visuaaliset objektit kuten ihmiset, ohikiitävät autot ja kenties kissat, ovat harvoin pistemäisiä, mutta sen sijaan voivat peittää laajankin alueen näkökentästä. Näköaistinsolut prosessoivat kuvainformaatiota erittäin pieneltä näkökentän alueelta ja näköjärjestelmän tulee jollain tavoin yhdistää nämä paikalliset signaalit. Vaikka näköaivokuoren myöhäisten alueiden merkitys spatiaalisesti laajojen objektien havaitsemisessa onkin merkittävä, nykytietämyksen valossa on kiistatonta että myös varhaisten näköaivokuorten hermosolut integroivat spatiaalista kontekstia laajalta näkökentän alueelta. Tässä väitöskirjassa tutkitaan konteksti-integraation taustalla olevien mekanismien spatiaalista rakennetta varhaisessa näköjärjestelmässä. Väitöskirjan ensimmäisessä osatyössä osoitettiin että konteksti-integraatiota yksittäisissä hermosoluissa kuvaavat kahden antagonistisen Gaussilaisen mallit ovat melko hyviä kuvauksia konteksti-integraatiomekanismien spatiaalisesta rakenteesta myös ihmisen näköjärjestelmässä. Ensimmäisessä osatyössä kehitettiin menetelmä joka mahdollistaa havainto- ja aivokuvantamismittausten uudenlaisen yhdistämisen. Tätä menetelmää sovellettiin toisessa osatyössä, jonka päätulos oli konteksti-integraation riippuvuus ärsykkeen koosta näkökentässä sen sijaan että se olisi sidoksissa ärsykkeen edustuksen kokoon aivokuorella. Kolmannessa osatyössä osoitettiin, että kontekstia integroidaan huomattavan laajalta alueelta ja että spatiaalisesti etäinen konteksti saattaa toisinaan vahvistaa näköjärjestelmän kontrastivastetta. Neljäs tutkimus osoitti, että konteksti-integraation valikoivuus orientaatiolle riippuu etäisyydestä niin ihmisen näköhavainnoissa kuin makaki-apinan ensimmäisen näköaivokuoren soluissakin. Tämän väitöskirjan tuloksia voidaan hyödyntää sovelluksissa joissa tarvitaan tietoa ihmisen näköjärjestelmän toiminnasta

Perceptual learning of binocular interactions.

This dissertation focuses on the mechanisms and implications of perceptual learning of binocular interactions. Perceptual learning is an important means of adapting to the changing environment, demonstrating the possibility of neural plasticity in adults and providing a powerful approach to investigate dynamic processes in the mature perceptual system. Most studies on perceptual learning have focused on learning mechanisms that target excitatory circuits. However, we recognize that the inhibitory circuits also play a critical role in cortical plasticity, as shown by growing evidence from neurophysiological studies, and that the inhibitory connection is more dynamic than the excitatory connection in adult visual cortex. Thus, our goal is to design a psychophysical method that exploits the contribution of the inhibitory circuits to perceptual learning. This in turn helps us to implement more efficient learning paradigms for visual training. Our study capitalizes on properties of the binocular visual system, a good system for exploring both excitatory and inhibitory mechanisms. We first measured local Sensory Eye Dominance (SED) and showed that excessive SED can impede stereopsis ability. To reduce SED, a typical perceptual training paradigm (Push-only protocol) would only stimulate the weak eye to target the excitatory network. In contrast, we designed a novel Push-Pull training protocol to target both the excitatory and inhibitory networks. By presenting binocular rivalry stimuli to both eyes, the push-pull protocol can excite the visual pathway of the weak eye (push), while inhibiting the visual pathway of the strong eye (pull). We found that the push-pull training protocol, mainly affecting the early visual processes, is more effective than the push-only protocol in reducing SED and enhancing stereoacuity, even beyond the focus of top-down attention through a stimulus-driven mechanism. We further demonstrated that the perceptual learning induced by the push-pull protocol involves both feature-based and boundary-based processes, and that the learning effect can be generalized to other stimulus dimensions within early feature channels. Therefore, our psychophysical study demonstrates the important role of inhibitory synaptic circuits in neural plasticity of the adult brain, and that our push-pull training protocol can be a more effective clinical training paradigm to treat amblyopia

Colour and spatial pattern discrimination in human vision

Imperial Users onl

Early cross-modal interactions and adult human visual cortical plasticity revealed by binocular rivalry

In this research binocular rivalry is used as a tool to investigate different aspects of visual and multisensory perception. Several experiments presented here demonstrated that touch specifically interacts with vision during binocular rivalry and that the interaction likely occurs at early stages of visual processing, probably V1 or V2. Another line of research also presented here demonstrated that human adult visual cortex retains an unexpected high degree of experience-dependent plasticity by showing that a brief period of monocular deprivation produced important perceptual consequences on the dynamics of binocular rivalry, reflecting a homeostatic plasticity. In summary, this work shows that binocular rivalry is a powerful tool to investigate different aspects of visual perception and can be used to reveal unexpected properties of early visual cortex

Organisation of audio-visual three-dimensional space

Le terme stéréopsie renvoie à la sensation de profondeur qui est perçue lorsqu une scène est vue de manière binoculaire. Le système visuel s appuie sur les disparités horizontales entre les images projetées sur les yeux gauche et droit pour calculer une carte des différentes profondeurs présentes dans la scène visuelle. Il est communément admis que le système stéréoscopique est encapsulé et fortement contraint par les connexions neuronales qui s étendent des aires visuelles primaires (V1/V2) aux aires intégratives des voies dorsales et ventrales (V3, cortex temporal inférieur, MT). A travers quatre projets expérimentaux, nous avons étudié comment le système visuel utilise la disparité binoculaire pour calculer la profondeur des objets. Nous avons montré que le traitement de la disparité binoculaire peut être fortement influencé par d autres sources d information telles que l occlusion binoculaire ou le son. Plus précisément, nos résultats expérimentaux suggèrent que : (1) La stéréo de da Vinci est résolue par un mécanisme qui intègre des processus de stéréo classiques (double fusion), des contraintes géométriques (les objets monoculaires sont nécessairement cachés à un œil, par conséquent ils sont situés derrière le plan de l objet caché) et des connaissances à priori (une préférence pour les faibles disparités). (2) Le traitement du mouvement en profondeur peut être influencé par une information auditive : un son temporellement corrélé avec une cible définie par le mouvement stéréo peut améliorer significativement la recherche visuelle. Les détecteurs de mouvement stéréo sont optimalement adaptés pour détecter le mouvement 3D mais peu adaptés pour traiter le mouvement 2D. (3) Grouper la disparité binoculaire avec un signal auditif dans une dimension orthogonale (hauteur tonale) peut améliorer l acuité stéréo d approximativement 30%Stereopsis refers the perception of depth that arises when a scene is viewed binocularly. The visual system relies on the horizontal disparities between the images from the left and right eyes to compute a map of the different depth values present in the scene. It is usually thought that the stereoscopic system is encapsulated and highly constrained by the wiring of neurons from the primary visual areas (V1/V2) to higher integrative areas in the ventral and dorsal streams (V3, inferior temporal cortex, MT). Throughout four distinct experimental projects, we investigated how the visual system makes use of binocular disparity to compute the depth of objects. In summary, we show that the processing of binocular disparity can be substantially influenced by other types of information such as binocular occlusion or sound. In more details, our experimental results suggest that: (1) da Vinci stereopsis is solved by a mechanism that integrates classic stereoscopic processes (double fusion), geometrical constraints (monocular objects are necessarily hidden to one eye, therefore they are located behind the plane of the occluder) and prior information (a preference for small disparities). (2) The processing of motion-in-depth can be influenced by auditory information: a sound that is temporally correlated with a stereomotion defined target can substantially improve visual search. Stereomotion detectors are optimally suited to track 3D motion but poorly suited to process 2D motion. (3) Grouping binocular disparity with an orthogonal auditory signal (pitch) can increase stereoacuity by approximately 30%PARIS5-Bibliotheque electronique (751069902) / SudocSudocFranceF