Abstract: Foreword Human Visual Processing Visual Factors in Cognitive Dysfunction and Enhancement in Alzheimer's Disease by Alice Cronin-Golomb and Grover C. Gilmore Exploring Visual Perception Abilities in Individuals with Intellectual Disabilities: Assessment and Implications by Stephen Oross III and Charles B. Woods Enhancing Performances of Individuals with Mental Retardation: Manipulations of Visual Structure by Michael T. Carlin, Sal A. Soraci, and Christina Strawbridge Stimulus Overselectivity and Observing Behavior in Individuals with Mental Retardation by William V. Dube, et al. Arousal Modulation of Neonatal Visual Attention: Implications for Development by Judith M. Gardner, Bernard Z. Karmel, and Micharl J. Flory Visual Process Strengths in Down Syndrome: A Case for Reading Instruction? by Robert M. Hodapp and Tran M. Ly Visual Variability Discrimination by Michael E. Young and Edward A. Wasserman Animal Visual Processing The Multiplicity of Visual Search Strategies in Pigeons by Jeffrey S. Katz and Robert G. Cook The Search for Relational Learning in Cebus Apella: A Programmed "Educational" Approach by Romariz da Silva Barros, Olavo de Faria Galvao, and William J. McIlvane Visualism: Philosophical Approaches Visualism in Space by Don Ihde Technology, Transcendence, and Modernity: Marcel and Jaspers by Gregory J. Walters Alterity in Memory by Kimiyo Murata-Soraci

Abstract: Spontaneous cortical activity--ongoing activity in the absence of intentional sensory input--has been studied extensively, using methods ranging from EEG (electroencephalography), through voltage sensitive dye imaging, down to recordings from single neurons. Ongoing cortical activity has been shown to play a critical role in development, and must also be essential for processing sensory perception, because it modulates stimulus-evoked activity, and is correlated with behaviour. Yet its role in the processing of external information and its relationship to internal representations of sensory attributes remains unknown. Using voltage sensitive dye imaging, we previously established a close link between ongoing activity in the visual cortex of anaesthetized cats and the spontaneous firing of a single neuron. Here we report that such activity encompasses a set of dynamically switching cortical states, many of which correspond closely to orientation maps. When such an orientation state emerged spontaneously, it spanned several hypercolumns and was often followed by a state corresponding to a proximal orientation. We suggest that dynamically switching cortical states could represent the brain's internal context, and therefore reflect or influence memory, perception and behaviour.

Abstract: Although the parietal cortex has been implicated in the neural processes underlying visual attention, the nature of its contribution is not well understood. We tracked attention in the monkey and correlated the activity of neurons in the lateral intraparietal area (LIP) with the monkey's attentional performance. The ensemble activity in LIP across the entire visual field describes the spatial and temporal dynamics of a monkey's attention. Activity subtending a single location in the visual field describes the attentional priority at that area but does not predict that the monkey will actually attend to or make an eye movement to that location.

Abstract: The subjective experience of perceiving visual stimuli is accompanied by objective neuronal activity patterns such as sustained activity in primary visual area (V1), amplification of perceptual processing, correlation across distant regions, joint parietal, frontal, and cingulate activation, γ-band oscillations, and P300 waveform. We describe a neuronal network model that aims at explaining how those physiological parameters may cohere with conscious reports. The model proposes that the step of conscious perception, referred to as access awareness, is related to the entry of processed visual stimuli into a global brain state that links distant areas including the prefrontal cortex through reciprocal connections, and thus makes perceptual information reportable by multiple means. We use the model to simulate a classical psychological paradigm: the attentional blink. In addition to reproducing the main objective and subjective features of this paradigm, the model predicts an unique property of nonlinear transition from nonconscious processing to subjective perception. This all-or-none dynamics of conscious perception was verified behaviorally in human subjects.

Abstract: PASSIVE VISION AND ACTIVE VISION 1.1 Introduction 1.2 Passive vision 1.3 Visual attention 1.4 Active vision 1.5 Active vision and vision for action 1.6 Outline of the book BACKGROUND TO ACTIVE VISION 2.1 Introduction 2.2 The inhomogeneity of the visual projections 2.3 Parallel visual pathways 2.4 The oculomotor system 2.5 Saccadic eye movements 2.6 Summary VISUAL SELECTION, COVERT ATTENTION AND EYE MOVEMENTS 3.1 Covert and overt attention 3.2 Covert spatial attention 3.3 The relationship between covert and overt attention 3.4 Speed of attention 3.5 Neurophysiology of attention 3.6 Non-spatial attention 3.7 Active vision and attention 3.8 Summary VISUAL ORIENTING 4.1 Introduction 4.2 What determines the latency of orienting saccades? 4.3 Physiology of saccade initiation 4.4 What determines the landing position of orienting saccades? 4.5 Physiology of the WHERE system 4.6 The Findlay and Walker model 4.7 Development and plasticity VISUAL SAMPLING DURING TEXT READING 5.1 Introduction 5.2 Basic patterns of visual sampling during reading 5.3 Perception during fixations in reading 5.4 Language processing 5.5 Control of fixation duration 5.6 Control of landing position 5.7 Theories of eye control during reading 5.8 Practical aspects of eye control in reading 5.9 Overview VISUAL SEARCH 6.1 Visual search tasks 6.2 Theories of visual search 6.3 The need for eye movements in visual search 6.4 Eye movements in visual search 6.5 Ocular capture in visual search 6.6 Saccades in visual search: scanpaths 6.7 Physiology of visual search 6.8 Summary NATURAL SCENES AND ACTIVITIES 7.1 Introduction 7.2 Analytic studies of scene and object perception 7.3 Dynamic scenes and situations 7.4 Summary HUMAN NEUROPSYCHOLOGY 8.1 Blindsight 8.2 Neglect 8.3 Balint's syndrome and dorsal simultanagnosia 8.4 Frontal lobe damage 8.5 Orienting without eye movements 8.6 Summary SPACE CONSTANCY AND TRANS-SACCADIC INTEGRATION 9.1 The traditional approach: 'compensatory taking into account' 9.2 Trans-saccadic integration 9.3 Resolution of the conflicting results 9.4 Conclusion: The Active Vision Cycle 9.5 Future directions

Abstract: A key function of emotion is the preparation for action. However, organization of successful behavioral strategies depends on efficient stimulus encoding. The present study tested the hypothesis that perceptual encoding in the visual cortex is modulated by the emo- tional significance of visual stimuli. Event-related brain potentials were measured while subjects viewed pleasant, neutral, and unpleas- ant pictures. Early selective encoding of pleasant and unpleasant im- ages was associated with a posterior negativity, indicating primary sources of activation in the visual cortex. The study also replicated previous findings in that affective cues also elicited enlarged late posi- tive potentials, indexing increased stimulus relevance at higher-order stages of stimulus processing. These results support the hypothesis that sensory encoding of affective stimuli is facilitated implicitly by natural selective attention. Thus, the affect system not only modulates motor output (i.e., favoring approach or avoidance dispositions), but already operates at an early level of sensory encoding.

Abstract: Autistic children and typically developing control children were tested on two visual tasks, one involving grouping of small line elements into a global figure and the other involving perception of hu- man activity portrayed in point-light animations. Performance of the two groups was equivalent on the figure task, but autistic children were significantly impaired on the biological motion task. This latter deficit may be related to the impaired social skills characteristic of autism, and we speculate that this deficit may implicate abnormalities in brain areas mediating perception of human movement.

Abstract: Although many neuroimaging studies of visual mental imagery have revealed activation in early visual cortex (Areas 17 or 18), many others have not. The authors review this literature and compare how well 3 models explain the disparate results. Each study was coded 1 or 0, indicating whether activation in early visual cortex was observed, and sets of variables associated with each model were fit to the observed results using logistic regression analysis. Three variables predicted all of the systematic differences in the probability of activation across studies. Two of these variables were identified with a perceptual anticipation theory, and the other was identified with a methodological factors theory. Thus, the variability in the literature is not random.

Abstract: In Seeing and Visualizing, Zenon Pylyshyn argues that seeing is different from thinking and that to see is not, as it may seem intuitively, to create an inner replica of the world. Pylyshyn examines how we see and how we visualize and why the scientific account does not align with the way these processes seem to us "from the inside." In doing so, he addresses issues in vision science, cognitive psychology, philosophy of mind, and cognitive neuroscience. First, Pylyshyn argues that there is a core stage of vision independent from the influence of our prior beliefs and examines how vision can be intelligent and yet essentially knowledge-free. He then proposes that a mechanism within the vision module, called a visual index (or FINST), provides a direct preconceptual connection between parts of visual representations and things in the world, and he presents various experiments that illustrate the operation of this mechanism. He argues that such a deictic reference mechanism is needed to account for many properties of vision, including how mental images attain their apparent spatial character without themselves being laid out in space in our brains. The final section of the book examines the "picture theory" of mental imagery, including recent neuroscience evidence, and asks whether any current evidence speaks to the issue of the format of mental images. This analysis of mental imagery brings together many of the themes raised throughout the book and provides a framework for considering such issues as the distinction between the form and the content of representations, the role of vision in thought, and the relation between behavioral, neuroscientific, and phenomenological evidence regarding mental representations.

Abstract: Cortical-form vision comprises multiple, hierarchically arranged areas with feedforward and feedback interconnections. This complex architecture poses difficulties for attempts to link perceptual phenomena to activity at a particular level of the system. This difficulty has been especially salient in studies of binocular rivalry alternations, where there is seemingly conflicting evidence for a locus in primary visual cortex or alternatively in higher cortical areas devoted to object perception. Here, I use a competitive neural model to demonstrate that the data require at least two hierarchic rivalry stages for their explanation. This model demonstrates that competitive inhibition in the first rivalry stage can be eliminated by using suitable stimulus dynamics, thereby revealing properties of a later stage, a result obtained with both spike-rate and conductance-based model neurons. This result provides a synthesis of competing rivalry theories and suggests that neural competition may be a general characteristic throughout the form-vision hierarchy.

Abstract: The perception of colour is a central component of primate vision. Colour facilitates object perception and recognition, and has an important role in scene segmentation and visual memory. Moreover, it provides an aesthetic component to visual experiences that is fundamental to our perception of the world. Despite the long history of colour vision studies, much has still to be learned about the physiological basis of colour perception. Recent advances in our understanding of the early processing in the retina and thalamus have enabled us to take a fresh look at cortical processing of colour. These studies are beginning to indicate that colour is processed not in isolation, but together with information about luminance and visual form, by the same neural circuits, to achieve a unitary and robust representation of the visual world.

Abstract: We used functional magnetic resonance imaging (fMRI) to measure activity in human early visual cortex (areas V1, V2 and V3) during a challenging contrast-detection task. Subjects attempted to detect the presence of slight contrast increments added to two kinds of background patterns. Behavioral responses were recorded so that the corresponding cortical activity could be grouped into the usual signal detection categories: hits, false alarms, misses and correct rejects. For both kinds of background patterns, the measured cortical activity was retinotopically specific. Hits and false alarms were associated with significantly more cortical activity than were correct rejects and misses. That false alarms evoked more activity than misses indicates that activity in early visual cortex corresponded to the subjects' percepts, rather than to the physically presented stimulus.

Abstract: Visual stimuli are known to influence the perception of auditory stimuli in spatial tasks, giving rise to the ventriloquism effect. These influences can persist in the absence of visual input following a period of exposure to spatially disparate auditory and visual stimuli, a phenomenon termed the ventriloquism aftereffect. It has been speculated that the visual dominance over audition in spatial tasks is due to the superior spatial acuity of vision compared with audition. If that is the case, then the auditory system should dominate visual perception in a manner analogous to the ventriloquism effect and aftereffect if one uses a task in which the auditory system has superior acuity. To test this prediction, the interactions of visual and auditory stimuli were measured in a temporally based task in normal human subjects. The results show that the auditory system has a pronounced influence on visual temporal rate perception. This influence was independent of the spatial location, spectral bandwidth, and intensity of the auditory stimulus. The influence was, however, strongly dependent on the disparity in temporal rate between the two stimulus modalities. Further, aftereffects were observed following approximately 20 min of exposure to temporally disparate auditory and visual stimuli. These results show that the auditory system can strongly influence visual perception and are consistent with the idea that bimodal sensory conflicts are dominated by the sensory system with the greater acuity for the stimulus parameter being discriminated.

Abstract: In natural environments, humans select a subset of visual stimuli by directing their gaze to locations attended. In previous studies it has been found that at fixation points luminance-contrast is higher than average. This led to the hypothesis that luminance-contrast makes a major contribution to a saliency map of visual overt attention, consistent with a computation of stimulus saliency in early visual cortical areas. We re-evaluate this hypothesis by using natural and modified natural images to uncover the causal effects of luminance-contrast to human overt visual attention and: (i) we confirm that when viewing natural images, contrasts are elevated at fixation points. This, however, only holds for low spatial frequencies and in a limited temporal window after stimulus onset; (ii) however, despite this correlation between overt attention and luminance-contrast, moderate modifications of contrast in natural images do not measurably affect the selection of fixation points. Furthermore, strong local reductions of luminance-contrast do not repel but attract fixation; (iii) neither contrast nor contrast modification is correlated to fixation duration; and (iv), even the moderate contrast modifications used fall into the physiologically relevant range, and subjects are well able to detect them in a forced choice paradigm. In summary, no causal contribution of luminance-contrast to a saliency map of human overt attention is detectable. In conjunction with recent results on the relation of contrast sensitivity of neuronal activity to the level in the visual cortical hierarchy, the present study provides evidence that, for natural scenes, saliency is computed not early but late during processing.

Abstract: Previous studies have demonstrated that top-down factors can bias the storage of information in visual working memory. However, relatively little is known about the role that bottom-up stimulus characteristics play in visual working memory storage. In the present study, subjects performed a change detection task in which the to-be-remembered objects were organized in accordance with Gestalt grouping principles. When an attention-capturing cue was presented at the location of one object, other objects that were perceptually grouped with the cued object were more likely to be stored in working memory than were objects that were not grouped with the cued object. Thus, objects that are grouped together tend to be stored together, indicating that bottom-up perceptual organization influences the storage of information in visual working memory.

Abstract: Studies using fMRI have demonstrated that visual stimuli activate auditory cortex in deaf subjects. Given the low temporal resolution of fMRI, it is uncertain whether this activation is associated with initial stimulus processing. Here, we used MEG in deaf and hearing subjects to evaluate whether auditory cortex, devoid of its normal input, comes to serve the visual modality early in the course of stimulus processing. In line with previous findings, visual activity was observed in the auditory cortex of deaf, but not hearing, subjects. This activity occurred within 100-400 ms of stimulus presentation and was primarily over the right hemisphere. These results add to the mounting evidence that removal of one sensory modality in humans leads to neural reorganization of the remaining modalities.

Abstract: Visually guided grasping movements require a rapid transformation of visual representations into object-specific motor programs. Here we report that graspable objects may facilitate these visuomotor transformations by automatically grabbing visual spatial attention. Human subjects viewed two taskirrelevant objects—one was a ‘tool’, the other a ‘non-tool’—while waiting for a target to be presented in one of the two object locations. Using event-related potentials (ERPs), we found that spatial attention was systematically drawn to tools in the right and lower visual fields, the hemifields that are dominant for visuomotor processing. Using event-related fMRI, we confirmed that tools grabbed spatial attention only when they also activated dorsal regions of premotor and prefrontal cortices, regions associated with visually guided actions and their planning. Although it is widely accepted that visual sensory gain aids perception, our results suggest that it may also have consequences for object-directed actions.