The lateral occipital complex subserves the perceptual persistence of motion-defined groupings.

How are the bits and pieces of retinal information assembled and integrated to form the coherent objects that we see? One long-established principle is that elements that move as a group are linked together. For instance a fragmented line-drawing of an object, placed on a background of randomly distributed short lines, can be impossible to see. But if the object moves relative to the background, its shape is instantly recognized. Even after the motion stops, the percept of the object persists briefly before it fades into the background of random lines. Where in the brain does the percept of the object persist? Using functional brain imaging, we found that such moving line-drawings activated both motion-sensitive areas (medial temporal complex, MT+) and object-sensitive areas (lateral occipital complex, LOC). However, after the motion stopped only the LOC maintained its activity while the percept endured. Evidently a percept assembled by motion-sensitive areas like MT+ can be stored, at least briefly, in the LOC

Altered visual perception near the hands: a critical review of attentional and neurophysiological models

Visual perception changes as a function of hand proximity. While various theoretical accounts have been offered for this alteration (attentional prioritisation, bimodal cell involvement, detailed evaluation, and magnocellular neuron input enhancement), the current literature lacks consensus on these mechanisms. The purpose of this review, therefore, is to critically review the existing body of literature in light of these distinct theoretical accounts. We find that a growing number of results support the magnocellular (M-cell) enhancement account, and are difficult to reconcile with general attention-based explanations. Despite this key theoretical development in the field, there has been some ambiguity with interpretations offered in recent papers, for example, equating the existing attentional and M-cell based explanations, when in fact they make contrasting predictions. We therefore highlight the differential predictions arising from the distinct theoretical accounts. Importantly, however, we also offer novel perspectives that synthesises the role of attention and neurophysiological mechanisms in understanding altered visual perception near the hands. We envisage that this theoretical development will ensure that the field can progress from documenting behavioural differences, to a consensus on the underlying visual and neurophysiological mechanisms.This research was supported by an Australian Research Council (ARC) Discovery Early Career Research Award (DE140101734) awarded to S.C.G., ARC Discovery Project (DP110104553) awarded to M.E, a Natural Sciences and Engineering Research Council of Canada (NSERC) Discovery Grants awarded S.F. and J.P

Revisiting unilateral neglect

Abstract Unilateral neglect, a neurological disorder in which patients fail to detect or respond to contralesional stimuli, has long been considered a failure of attentional orienting mechanisms. This review provides a selective overview of the prominent biases in spatial orienting and exploratory motor behaviour observed in these patients before considering the impact of other factors on the presentation of the disorder and how those factors might inform current neurological models of neglect. In the latter part of the review we intend to suggest that neglect is likely to be a combination of distinct but interacting impairments including biases in attentional orienting, exploratory motor behaviours and a deficit of spatial working memory. That is, we suggest that the cardinal symptom of neglect -a loss of awareness for contralesional stimuli and events -arises as a result of a combination of these impairments rather than being associated solely with the more dramatic and immediately evident biases in spatial attention

Visual Search Elicits the Electrophysiological Marker of Visual Working Memory

Background: Although limited in capacity, visual working memory (VWM) plays an important role in many aspects of visually-guided behavior. Recent experiments have demonstrated an electrophysiological marker of VWM encoding and maintenance, the contralateral delay activity (CDA), which has been shown in multiple tasks that have both explicit and implicit memory demands. Here, we investigate whether the CDA is evident during visual search, a thoroughly-researched task that is a hallmark of visual attention but has no explicit memory requirements. Methodology/Principal Findings: The results demonstrate that the CDA is present during a lateralized search task, and that it is similar in amplitude to the CDA observed in a change-detection task, but peaks slightly later. The changes in CDA amplitude during search were strongly correlated with VWM capacity, as well as with search efficiency. These results were paralleled by behavioral findings showing a strong correlation between VWM capacity and search efficiency. Conclusions/Significance: We conclude that the activity observed during visual search was generated by the same neura

Pop-out and pop-in: Visual working memory advantages for unique items

Attentional control is thought to play a critical role in determining the amount of information that can be stored and retrieved from visual working memory (VWM). We tested whether and how task-irrelevant feature-based salience, known to affect the control of visual attention, affects VWM performance. Our results show that features of a task-irrelevant color singleton are more likely to be recalled from VWM than non-singleton items and that this increased memorability comes at a cost to the other items in the display. Furthermore, the singleton effect in VWM was negatively correlated with an individual’s baseline VWM capacity. Taken together, these results suggest that individual differences in VWM storage capacity may be partially attributable to the ability to ignore differences in task-irrelevant physical salience

Neural representation of geometry and surface properties in object and scene perception

Multiple cortical regions are crucial for perceiving the visual world, yet the processes shaping representations in these regions are unclear. To address this issue, we must elucidate how perceptual features shape representations of the environment. Here, we explore how the weighting of different visual features affects neural representations of objects and scenes, focusing on the scene-selective parahippocampal place area (PPA), but additionally including the retrosplenial complex (RSC), occipital place area (OPA), lateral occipital (LO) area, fusiform face area (FFA) and occipital face area (OFA). Across three experiments, we examined functional magnetic resonance imaging (fMRI) activity while human observers viewed scenes and objects that varied in geometry (shape/layout) and surface properties (texture/material). Interestingly, we found equal sensitivity in the PPA for these properties within a scene, revealing that spatial-selectivity alone does not drive activation within this cortical region. We also observed sensitivity to object texture in PPA, but not to the same degree as scene texture, and representations in PPA varied when objects were placed within scenes. We conclude that PPA may process surface properties in a domain-specific manner, and that the processing of scene texture and geometry is equally-weighted in PPA and may be mediated by similar underlying neuronal mechanisms

The impact of multisensory integration deficits on speech perception in children with autism spectrum disorders.

Speech perception is an inherently multisensory process. When having a face-to-face conversation, a listener not only hears what a speaker is saying, but also sees the articulatory gestures that accompany those sounds. Speech signals in visual and auditory modalities provide complementary information to the listener (Kavanagh and Mattingly, 1974), and when both are perceived in unison, behavioral gains in in speech perception are observed (Sumby and Pollack, 1954). Notably, this benefit is accentuated when speech is perceived in a noisy environment (Sumby and Pollack, 1954). To achieve a behavioral gain from multisensory processing of speech, however, the auditory and visual signals must be perceptually bound into a single, unified percept. The most commonly cited effect that demonstrates perceptual binding in audiovisual speech perception is the McGurk effect (McGurk and MacDonald, 1976), where a listener hears a speaker utter the syllable “ba,” and sees the speaker utter the syllable “ga.” When these two speech signals are perceptually bound, the listener perceives the speaker as having said “da” or “tha,” syllables that are not contained in either of the unisensory signals, resulting in a perceptual binding, or integration, of the speech signals (Calvert and Thesen, 2004)

Transient Perceptual Neglect: Visual Working Memory Load Affects Conscious Object Processing

Abstract ■ Visual working memory ( VWM) is a capacity-limited cognitive resource that plays an important role in complex cognitive behaviors. Recent studies indicate that regions subserving VWM may play a role in the perception and recognition of visual objects, suggesting that conscious object perception may depend on the same cognitive and neural architecture that supports the maintenance of visual object information. In the present study, we examined this question by testing object processing under a concurrent VWM load. Under a high VWM load, recognition was impaired for objects presented in the left visual field, in particular when two objects were presented simultaneously. Multivariate fMRI revealed that two independent but partially overlapping networks of brain regions contribute to object recognition. The first network consisted of regions involved in VWM encoding and maintenance. Importantly, these regions were also sensitive to object load. The second network comprised regions of the ventral temporal lobes traditionally associated with object recognition. Importantly, activation in both networks predicted object recognition performance. These results indicate that information processing in regions that mediate VWM may be critical to conscious visual perception. Moreover, the observation of a hemifield asymmetry in object recognition performance has important theoretical and clinical significance for the study of visual neglect.

Transient perceptual neglect: visual working memory load affects conscious object processing

Visual working memory (VWM) is a capacity-limited cognitive resource that plays an important role in complex cognitive behaviors. Recent studies indicate that regions subserving VWM may play a role in the perception and recognition of visual objects, suggesting that conscious object perception may depend on the same cognitive and neural architecture that supports the maintenance of visual object information. In the present study, we examined this question by testing object processing under a concurrent VWM load. Under a high VWM load, recognition was impaired for objects presented in the left visual field, in particular when two objects were presented simultaneously. Multivariate fMRI revealed that two independent but partially overlapping networks of brain regions contribute to object recognition. The first network consisted of regions involved in VWM encoding and maintenance. Importantly, these regions were also sensitive to object load. The second network comprised regions of the ventral temporal lobes traditionally associated with object recognition. Importantly, activation in both networks predicted object recognition performance. These results indicate that information processing in regions that mediate VWM may be critical to conscious visual perception. Moreover, the observation of a hemifield asymmetry in object recognition performance has important theoretical and clinical significance for the study of visual neglect