Functional contributions of the dorsal pathway to shape perception: Evidence from intracranial recording
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Although the dorsal visual pathway is traditionally associated with visuospatial processing to enable action, accumulating evidence indicates that dorsal visual areas also contribute to object perception (Freud et al., 2017). In particular, recent fMRI data suggest that the dorsal pathway contributes to shape perception by computing the spatial arrangement of object parts – a descriptor of global form (Ayzenberg & Behrmann, 2021). However, a full understanding of these computations is limited by the spatial and temporal resolution of fMRI. Here, we leverage the superior spatial and temporal resolution of stereotactic electroencephalography (sEEG), a technique that allows for direct measurement of neural activity, in a pediatric patient with 18 electrode implantations implanted across bilateral parietal cortex (256 channels). To assess whether dorsal regions display sensitivity to the spatial arrangement of object parts, the patient viewed displays wherein the spatial arrangement of object parts varied while holding the features constant or wherein the features of the parts changed while holding the spatial arrangement constant. Consistent with fMRI findings, multiple dorsal channels responded more to the spatial arrangement of parts than to the features of the parts. This finding provides converging evidence, with much finer granularity that dorsal visual regions compute representations that are crucial for shape perception, namely a representation of the spatial arrangement of object parts. Future analyses will build on these findings to test whether, for example, there are hemispheric differences in these representations and whether the global shape of object categories (e.g. guitars independent of specific type of guitar) can be decoded from these regions. Moreover, we will leverage the temporal resolution of sEEG to examine the time course of object processing in dorsal cortex. Together, these findings improve our understanding of functional specificity in visual regions and suggest an important role for dorsal cortex in facilitating object recognition.Keywords:
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Abstract The potential role of visual processing deficits in reading difficulty was brought to public attention by claims that a large proportion of children with dyslexia suffer from a perceptual dysfunction currently referred to as Meares–Irlen syndrome (MISViS). A previous study showing that visual perceptual measures involving visual memory and discrimination predict independent variance in reading achievement [ J. Learn. Disabil. 28 (1995) 216] provides a basis to examine their relationships with the diagnostic criteria of MISViS. This study examined these visual processing characteristics in 36 eight‐ to ten‐year‐old children, half of whom were experiencing reading difficulty. Children were assessed for MISViS by Irlen screeners; approximately half of the participants in each group were positively identified. Concurrent performance on standardized visual processing tests showed that while a positive diagnosis of MISViS is not indicative of reading ability, nor in particular of a visual‐processing deficit subtype identified by Watson and Willows [ J. Learn. Disabil. 28 (1995) 216], MISViS can indicate visual processing difficulties potentially related to visual attention inefficiency.
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Of the nonpathological general population, 0.5% experience one or more visual hallucinations on a regular basis without meeting the criteria for clinical psychosis. We investigated the relationship between a proneness to visual hallucinations in 'normal' individuals and early visual event-related potentials during the perception of faces, Mooney faces and scrambled Mooney faces. Findings indicated that individuals prone to visual hallucinations displayed significantly reduced early event-related potential components (P1, P2, but not N170) over parieto-temporal regions. These findings support previous suggestions that individuals who experience visual hallucinations exhibit abnormal early visual processing resulting from degraded visual input, in this case owing to disruption of low level visual processes.
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Evidence reveals that visual processing speed decreases with age. The Motor-Free Visual Perception Test- Third Edition (MVPT-3) has an age-normed Response Time Index that measures visual processing speed. In 2015, a new version, Motor-Free Visual Perception Test- Fourth Edition (MVPT-4), was published. The new MVPT-4 does not yet demonstrate its utility in measuring visual processing speed. The purpose of this study was to explore if differences in visual processing speed between younger adults ages 20-35 years and older adults ages 70 years and older could be detected using the new MVPT-4. Results revealed a significant difference between older and younger adults’ time to complete the MVPT-4 (p <.05). This pilot study demonstrated that the MVPT-4 may be able to detect age-related changes in visual processing speed and therefore, a possible clinical tool for occupational therapists.
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Visual processing starts at the retina of the eye, and signals are then transferred primarily to the visual cortex and the tectum. In the retina, multiple neural networks encode different aspects of visual input, such as color and motion. Subsequently, multiple neural streams in parallel convey unique aspects of visual information to cortical and subcortical regions. Bipolar cells, which are the second order neurons of the retina, separate visual signals evoked by light and dark contrasts and encode them to ON and OFF pathways, respectively. The interplay between ON and OFF neural signals is the foundation for visual processing for object contrast which underlies higher order stimulus processing. ON and OFF pathways have been classically thought to signal in a mirror-symmetric manner. However, while these two pathways contribute synergistically to visual perception in some instances, they have pronounced asymmetries suggesting independent operation in other cases. In this review, we summarize the role of the ON-OFF dichotomy in visual signaling, aiming to contribute to the understanding of visual recognition.
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This chapter starts out by contrasting the static image-processing tradition in vision research to the moving-observer tradition in ecological psychology. As visual neuroscience and computer vision began to test awake behaving monkeys and robots, respectively, instead of motionless observers, some of the most vexing problems of image processing melted away. Feedback projections from higher visual brain areas down to lower visual brain areas appear to exert a goal-oriented tuning of the perceptual process. Moreover, oculomotor processes are shown to play a role in perceptual decisions, suggesting a blurring of the lines between visual perception and visual cognition and visuomotor processes. The chapter focuses especially on visual search processes and simulations of linear increases in reaction time resulting from a parallel-processing model.
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Abstract Visual perception and awareness have strict limitations. We suggest that one source of these limitations is the representational architecture of the visual system. Under this view, the extent to which items activate the same neural channels constrains the amount of information that can be processed by the visual system and ultimately reach awareness. Here, we measured how well stimuli from different categories (e.g., faces and cars) blocked one another from reaching awareness using two distinct paradigms that render stimuli invisible: visual masking and continuous flash suppression. Next, we used fMRI to measure the similarity of the neural responses elicited by these categories across the entire visual hierarchy. Overall, we found strong brain–behavior correlations within the ventral pathway, weaker correlations in the dorsal pathway, and no correlations in early visual cortex (V1–V3). These results suggest that the organization of higher level visual cortex constrains visual awareness and the overall processing capacity of visual cognition.
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Older adults are at a significantly increased risk of being involved in motor vehicle accidents. Evidence reveals that visual processing speed decreases with age, which may impact driving. The Motor-Free Visual Perception Test- Third Edition (MVPT-3) is used as a pre-driving assessment and has an age-normed Response Time Index that measures visual processing speed. In 2015, a new version, the new Motor-Free Visual Perception Test- Fourth Edition (MVPT-4), was published. The new MVPT-4 does not yet demonstrate its utility in measuring visual processing speed. The purpose of this study was to explore if differences in visual processing speed between younger adults ages 20-35 years and older adults ages 70 years and older could be detected using the new MVPT-4. Results revealed a significant difference between older and younger adults’ time to complete the MVPT-4 (p
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