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Marina Pavlovskaya, Yoram Bonneh, Shaul Hochstein, Nachum Soroker; Occasional awareness of a tree with no forest: Deriving PPC perceptual role from a simultanagnosia case study . Journal of Vision 2016;16(12):618. doi: 10.1167/16.12.618.
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© 2017 Association for Research in Vision and Ophthalmology.
Background: Patients with Balint syndrome following bilateral parietal damage are typically described as being unable to perceive multiple objects simultaneously, preventing them from understanding the visual scene despite correct identification of individual visual objects (simultanagnosia). We report observations with DP, a patient with a rare stroke-related pattern of damage affecting the right and left posterior parietal cortex (PPC), shedding new light on simultanagnosia and the role of PPC in conscious perception. Results: (1) DP experienced fading or disappearance of salient objects or object parts, such as face parts, or even a single patch on a blank screen, reporting alternating onsets and offsets every few seconds. He also reported anti-correlated disappearance of competing objects such as orthogonal bars. (2) DP had a surprisingly intact ability to identify very small digits or color patches, when centrally presented, but this was dramatically degraded when spatially crowded with flanking patterns. (3) He had a severe deficit in reporting relative positions of objects or pointing to marked locations on a touch screen. (4) Nevertheless, both in Gestalt grouping and in size-averaging tasks, DP seemed to be grouping arrays, some of which were invisible to him. Conclusions: These findings, and especially the dynamic alternating perception and fading of isolated patches or large fragments of the visual scene, are not consistent with common single-object perception descriptions of this syndrome, and theories stressing a global/focal imbalance. We propose that PPC serves as a short-term data-holding mechanism for spatially coded information by which contextual factors modulate perception-declaration and perception-action links. Bilateral PPC damage causes simultanagnosia due to failed maintenance of visual information in spatio-temporal working memory.
Meeting abstract presented at VSS 2016
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