The attentional fields of visual search in simultanagnosia and healthy individuals: How object and space attention interact

Abstract

Simultanagnosia is a deficit in which patients are unable to perceive multiple objects simultaneously. To date, it remains disputed whether this deficit results from disrupted object or space perception. We asked both healthy participants as well as a patient with simultanagnosia to perform different visual search tasks (both pop-out and serial) of variable difficulty using different gaze-contingent visible window sizes. This allowed us to determine the size of the attentional span used for each visual search task; only visible windows that were smaller than the specific attentional span used for the task resulted in a cost in reaction times to find the search target. To determine whether this attentional span varied according to object or space, we also modulated the number of objects (target and distracters). For healthy participants, we found that each visual search task was performed with a specific attentional span depending on the difficulty of visual object processing but not on the number of objects falling within this space. For the patient with simultanagnosia, we found a reduced attentional span compared to controls but only for search tasks with objects that were made up of separable features. This did not vary according to the number of objects. Thus, we conclude that bilateral damage to the superior parietal lobule (SPL) impairs the spatial integration of separable features (within-object processing), shrinking the attentional span within which a target can be detected, but causing no deficit in processing multiple objects per se.

Meeting abstract presented at VSS 2016