Perception of global gestalt by temporal integration in simultanagnosia.

ABSTRACT

Patients with bilateral parieto-occipital brain damage may show intact processing of individual objects, while their perception of multiple objects is disturbed at the same time. The deficit is termed 'simultanagnosia' and has been discussed in the context of restricted visual working memory and impaired visuo-spatial attention. Recent observations indicated that the recognition of global shapes can be modulated by the spatial distance between individual objects in patients with simultanagnosia and thus is not an all-or-nothing phenomenon depending on spatial continuity. However, grouping mechanisms not only require the spatial integration of visual information, but also involve integration processes over time. The present study investigated motion-defined integration mechanisms in two patients with simultanagnosia. We applied hierarchical organized stimuli of global objects that consisted of coherently moving dots ('shape-from-motion'). In addition, we tested the patients' ability to recognize biological motion by presenting characteristic human movements ('point-light-walker'). The data revealed largely preserved perception of biological motion, while the perception of motion-defined shapes was impaired. Our findings suggest separate mechanisms underlying the recognition of biological motion and shapes defined by coherently moving dots. They thus argue against a restriction in the overall capacity of visual working memory over time as a general explanation for the impaired global shape recognition in patients with simultanagnosia.