Perception of global gestalt by temporal integration in simultanagnosia

The coherent processing of our environment requires the integration of local elements into a global gestalt. Patients with bilateral parieto-occipital brain damage show intact processing of individual objects, while their simultaneous perception of multiple objects at the same time is disturbed. This 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 perception of global gestalt 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 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-like Walker'). The data revealed largely preserved perception of biological motion, while the perception of motion defined shapes was impaired. These findings suggest separate mechanisms underlying the recognition of biological motion and shape-from-motion. They thus argue against a restriction in the overall capacity of visual working memory over time as a general explanation for the impaired global gestalt perception in patients with simultanagnosia.