Simulating simultanagnosia: spatially constricted vision mimics local capture and the global processing deficit.

Patients with simultanagnosia, which is a component of Bálint syndrome, have a restricted spatial window of visual attention and cannot see more than one object at a time. As a result, these patients see the world in a piecemeal fashion, seeing the local components of objects or scenes at the expense of the global picture. To directly test the relationship between the restriction of the attentional window in simultanagnosia and patients' difficulty with global-level processing, we used a gaze-contingent display to create a literal restriction of vision for healthy participants while they performed a global/local identification task. Participants in this viewing condition were instructed to identify the global and local aspects of hierarchical letter stimuli of different sizes and densities. They performed well at the local identification task, and their patterns of inaccuracies for the global level task were highly similar to the pattern of inaccuracies typically seen with simultanagnosic patients. This suggests that a restricted spatial area of visual processing, combined with normal limits to visual processing, can lead to difficulties with global-level perception.