Field-specific deficits in visual imagery following hemianopia due to unilateral occipital infarcts.

Patients with stable, homonymous hemianopia due to unilateral occipital infarcts and control subjects performed a task in which they judged whether or not an arrow was pointing at one of the dots in a pattern of dots they had recently seen in free vision, but was no longer visible. This task, as shown in prior studies as well as in the present one, involves the use of visual imagery. The patients made more errors when the arrow pointed to the side ipsilateral to their hemianopia than they did when the arrow pointed to the side contralateral to their hemianopia. The patients' performance in control tasks indicated that this impairment was not due to deficits in several non-imaginal processes required to perform the imagery task, namely scanning the dots and perceiving their spatial positions, memory for their position and encoding arrow direction. These findings support the view that visual imagery involves topographically organized visual areas of the occipital lobe.