Perception of ambiguous figures after focal brain lesions.
Forty patients with unilateral frontal or posterior brain damage and 20 normal control subjects were tested on an ambiguous figures task (AFT). For each figure they were asked to recognize both ambiguous images. Subjects failing to recognize the second aspect of an ambiguous figure were prompted with the name of the image not yet perceived. The Wisconsin Card Sorting Test (WCST) was also administered to all subjects. Frontal patients exhibited greater difficulty in shifting from one aspect of an ambiguous figure to the other than did patients with more posterior lesions and control subjects. In addition, frontal-posterior and control differences were highly significant for number of prompts given. For the frontal patients, significant correlations were found between the number of prompts on the AFT and the number of perseverative errors on the WCST. Poor performance on the AFT can be considered as a "frontal lobe sign" of perceptual persevation.