Dissociation between contour-based and Texture-based Shape Perception: a single case study.

A single case study of a patient suffering from a temporo-parietal lesion is presented. He was impaired at recognizing shape on the basis of texture information, whereas shape recognition on the basis of contours seemed comparatively preserved. To investigate the impaired level in texture processing, we used two alternative forced-choice tasks to test figure-ground segregation based on textural differences in contrasting modalities (tactile vs. visual) and viewing conditions (static vs. apparently moving stimuli). The results showed that the deficit was specific to visual stimuli (both static and dynamic). Moreover, this deficit did not occur with local texture analysis, but was always present in global texture segregation tasks. This suggests that contour analysis and texture segregation are separable operations in shape processing. The patient's impairments are attributed to an inability to activate global processing of stimuli defined by texture but not by contours.