Perception of biological motion in parietal patients.

Three unilateral parietal patients were tested on their perception of biological motion, a special case of form-from-motion. Two patients had the lesion in the right, and one in the left parietal area. All patients could easily perform a classical form-from-motion task [Neuron 32 (2001) 985], but they were severely impaired in a visual search task using biological motion sequences. In particular, the left parietal patient showed a more severe loss. He was unable to identify even a single item. Overall our patients seemed to perform differently from the classical motion-blind patients described in the literature [Visual Cognition 3 (1996) 363; Eur. J. Neurol. 9 (2002) 463; Visual Neurosci. 5 (1990) 353] whose lesions included the visual cortical area V5. Since our patients' low-level motion mechanisms are preserved, we suggest that the perception of biological motion relies on a high-level description of dynamic patterns [Cognition 80 (2001) 47], a mechanism that is impaired in parietal lobe patients. We discuss our results at the light of the recent theories suggesting that biological motion is performed by visual associative areas outside the classical motion pathways and that it is an active process dependent on attentional resources [Cognition 80 (2001) 47].