Abstract
Purpose: Although the perception of biological motion mimicking human walking is compelling and seems spontaneous and effortless, it actually demands attention (Cavanagh, Labianca, & Thornton, 2001). Since unilateral parietal patients show deficits in perceiving attention-based apparent motion (Battelli et al, 2002), we explored whether these patients would also be impaired in the perception of biological motion. Method: Three unilateral parietal patients were tested in three experiments. One low-level form-from-motion and two visual search tasks were used. In the first visual search experiment subjects searched for a walker facing opposite to the distractors walker, while in the second they searched for a normal walker among jumbled ones. In both search tasks set size varied between one and four items randomly across trials. Accuracy and reaction times were measured. Results: All patients could easily perform the classical low-level motion task at normal levels. However, they were severely impaired in the visual search tasks using biological motion sequences showing elevated error rates and reaction time compared to normals. Furthermore the left parietal patient performed much worse than the right parietals. Conclusions: Since our patients' low-level motion mechanisms are preserved, we suggest that the perception of biological motion requires high-level analysis of dynamic patterns, an attention-based process that is impaired in parietal lobe patients.
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