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Lorella Battelli, Bradford Mahon, Ian Thornton; Incidental processing of biological motion in parietal patients. Journal of Vision 2007;7(9):489. doi: 10.1167/7.9.489.
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Purpose: It is known that biological motion processing can proceed in a passive, bottom-up manner. Using an incidental processing paradigm, Thornton and Vuong (2004) recently demonstrated that observers respond more quickly to target figures walking in the same direction as to-be-ignored flankers (dynamic congruency effect), indicating that the to-be-ignored items still exert an influence on behavior. Is such bottom-up processing sufficient for explicit awareness? Here we report results from two parietal patients who show a total inability to explicitly recognize isolated biological motion figures, despite intact low-level motion perception. Will these patients still show a flanker effect? Method: Two parietal patients were tested on flanker tasks involving a) biological motion (BM) stimuli and b) complex non-biological rotating (CR) patterns. In both tasks central target figures were presented simultaneously with two other items (flankers) presented on either side of the target. Response dimensions were left/right for BM and clockwise/counter-clockwise for CR stimuli respectively. Flankers moved in either the same direction as the target (congruent) or in the opposite direction (incongruent). Subjects were instructed to ignore the flankers. Results: Both patients performed the CR task at normal levels. In contrast, performance was severely impaired in the BM task. Specifically, they were at chance in explicitly determining the direction of motion of the central target. However, reaction times indicated that the patients still showed a dynamic congruency effect. That is, they were much faster to respond in the congruent than in the incongruent trials. Conclusions: Our patients? accuracy and reaction times were normal in the CR task, indicating intact low-level motion processing and a general ability to extract targets in a flanker display. Their failure to explicitly recognize the BM stimuli appears to be independent from the incidental processing and may reflect a stimulus specific, high-level deficit.
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