Separate neural pathways for contour and biological-motion cues in motion-defined animal shapes

Abstract

To determine whether contour and biological motion (BM) cues for motion-defined shapes are subserved by two separate mechanisms, we used PET to measure regional cerebral blood flow in nine human subjects. Subjects were scanned in the following four conditions: (1) contour-defined animals with natural movements (running), (2) motion-defined animals in which the contours were removed and dots were placed on the limbs and moving parts (BM; running); (3) drifting static animal shapes (contours); and (4) drifting dots. The results demonstrate that the perception of BM involves the superior frontal gyrus, the precuneus, the fusiform, the lingual and the medial temporal gyri, the inferior parietal lobe, the hippocampal and parahippocampal areas, and the cerebellum. In addition, the anterior cingulate cortex and the amygdala were significantly activated. The perception of contour-defined shapes produced significant elevation of rCBF in some areas similar to the BM condition, namely the fusiform, medial occipital, medial temporal, and lingual gyri. Only the occipital pole and the inferior temporal cortex were specifically activated by contour-defined shapes. These results are congruent with previous findings that the dorsal visual pathway is important for the perception of BM. They further support psychophysical results showing that contour and BM cues for motion-defined animal shapes are processed by independent channels.