A dynamic object-processing network: metric shape discrimination of dynamic objects by activation of occipitotemporal, parietal, and frontal cortices.

Shape perception is important for object recognition. However, behavioral studies have shown that rigid motion also contributes directly to the recognition process, in addition to providing visual cues to shape. Using psychophysics and functional brain imaging, we investigated the neural mechanisms involved in shape and motion processing for dynamic object recognition. Observers discriminated between pairs of rotating novel objects in which the 3-dimensional shape difference between the pair was systematically varied in metric steps. In addition, the objects rotated in either the same or the different direction to determine the effect of task-irrelevant motion on behavior and neural activity. We found that observers' shape discrimination performance increased systematically with shape differences, as did the hemodynamic responses of occipitotemporal, parietal, and frontal regions. Furthermore, responses in occipital regions were only correlated with observers' perceived shape differences. We also found different effects of object motion on shape discrimination across observers, which were reflected in responses of the superior temporal sulcus. These results suggest a network of regions that are involved in the discrimination of metric shape differences for dynamic object recognition.