The integration of higher order form and motion by the human brain.

Our experience with a dynamic environment has tuned our visual system to use form and motion as complementary sources of information for object recognition. To identify the neural systems involved in integrating form and motion information during dynamic object processing, we used an fMRI adaptation paradigm which factorially manipulated form and motion repetition. Observers were sequentially presented with pairs of rotating novel objects in which the form or rotation direction in depth could be repeated. They were required to discriminate either dimension of the second target object, while the first object served as a form and/or motion prime. At the behavioural level, observers were faster to recognize the target or discriminate its direction when primed by the same form. Importantly, this form priming effect was enhanced when prime and target objects rotated in the same direction. At the neural level, the two priming effects (i.e., the main effect of form repetition and the interaction between form and motion repetition) were associated with reduced activations in distinct brain regions. Bilateral lateral occipital regions exhibited reduced activation when form was repeated irrespective of rotation direction. In contrast, bilateral anterior fusiform and posterior middle temporal regions (overlapping with hMT+/V5) regions showed an adaptation effect that depended on both form and motion direction. Thus, the current results reveal a visual processing hierarchy with lateral occipito-temporal cortex representing an object's 3D structure, and anterior fusiform and posterior middle temporal regions being involved in spatio-temporal integration of form and motion during dynamic object processing.