Representation of global motion in higher visual areas M Furlan, A T Smith |
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Department of Psychology, Royal Holloway University of London, United Kingdom
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| Neuroimaging studies suggest that hMT+ has a role in extracting global motion. However, the role of higher motion-sensitive areas is less clear. We used 3T fMRI and MVPA to test for global motion sensitivity in several motion-processing regions. A novel RDK stimulus was developed in which translational global motion along either of two orthogonal axes could be created using the same set of local motions in both cases. Each dot moved back and forth (reversing direction at 1Hz) along a fixed axis of motion that was assigned randomly. All dots reversed synchronously. In one variant, temporal phases (0 or 180) were assigned so as to produce global translation alternating between 45 and 225deg (the average local direction). In the other, they were assigned such as to produce global motion along the 135-315 axis. Because the local dot motions are the same, differing only in the temporal phase of dot direction reversal, successful decoding of the two stimuli indicates global-motion sensitivity. The results revealed sensitivity in hMT+ but not V1, as expected. However, the best performance was in VIP, CSv, and V6. This suggests that the representation of global motion may first emerge in MT+ then strengthen in higher-level visual regions. |
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