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Tao Zhang, Kenneth H. Britten; Responses to heading stimuli in macaque VIP. Journal of Vision 2002;2(7):503. doi: 10.1167/2.7.503.
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Higher-order areas in the “motion system” of dorsal extrastriate cortex have been implicated in the analysis of “optic flow” stimuli, which can support perception of observer heading. The ventral intraparietal area (VIP) is near the top of this system, receives dense input from areas MT and MST, and has briskly directional visual responses to optic flow stimuli. Furthermore, visual responses in VIP can encode stimuli in “head-centered” coordinates, suggesting integration of eye position and visual inputs. Such integration would be particularly useful in recovering heading in the presence of gaze rotation caused by smooth pursuit eye movements.
In a preliminary test of the role of VIP in optic flow and heading perception, we measured the responses of VIP neurons to a battery of optic flow stimuli, including linear motion, complex (“spiral space”) motion, and heading stimuli simulating a range of observer motions varying in the horizontal plane. Heading stimuli simulated observer translation towards a cloud of points in 3 dimensions, and subtended about 70 by 50 degrees of visual angle. The range of headings was centered over the cells' RFs, and responses were measured with and without superimposed horizontal smooth pursuit.
Most VIP responses are significantly modulated by varying horizontal heading. Typically, tuning is monotonic and sigmoidal across the range of headings tested. The shift of this tuning in the presence of smooth pursuit is very modest, indicating nearly complete compensation for smooth pursuit eye movements. Our results suggest that VIP is involved in heading perception and in the compensation for observer-caused gaze rotations.
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