Abstract
According to current models of motion detection, cortical motion sensors are tuned in both space and time to create spatiotemporally-oriented receptive fields. Motion direction is encoded by summing activity across sensors tuned to the same direction, and subtracting the outputs of sensors tuned to different directions. A psychophysical adaptation experiment tested for (i) subtractive interactions between sensors tuned to different directions and (ii) spatiotemporal tuning in motion sensing receptive fields. Participants viewed a counter-phase stimulus containing superimposed saw-tooth gratings moving in opposite directions. The contrast of one grating (pedestal) was fixed, while the contrast of the other (test) was varied to establish a motion null (no net apparent motion in the counter-phase). After adapting to a single grating drifting in the same direction as the test component, more test contrast was required to achieve a null relative to baseline. After adapting to a grating drifting in the opposite direction to the test component, less contrast was required to achieve a null. When both adapting and test gratings were counter-phase gratings, a small degree of test contrast threshold elevation was found which depended on the spatiotemporal phases of adapting and test components, consistent with spatiotemporally tuned motion sensor receptive fields.