Figure 5.

One- and two-plane stimulus. a, Sketch of a two-plane stimulus and its component planes. The two-plane stimulus was made up of a plane of dots moving in the preferred direction and another moving in the null direction. The two planes were always positioned symmetrically around the fixation point with opposite signs but the same magnitude of absolute disparity. In the example, the preferred direction plane (black) is at an absolute disparity of −0.2° (near), and the null direction plane (red) is at +0.2° (far). The relative disparity of the associated two-plane stimulus is −0.4°. In these experiments, the disparities of two-plane stimuli are identified by the absolute disparity of the preferred plane (−0.2°). Interleaved with the two-plane stimulus, individual planes were presented separately at the same disparities as in the two-plane stimulus (with reference to Fig. 1b, the two-plane stimulus set used here would fall along the green line in Fig. 1b labeled ped = 0 plus the individual preferred and null component planes that make up the two plane stimuli). The black cross and line depict the fixation cross and plane of fixation respectively. b, Neuronal tuning curves were plotted to compare for each disparity the response to the two-plane stimulus with the responses to the individual planes that made up this two-plane stimulus. The absolute disparity of the preferred plane is represented on the x-axis at the bottom of the graph, with the absolute disparity of the null plane at the top. The V5/MT neuron in this example was tuned to a plane of dots moving in the preferred direction presented at a negative disparity (near); there was little response to a plane of dots moving in the null direction at any of the disparities tested. Presenting both planes together did not change the sign of the disparity preference (negative), but the disparity tuning became sharper. c, Another V5/MT neuron from a different animal showed marked attenuation in the response to the pref stimulus when the null plane was added, again without altering the overall disparity preference of the neuron. In b and c, the green line represents the simple regression fit to the two plane responses based on the single plane responses for Equation 6, and the blue line represents the fit for Equation 7, including the interaction term.