Predictions of Drifting Grating Responses

A grating drifting across the receptive field is identical to a set of sinusoidally-modulated stationary bars if the bars are in the proper phase arrangement. We can therefore estimate the response to a grating by adding up the responses to the bars after shifting the histograms appropriately.

The predicted response is where r(t) is the response at time t to a bar at position x and temporal frequency w, and f is the spatial frequency of the simulated grating.

Figure 4 shows the original 2Hz control histograms in red, and the same histograms after shifting them by xf/w in diagonally-hatched colors. Figure 5 then shows the sum of these shifted histograms by stacking them on top of each other, as well as the sum shown by a black line. The sum is actually computed more continuously than the stacked histograms, which are shifted by an integral number of bins, so that the black line is smoother.

Figure 4

Figure 5

This process was applied to both the control and adapted responses, and figure 6 shows the results (the sum shown above is divided by the number of positions tested, 8). The stationary maps suffice to predict the timing aftereffects seen with drifting gratings. Thus, the timing aftereffects seen with moving stimuli do not depend on some dynamic, nonlinear process, but instead arise from receptive field structure.

Figure 6

Next section is Effects of Adapting on Localized Responses.

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