Fig. 10.

Distribution of angular differences between the directions of reversal of optic flow selectivity and the preferred direction for full-field, frontoparallel, unidirectional motion. The direction of reversal of the optic flow selectivity was obtained by fitting a two-dimensional linear regression to 9 or 18 data points. To determine the direction of maximum change from expansion to contraction (or clockwise to counterclockwise rotation, respectively), we performed a regression on the difference between the activity recorded during expansion and the activity recorded during contraction. The gradient of the regression indicates the direction in which the selectivity changes maximally from contraction to expansion. This direction was then subtracted from the preferred direction for full-field, frontoparallel, unidirectional motion. The experimental distributions (top graphs) show a clear correlation between the directions of reversal and the preferred direction: the distributions peak at 180° angular difference for expansion/contraction (top left) and 90° angular difference for rotation (top right). The distributions for 250 randomly selected model neurons (bottom graphs) display the same correlation. Thus, a correlation between the optic flow responses and the directional selectivity is obvious for most neurons, but it is consistent with an involvement in optic flow analysis.