Fig. 13. Model for visual control of free flight behavior in Drosophila melanogaster. As a fly moves through its environment, a two-dimensional array of motion detectors estimates optic flow (top). The local measurements of optic flow are summed as a rough measure of the image expansion on each side of the fly. The estimates of image expansion are then integrated with respect to time, t. When the time-integrated expansion signal on one side exceeds a threshold, a saccade away from that side is initiated. The time-integrated expansion signal inhibits saccades on the ipsilateral side, preventing a saccade in the opposite direction from quickly following the initial saccade. See Discussion for further details.
