Fig. 9. Reconstruction of the fly’s visual environment and estimation of optic flow by local motion detection. (A) Reconstruction of the fly’s visual environment is based upon the fly’s position (red circle) and its heading (red arrow) for both the textured (top) and uniform (bottom) backgrounds. Both cases represent the position of a fly 500 ms before a saccade. (B) Calculation of the fly’s visual environment from its position. The projection (in spherical coordinates) of each portion of visual texture onto the fly’s retina was calculated. For example, the regions indicated by the numbers in A map to those in B. A frame representing the mapping of the fly’s visual environment onto its retina at a single point in its flight, similar to that shown in B, was determined for each point along its flight trajectory. (C) Output of local motion detectors. A motion-detection algorithm using delay and correlate motion detectors was applied to this series of frames, resulting in local calculations of horizontal and vertical motion, which are represented by a vector field. Vector fields representing the mean response of the output of the horizontal and vertical motion detectors taken over the 500 ms preceding a saccade are shown in this figure. Note that the spacing of the inputs and outputs of the elementary motion detector was 5°; every second arrow has thus been omitted for clarity. Top, textured background; bottom, uniform background.
