Figure A2.

Receptive field of vCH in Eristalis and Calliphora. Each plot shows the receptive field of vCH in a window of >140° elevation and >160° azimuth. The false color map behind the local preferred directions codes for the mean response amplitude of the cells to movement from the left to the right at seven different elevations. The false color map was interpolated to avoid hard edges of binning the data. The superimposed arrows show the local preferred directions (length codes for local sensitivity). Black arrows are samples. Gray arrows are linearly interpolated. To determine the receptive fields a narrow but high (2° × 10°) target was presented to vCH neurons which traversed the complete field of view horizontally at seven different elevations in both directions. In addition, the same target, rotated by 90°, was presented on a vertical trajectory at seven different azimuths. The local direction preference of the vCH cell (Figure A2) was calculated as follows: At first we corrected for the latencies of the cells. We calculated the latency from the replay experiments (see Materials and Methods), by calculating the mean time difference between the saccade velocity peak and the response amplitude peak. For each movement direction adopted by our bar stimulus (left to right, right to left, top to bottom, bottom to top) we calculated the mean response across cells. We treated the membrane potential change as the length of a vector pointing in the direction of target motion. Summation of all four vectors yielded the preferred direction vector. The length of this vector was set to represent the local direction sensitivity. This was done at all locations within the sampling grid. The color map behind the local preferences shows the mean interpolated reaction of the cells to left-to-right motion. (A) Receptive field of Eristalis vCH (n = 3), (B) receptive field of Calliphora vCH (n = 4).