Fig. 8. Collision-avoidance and landing response latencies depend on stimulus position and expansion rate. Latency is measured as the time interval between the onset of image expansion and the initiation of the landing or collision-avoidance response. (A) Latency in response to expansion at a rate of 500° s^-1 is relatively constant over lateral portions of the fly's field of view and increases for positions to the front and rear. Data points represent mean latency ± S.E.M. for 12 flies. (B) Landing response latency to a square expanding at 500° s^-1 is constant at the stimulus positions at which landing response probability is high. At this expansion rate, the collision-avoidance latency is approximately half that of the landing response. (C) Response latencies plotted as a function of expansion rate. For a given rate of expansion, the minimum of the mean delay functions (such as the two plotted above) was determined. Filled circles represent the minimum mean delay in the landing response, while empty circles represent the minimum mean delay of the collision-avoidance response. The landing response latency decreases with the rate of expansion, whereas for most expansion rates the delay of the collision-avoidance response is constant.