Fig. 3. Quantitative measurements of DCMD firing parameters. This data shows one response of the right DCMD to a `bird' approaching from +45° azimuth. (Top) The raster plot shows the DCMD spike times. (Middle) A Gaussian smoothed (bin=50 ms) plot of the instantaneous firing rate (see text for details). (Bottom) The subtense angle of the `bird' body (B_b) and wing (B_w). From the rate histogram plots I measured the time and amplitude of peak firing (asterisk), the instantaneous spike rate 200 ms before collision (arrow), and the total number of spikes during each approach (see Materials and methods). For this example the DCMD produced 29 spikes and reached a peak firing rate of 165 spikes s^-1 169 ms before collision. At this time the `bird wing' subtended approximately 25° of the right eye's field of view. The point at which the angle of the `bird' wing jumps by more than 3° is 125 ms before collision. Thus in this example the DCMD peak occurred 86 ms (or approximately 7 frames) before a proposed critical subtense angle jump of more than 3° (see Rind and Simmons, 1997).