Fig. 5. Effects of absolute target speed on response amplitude and image blur. (A,B) Mean response amplitudes V of 7 male (A) and 7 female (B) photoreceptors to simulated target stimuli, plotted against absolute target speed u. The optimum male response occurs at speeds between 10 cm s^-1 and 80 cm s^-1, for targets at distances of up to 33 cm. (C,D) Mean spatial blur factor _v/_x of the same male (C) and female (D) photoreceptors to simulated target stimuli, plotted against absolute target speed u. The male achieves blur factors of less than 1 for slow moving targets at distances of <15 cm. Motion blur begins in both sexes when the target is travelling at approximately 50 cm s^-1.