Fig. 4. Threshold of escape response to looming stimuli. Individual responses from different crabs are displayed from the beginning of stimulus expansion up to 0.5 s following the time of virtual collision (same dataset as shown in Fig. 3). The time at which each response was initiated (response latency) was projected onto the curve that describes the angular size of the stimulus, which identifies the apparent stimulus size at the time the crab initiated the escape response. The inset shows at higher magnification the part of the responses corresponding to the time enclosed by the horizontal rectangle. See the text for further details.