Fig. 1. The retinal size and position of the dummy on the crab's retina at the time of response. Each measure is plotted as a histogram against the dummy's approach direction (track angle; see inset at the top). Vertical lines mark 1 S.E.M.. above and below the mean. (A) Vertical retinal size increases with track angle (REML; N=419, Wald/d.f.=31.86, d.f.=8, P<0.001). The results for the horizontal angular size of the dummy are equivalent. (B) Dummy elevation in the crabs' visual field at the time of response increases with track angle (black bars). The elevation of the burrow (grey bars), by contrast, varies little, indicating that the crab-burrow distance was relatively constant across different track angles. (C) The azimuth directions relative to the burrow at which the dummy is seen become larger with track angle. Due to the strong asymmetry of these distributions, means for A and B were determined on a logarithmic scale.

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