Fig. 6. Escape path of a crab having a large orientation error when it was frightened. (A) crab's transverse body axis during foraging (black arrows) and escape (gray arrows); it was frightened at t=65. Foraging behavior was digitized at 1 frame s^-1, while escape was digitized at 25 frames s^-1. (B) Plot of egocentric running direction (dotted line) and egocentric home direction (solid line) plotted against time during escape (i.e. from 65 to 65.4 s); (C) Changes in orientation (body turns; solid line) and changes in egocentric running direction (dotted line) during fast escape. (D) Time course of running velocity of escaping crab (open circles) compared to the similar time course for eight other escaping crabs (gray circle, broken gray line shows ± S.D.). For correlating two behaviors in time, it must be remembered that turns and running direction are first derivatives of orientation (a position measurement), and change in running direction is a second derivative of orientation. It then follows that, if orientation has n observations, then turns and running direction have n-1 observations, and change in running direction has n-2 observations. We therefore associate the `nth' turn or running direction with the nth orientation (see running direction vs. home direction in B), and the nth change in running direction with the nth+1 turn (see running direction change vs. orientation change in C).

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