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Fig. 4 Self-induced change in optic flow direction does not cause Purkinje cell (PC) activation. (A) Average motor activity (bottom, red) during forward optic flow at 1 cm/s, negative probe, positive probe, and no optic flow stimuli (top, green). (B) Forward optic flow reliably evoked swims, whereas very few and no swims were seen in response to positive probe and negative probe stimuli respectively. N = 8 fish, **P = 0.0006 by Friedman’s test, P = 0.011 (forward flow versus +ve probe) and P = 0.002 (forward flow versus −ve probe) by post hoc Conover’s test. (C) Example forward optic flow stimulus at 1 cm/s (top), motor activity (middle), and the resultant net optic flow experienced by the fish in closed loop (bottom). (D) Motor onset triggered average optic flow stimulus (green, top), swim velocity (pink, top), and net optic flow experienced by the fish (middle). Bottom panel shows average calcium responses in backward-tuned PCs aligned to motor onset. (E) Probe triggered average optic flow (green, top), swim velocity (pink, top), and average net optic flow experienced by the fish (middle). Bottom panel shows the average calcium responses in backward-tuned PCs aligned to probe onset. (F) Same as (D) for swim events lasting longer than 0.75 s. (G) Magnitude of the negative component of optic flow during swims is much larger than the amplitude of the negative probe stimulus. (H) Peak amplitude of the calcium response in backward-tuned cells to the negative probe stimulus is much larger than the response to swim bouts. (I) The slope of the rise phase of the calcium response in backward-tuned cells is significantly steeper for the negative probe stimulus than during motor activity. N = 7 fish, *P = 0.016 [(G) and (H)] and 0.03 (I) by Wilcoxon signed-rank test. Shaded areas in (D) and (F) represent SEM across eight fish.