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Fig. 7 Strong population-wide representation of stimulus expectation correlates with lower swim latency. (A) Left: Schematic of the experimental preparation. Right: Traces showing the optic flow stimulus, PC recording with SSs and CF inputs, fictive motor recording, and the processed motor signal used for closed-loop feedback for some fish. Scale: zoomed-out, 2 s; zoomed-in, 20 ms. (B and C) Both SS (B) and CF input (C) rates show a significant, steady increase before the onset of optic flow. ***P < 0.001 by linear mixed-effects. n = 20 cells in (B) and n = 15 cells in (C). (D) Regression-based classification of cells into forward (magenta)– and backward (black)–tuned. Gray traces represent individual fish, N = 27. (E to G) The pre-flow calcium activity is significantly anticorrelated with latency for the forward-tuned cells (E). No correlation is seen after shuffling trial order (F) or in backward-tuned cells (G). Slope and P value by linear mixed-effects are inset in each plot. N = 27 fish. (H) The pre-flow calcium activity in forward-tuned cells is significantly anticorrelated with latency up to 2.5 s before the onset of the forward optic flow stimulus. (I) Heatmap of single-trial responses of all cells in a representative fish to two instances of the negative probe stimulus. The average motor activity over a window of 10 nonprobe stimulus pulses around each of the probes is shown on top. The mean latency to initiate swims and the population-wide probe response probability are inset in each plot. (J) Representative plot from one fish showing latency to swim in response to forward optic flow (pink) along with probe response amplitude (black) and probability (black dashed) for backward-tuned cells. (K) Both amplitude and probability are anticorrelated with latency. Green-shaded area shows 95% confidence interval for the median estimated by bootstrapping. N = 16 fish.