Figure 3. The optomotor response in virtual reality.

(a) A schematic of the experimental setup. The tail was imaged using a high-speed camera, an IR LED for illumination, and a high-pass filter to prevent the visual stimulus from reaching the camera. A projector was used to display the moving grating on a diffusive screen placed 0.5 cm below the larva. The larva was head-embedded in low-melting agarose at the bottom of a petri-dish. The tail was free to move. (b) The grating moved at 1 cm/s. θ represents the difference between the larva’s heading direction (green arrow) and the direction of the moving grating (yellow arrow). (c) Center panel: example of the changes in θ for one larva (20 trials). Left panel: Initial distribution of θ for the same larva. Right panel: Final orientation (θ_t=6s) distribution. The initial orientation distribution (θ_t=0) is superimposed in blue for comparison. (d) Left panel: Initial orientation distribution for all larvae and all trials for which at least one bout was generated. Center panel: color-coded density of trajectory as a function of time for the 6 s trials. Left panel: Initial distribution of θ_t=0 for all larvae. Right panel: Final orientation distribution (θ_t=6s) for all larvae. (e) Proportion of larvae aligned with the moving stimuli () as a function of time during the trial. The time scale is common to (c), (d) and (e). (f) Histogram of latency as a function of the initial orientation of the grating, error bar indicates s.e.m. (g) Average of |θ|, for successive bouts, error bar indicates s.e.m. (h) Average percentage of trajectories aligned with the moving stimulus (), at the beginning and at the end of the trials, for each larva. The average is shown in red.