Figure 4. Prey-capture behavior in virtual reality.
(a) Schematic of the experimental setup. The larva is positioned on an elevated stage in the center of a cylindrical recording chamber. Visual stimuli were projected on a screen surrounding the recording chamber, covering a field of view of 180°, and centered around the direction of the larva’s head. The tail was imaged using a high-speed camera mounted on a binocular. For illumination, an IR LED was placed below the chamber. Two projectors were used to project the virtual prey, each covering a field of view of 90°. (b) Presentation of the virtual environment during each trial. (i) The virtual prey of 4° appeared from either side of the larva with an angular speed of 20°/s. (ii) After the onset of the first tail bout, the angular speed of the virtual prey was set to 0°/s and its position on the screen was further updated according to the larva’s tail movements only. (iii) A trial was considered successful if the larva got at least 400 μm from the virtual prey. (c) Percentage of trials that ended in successful capture of the virtual prey. Only trials where larvae executed at least one tail bout were considered. Left: Each dot represents the performance of individual larvae. Right: The performance obtained by shuffling the angular positions of the virtual prey in each dataset. The red segment depicts the average. (p = 1.4*10−5, Wilcoxon signed-rank test). (d) Examples of paths of a larva towards the virtual prey. The paths are color-coded according to the position of the virtual prey at the onset of the first tail bout (color bar). Upper panel: Individual paths for one larva. Left: Paths leading to capture. Right: paths failing to capture the virtual prey. Lower panel: Superposition of the trajectories from all larvae (N = 27). Each bin of the meshgrid is color-coded according to the average position of the virtual prey for the trajectory in that bin (color bar). Left: paths leading to capture. Right: Paths failing to capture the virtual preys. In all panels, the black arrows indicate the initial position of larvae. (e) Distribution of the angle of the virtual prey at the bout’s onset in the first trial. (f) Proportion of bouts in each category of movement, during the trials (virtual-prey stimuli) and between trials (spontaneous). Not Significant: *p > 0.05, p < 0.05, **p < 0.01, ***p < 0,001. (g) Proportion of bouts in each category of movement for successful or unsuccessful trials. (h) Change in head orientation for the first three bouts. Only trials in which larvae performed at least three bouts were considered. Error bar: s.e.m.