Figure 6.

Timing of sequenced swim bouts depends on updated stimulus location. (A) Time course of fish-target angle ϕ and caudal tail angle γ₅ during a pair of swim bouts evoked by a moving target in a restrained larva. First swim was directed toward a stimulus moving in the periphery (35–55°). Onset of the first swim triggered a translation of stimulus/background stopping short 10° from the midline, simulating an undershoot in turning. The end of the first swim triggered stimulus motion at constant velocity toward the contralateral hemifield, evoking a second, target-directed swim. Inter-bout-interval (IBI) indicated by vertical lines. (B) Same as in panel (A), but with the stimulus/background translated to the center of the visual field (0°) during the first swim, simulating exact alignment of the larva with the location of prey (“on-target”). Note that the IBI is considerably shorter. (C) Same as in panel (A), but with the stimulus/background translated beyond the center of the visual field by 10° during the first swim, simulating an overshoot in turning. (D) Dependence of IBIs on the update location of the stimulus during the first swim bout. Trials with initial stimulus position on the left or right side were interspersed and pooled. Negative values of update location represent an undershoot; positive values an overshoot during the first swim. Data from n = 6 fish. (E) Data from recordings of freely moving larvae performing prey capture sequences. Scatter plot of IBIs between first and second swim bout in which the fish-target angle ϕ_post (measured at the end of the first swim) varied between ±15°. Negative values correspond to an undershoot, positive values to an overshoot in turning. Note the minimum in IBIs for small turning error near ϕ_post = 0°. Solid line is a Gaussian fit curve.