Figure 4.

Most tongue projections are preceded by a fast and accurate, fixed-duration head turn. Head turns were defined as head rotations exceeding 5 degrees in amplitude and 10°/s in angular velocity. All panels: n = 268. A, Left, Orienting head turns (head turns not followed by a tongue projection) brought the prey image from the periphery of the salamanders field of view into the binocular zone. Right, Projection head turns (head turns immediately followed by a tongue projection; see Materials and Methods) began with the prey within the binocular field of view and ended with the prey tightly centered around the visual mid-line. B, Angular velocity of all recorded orienting and projection head turns. Arrow indicates one x-shifted data point with head turn amplitude of 124°. C, Distribution of orienting and projection head turn durations. Projection head turns were less variable and had a significantly shorter duration compared with orienting head turns (123 ± 4.0 ms vs 264 ± 16 ms, mean ± SEM, n = 186, n = 113; unpaired t test, p < 0.0001). D, Distribution of the angle between the head direction and tongue direction relative to the visual mid-line (see Materials and Methods). The tongue was projected along the visual midline on average, but deviations up to ±5° were common. E, Distribution of tongue projection error and head orientation error, relative to prey position.