Figure 1.

Quantitative analysis of salamander tongue projection accuracy and prey motion. A, Salamander and fruit fly (prey) were paired in a behavior arena, and prey capture was filmed at 4000 frames per second. Infrared illumination under the translucent arena floor provided adequate contrast in the camera image, whereas white LED dome lights set the visible light level for the behavior. B, Projection accuracy was defined as the angle between the line from the reference point midway between the two eyes to the prey (blue line) and the line from the reference point to the center of the tongue pad at the end of the extended tongue (magenta line). C, Example of the salamander inter-eye distance during a single predation event. Inter-eye distance decreased rapidly at the onset of the tongue projection (asterisks). These rapid decreases were used for automated detection of all tongue projections (hits and misses) in the recorded image sequence. Changes in inter-eye distance associated with tongue projections were distinguished from those caused by other behaviors, such as head turns and eye retractions (arrows) based on their faster temporal kinetics and larger amplitude, as calculated from an exponentially decaying function fit to the data (red lines), triggered by a deviation exceeding 0.2 mm from the moving average intereye distance (25 ms window). D, Schematic representation of the three tongue guidance models tested in this study. At time t₂, the salamander detects the prey and initiates prey capture. However, due to sensorimotor delays, it sees the prey image lagged in the past, at position t₁. Motor delays prevent the tongue from contacting the prey until it attains position t₃. The prey moves throughout this process, and the salamander can thus aim at (i) the visuomotor-lagged position of the prey, compensating for neither delay; (ii) the motor-lagged position of the prey, compensating only for the visual delay; or (iii) the extrapolated position of the prey, compensating for both delays.