Analysis of Pigeons' Head and Body Movements While Pecking
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Pigeons have been shown to follow a specific sequence of behaviour while pecking. The pecking motion appears to be a single continuous movement, however video analysis examined at frame rates slower than real-time has shown that pigeons briefly stop the movement of their head twice during a single peck. After the second stop, they initiate a final ballistic movement which terminates when they make contact with a target (Goodale, 1983). It has been hypothesized that during the first stop (or fixation) phase pigeons are making the decision whether or not to peck the target. During the second stop phase pigeons are thought to calculate finer details of the target such as its specific size and depth as well as program the final motor movement needed to make an accurate peck. The current experiment was designed to analyze the function of the second stop phase by varying target size. Four pigeons were trained on a task involving pecking at five sizes of stimuli for a food reward, and the movements of their heads and bodies were recorded during pecking as well as walking towards the screen where the targets appeared. The main hypothesis, that the duration of the second stop phase would increase as stimulus size decreased, was tentatively supported; the data followed the hypothesized trend across all sizes of stimuli except the largest. Other interesting findings concerning head and body movement were also found, such as that pigeons appear to begin calculating the orientation of their head for the final peck during the first stop phase, and that the distances from the screen that the pigeons hold their heads at during both stop phases increase as stimulus size increases. Future directions expanding from these findings are proposed to further examine the function of the first stop phase.