We developed a video system for real-time detection of a pigeon's orientation and for reinforcement of a “turning response.” Using this system, negative behavioral contrast was found across key-peck and turning responses. In addition, turning away from the pecking key was detected by the system just after presentation of the negative discriminative stimulus on the key. The results suggest that avoidance of the discriminative stimulus in the constant component, which has been regarded as a causal factor for negative contrast (additivity theory), is not the primary factor for negative behavioral contrast of pigeons' key pecking, but may account for negative local contrast.
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