A step function in pigeons' temporal generalization in the peak shift task

Pigeons were reinforced for pecking a key following one signal duration (S+) but not following another signal duration (S-). The S+ and S- were 2.52 and 5.67 sec, respectively, counterbalanced across birds. Subsequent generalization tests with a range of signal durations revealed a step function, with high response rates for all durations on the S+ side of the distribution, low response rates for all durations on the S- side, and an intermediate rate for the intermediate duration. A comparison group of pigeons trained with only the S+ duration showed a fiat generalization function. For the discrimination-trained birds, the delay between signal termination and opportunity to respond was subsequently varied during generalization testing. A step function again appeared, and no evidence of subjective shortening over the delay was found. The overall pattern of results suggests that the birds categorized the temporal signal into two classes and retained a categorical code over the delay.