Timing in pigeons: The choose-short effect may result from pigeons’ “confusion” between delay and intertrial intervals

Abstract

In conditional discriminations, when samples differ only in duration, pigeons typically show a choose-short effect (i.e., higher matching accuracy on short-duration-sample than on long-durationsample trials with increasing delay between sample and comparison stimuli). That this effect depends on the similarity of retention interval (RI) and intertrial interval (ITI) houselight illumination conditions has been taken as evidence that pigeons judge duration relative to a temporal background. In the present experiment, pigeons trained with duration samples and with the ITI either illuminated or not showed a choose-short bias only when the RI illumination on test trials was the same as the ITI illumination had been in training. The results support the hypothesis that the choose-short effect results from the pigeons’ confusion between the ITI and the RI.