The choose-short effect in rat memory for event duration: the subjective-shortening model

Two predictions derived from the subjective-shortening model were tested in rats. The predictions concerned the temporary occurrence of the choose-short effect with extended training at a given retention interval (RI) and the occurrence of a temporary choose-long effect, when RIs shorter than those used during training were applied. In a first experiment, using a stepwise delay procedure with training 0-s RI sessions interpolated between each series of increasing RIs, results showed: (1) a choose-short effect during the stepwise increase in the delay procedure, (2) a temporary occurrence of the choose-short effect during testing at a given RI and (3) a choose-long effect in half of the animals, when a RI shorter than that used previously was applied. These contrasting results suggest that the disappearance of the choose-short effect could be, as proposed by the model, either the consequence of the foreshortening of the reference memory (for rats choosing-long) or the consequence of an adaptation of the working memory (for rats which did not choose long). Results were discussed in relation with the procedure which could have contributed, by the interposition of 0-s RI sessions, to maintain a stable reference memory. In order to test this interpretation, a second experiment, using the classical stepwise delay procedure without training sessions interpolated, was carried out. In these conditions, rats did never present a significant choose-long effect when the RI was shortened. These results suggest that rats maintained a stable reference memory and could improve their performances during retention testing sessions either by an adaptation of their working memory or by the adoption of an alternative strategy which consisted in learning to maintain an orientation towards the location of the correct lever.