Effects of age on short-term memory for time in rats

Working memory (WM) for event duration was investigated in four different age groups of rats (6, 12, 18, and 24 months), using a delayed, symbolic-matching-to-sample procedure. In an initial experiment, all age groups responded as though a long sample duration were a short one when retention intervals (RI) were applied. This effect is called the choose-short effect. In a second experiment, in order to test whether, in compliance with the subjective-shortening model, there would be a "shortening" of the sample duration according to the length of the RI, the psychophysical function relating the probability of choosing the long comparison stimulus to sample duration and the point of subjective equality (PSE) were determined across successive RIs in two age groups (6 and 18 months). A significant shift of the psychophysical function towards a longer duration and a significant increase of the PSE appeared as a function of the RI in 6-month-old, but not in 18-month-old rats. These results support the idea that the choose-short effect is due to a shortening of the event duration in the WM in young animals, whereas there is no evidence that the sample forgetting occurred on a time dimension in older rats.