Timescale dependence in a conditional temporal discrimination procedure.

A conditional temporal discrimination procedure was used to test the scope and generality of the principle of timescale invariance (TSI). Rats were trained to make different temporal discriminations following four different auditory stimuli. After shorter stimuli, rats were reinforced for pressing the left lever, and after longer stimuli, rats were reinforced for pressing the right lever. The four auditory stimuli (a pure tone, pulsed tone, click, and white noise) were each presented for different pairs of durations (ranging from 2 vs. 8s to 32 vs. 128 s) within a single session, but the ratio between the shorter and longer duration was maintained constant at 1:4. With the shortest pair of durations (2 vs. 8s), rats showed a clear violation of TSI in both overall and relative response rates. Rats started responding later and persisted relatively longer on the left lever when the shorter duration was only 2s. We interpret these results with regards to a framing hypothesis, whereby TSI does not apply to relatively short durations when animals are simultaneously trained with wide ranges of intervals.