Short-term incidental memory for irrelevant cues.

A new analysis of previously published studies of delayed matching-to-sample (DMTS) water-escape and the results of a new food-reinforced discrimination study are presented. In both cases, male Sprague-Dawley rats demonstrated short-term incidental memory for irrelevant cues in the context of two-alternative forced-choice problems that required learning about relevant cues. In the DMTS experiments, relevant and irrelevant cues were place or brightness. In the discrimination experiment, the relevant cues were place, brightness or a visual-tactile maze insert. In all experiments, after the rats attained high-level performance, consistently making choices with respect to the relevant stimuli, response latencies to the correct relevant cue were shorter when the irrelevant cue value(s) was the same as on the immediately preceding trial. These latency differences are interpreted as indicating that the rats demonstrated short-term incidental memory for the irrelevant cues. This mnemonic phenomenon resembles priming, an implicit form of memory.