Effect of distracter preexposure on the reset of an internal clock.

Interruptions and unfamiliar events (distracters) during a timed signal disrupt (delay) timing in humans and other animals. We hypothesized that repeated exposure to a stimulus may reduce its subsequent time-disrupting properties. To test this hypothesis rats were trained in a reversed peak-interval (RPI) procedure, in which dark timing trials were separated by illuminated inter-trial intervals. Rats were then repeatedly exposed to an auditory stimulus (noise) in either dark (DARK group), or illuminated chambers (LIGHT group); control rats were not exposed to the noise (NOVEL group). Afterwards, the time-resetting properties of the noise were tested by presenting it unexpectedly during the (dark) RPI trials. The noise reset timing in NOVEL rats, but stopped timing in DARK rats, suggesting that preexposure reduces the time-resetting effects of distracters. However, in LIGHT rats, the noise stopped timing when the presented early in the RPI trial, but reset when presented late, suggesting that exposure to noise was only partly effective in overriding other relevant variables, such as distracter location. These results suggest that the effect of distracter preexposure on the reset of an internal clock depends on complex associative and temporal interactions which require further investigations. This article is part of a Special Issue entitled: Associative and Temporal Learning.