Habituation of the orienting response to auditory and visual stimuli in rats trained to press a bar.

Habituation of the effects elicited by presentation of novel auditory (wide band noise) and visual (darkness) stimuli on on-going bar pressing for food was studied in 48 male hooded rats. Novel stimuli elicited a decrease of the bar press rate. This attenuating effect was the strongest on the first onset of the stimulus of a given modality and then slowly decayed during the stimulus action. The effect from the noise stimulus habituated more rapidly than that elicited by darkness. Then, noise onset enhanced bar pressing, and termination of the noise decreased the response rate. In contrast, termination of the darkness increased the response rate. The difference between auditory and visual stimuli in rapidity of change from attenuating to facilitating effects was more evident for shorter than for longer stimuli durations. Summation of data from repetitive presentations revealed an overall attenuating effect of the visual stimulus and a facilitating effect of the auditory stimulus on bar press rate.