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 pressi ng for food was studied in 48 male hooded rats. Novel stimuli elicited a decrease of the bar press rate. This attenuating effect was the str ongest 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 decre ased the response rate. In contrast, termination of the darkness incre ased the response rate. The difference between auditory and visual sti muli in rapidity of change from attenuating to facilitating effects wa s more evident for shorter than for longer stimuli durations. Summatio n of data from repetitive presentations revealed an overall attenuatin g effect of the visual stimulus and a facilitating effect of the audit ory stimulus on bar press rate.