Associative modulation of the orienting response: Distinct effects revealed by hippocampal lesions

The ability of auditory stimuli to modulate rats' tendency to orient to vis ual targets was assessed. In Experiment I, trials where an auditory stimulu s (A) signaled one visual array (X) were intermixed with unsignaled present ations of a second array (Y). Comparison of the orienting responses (ORs) t o X and Y revealed that A produced a transient (unconditioned) and an emerg ing.(conditioned) disruptive influence on the OR to X. In Experiments 2 and 3, trials where A signaled X were intermixed with others where another aud itory stimulus (B) signaled Y. Stimulus A's ability to modulate the OR to X was then assessed by presenting A prior to test arrays containing both X a nd Y. Control rats were more likely to orient to Y than X (Experiments 2 an d 3) and rats with excitotoxic lesions of the hippocampus were more likely to orient to X than Y (Experiment 3). These results show that auditory stim uli exert distinct modulatory influences on the OR to visual stimuli with w hich they are associated.