A retardation in learning following explicitly uncorrelated presentations of a CS and US has been described as a learned irrelevance effect (e.g., Baker & MacKintosh, Animal Learn & Beh, 5:315, 1977). We reported a learned irrelevance-type effect in appetitive signaled barpressing (D. P. Miller, H. N. Kersten, T. M. Doherty, & J. L. Crouch, SFN Abstracts, 1999). Rats were trained to receive food pellets on a FR-8 partial reinforcement schedule. A group that received 100 pre-exposures to a 1 sec tone/d for 10 d while performing the FR-8 task showed a significant delay in learning a subsequent task that required a barpress during the 1 sec tone period to receive reinforcement. Thus the initial presentations of the tone uncorrelated with the rats' barpress behavior appeared to inhibit subsequent learning when the tone became the only relevant stimulus for obtaining reinforcement. Allen and Gluck (SFN Abstracts, 1997) reported that lesions of the dorsal hippocampus disrupted the learned irrelevance-related ret...