LEARNING AND MOTIVATION 8, 533-550 (1977) Temporal Properties of Responding during Stimuli that Precede Response-Independent Food STEVE R. OSBORNEANDPETER R. KILLEEN Arizona State University Pigeons’ keypecks were reinforced with grain on the average of once per minute by schedules that maintained low response rates and by schedules that maintained high response rates. During these schedules, a fixed-duration conditioned stimulus (CS) ranging from 7.5 to 120 set in duration across conditions terminated with response-independent food. Response rates during the CS were inversely re- lated to CS duration. The rates and the temporal patterns of responding during the shortest CS were similar whether the ongoing schedule maintained high re- sponse rates or low response rates. As CS duration increased, the rate and pattern of responding during the CS converged on the rate and pattern of responding main- tained by the baseline schedule. These data indicate that changes in responding during stimuli that signal response-independent reinforcement are not homogeneous throughout the CS; that response measures, such as “suppression ratios,” which presume homogeneity may mislead us; and that conditioned suppression and conditioned enhancement may be better talked about in terms of species-specific approach and avoidance than in terms of emotional states. Responding is disrupted if a stimulus followed by electric shock is superimposed upon a schedule of food presentation (Estes & Skinner, 1941). Responding is also disrupted if the stimulus is followed by response- independent presentations of a positive reinforcer (e.g., Herrnstein & Morse, 1957). Although preaversive stimuli typically suppress baseline responding (Annau & Kamin, 1961; Carleton & Didamo, 1960; Stein, Sid- man, & Brady, 1958), both suppression and enhancement of responding have occurred during prereward stimuli. Pigeons show enhanced respond- ing during short prereward stimuli (LoLordo, 1971) and mixed effects for long-duration stimuli (Hermstein & Morse, 1957). On the other hand, for nonavian species, response suppression has been reported with short pre- reward stimuli, no effect with intermediate-duration stimuli, and either no effect or response rate enhancement with long-duration stimuli (Azrin & Hake, 1969; Henton & Brady, 1970; Meltzer & Brahlek, 1970; Miczek & Grossman, 1971). The rate of responding maintained by the ongoing schedule also affects This research was supported in part by NSF Grant No. BMS-74 23566, P. Killeen principal investigator. Requests for reprints should be sent to S. Osborne, Department of Psychology, Arizona State University, Tempe, Arizona 85281. 533 Copyright 0 1977 by Academic Press, Inc. AI1 rights of reproduction in any form reserved. ISSN @X23-%90