Psychology, Department of


Date of this Version

March 1993


Published in Journal of Experimental Psychology: Animal Behavior Processes, 19:3 (1993), pp. 255–264. Copyright © 1993 by the American Psychological Association. Inc. “This article may not exactly replicate the fi nal version published in the APA journal. It is not the copy of record.” xan/. Used by permission.


Conditioned suppression was used with rats to study the effects of extending conditioned stimuli (CSs) before versus after the delivery of unconditioned stimuli. These extensions are termed B and A extensions, respectively. Within-group designs were used to compare the effects of extending CSs when 2-min parts of those CSs were separated by temporal gaps of 6 min versus a separation of no gap. The results were as follows: (a) B extensions weakened conditioning more than did A extensions, with or without gaps; (b) under some conditions, this asymmetrical effect persisted with extended training; (c) gaps between 2-min parts of a B extension had no detectable effect; and (d) under some parameter values, gaps between 2-min parts of an A extension weakened conditioning significantly. These results are better predicted by the Sometimes Opponent-Process model (SOP; A. R. Wagner, 1981) than by the Rescorla-Wagner-Frey-Sears real–time model (J. J. B. Ayres, M. Albert, & J. C. Bombace, 1987).