The Kamin blocking effect with variable-duration CSs

Abstract

The role of temporal uncertainty surrounding the time of US occurrence in Kamin's two-stage blocking paradigm was studied. In Stage 1, stimulus A terminated with the onset of a .5-sec, 1-mA shock US; in Stage 2, a compound stimulus, AX, was similarly reinforced. For different groups of eight rats each, the duration of stimulus A and/or AX was either fixed or was varied from trial to trial. When the stimulus duration was fixed, it predicted the exact time of US onset; when it was varied, it did not. We suspected that uncertainty about the moment of US occurrence might enhance US "surprise." If so, then blocking might be attenuated in the varied CS-duration conditions relative to the standard condition in which both A and AX were fixed. Within the range of temporal uncertainty studied here, however, no significant attenuation of blocking was observed. © 1979 Psychonomic Society, Inc.