Administered 64 male albino rats 40 acquisition trials with 100% (CR) or 50% (PR) reinforcement in a straight runway followed by 28 extinction trials. Within each reinforcement group 16 Ss received injections of saline or of amobarbital sodium (20 mg/kg) prior to each daily block of 4 trials in acquisition, and within each of these subgroups 1/2 were maintained on the same injection condition and 1/2 were switched to the other condition for extinction. Extinction performance was increased by PR and by amobarbital in extinction, and initial extinction performance was less in groups switched in drug state. The partial reinforcement extinction effect was present in Ss maintained on the drug, which forces a revision in the hypothesis that this drug directly reduces conditioned emotionality. (PsycINFO Database Record (c) 2006 APA, all rights reserved). © 1969 American Psychological Association.
