Abstract
Four dogs were given discriminative conditioning using 3 CSs. One CS (CS + C) was always reinforced with shock, another (CS−) was never reinforced while a third (CS + U) was reinforced 75% of the trials with reinforcement occurring either immediately, 2 or 4 sec. after the termination of CS. Heart-rate change was greater for CS + C than for CS + U or CS there was no significant difference between the latter. The termination of the CS + U appeared to be informative; mean heart rate during the post-CS period on unreinforced trials of CS + U was not significantly different from that during CS + C. Flexion latencies were longer to CS + U. The cardiac UR was less for CS + U than for CS + C, suggesting that temporal uncertainty inhibits the UR.
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