Blocked and overshadowed stimuli are weakened in their ability to serve as blockers and second-order reinforcers in Pavlovian fear conditioning.
The ability of a blocked or overshadowed conditioned stimulus (CS) to serve as (a) blocker or (b) a 2nd-order reinforcer in Pavlovian fear conditioning was tested in 152 albino rats. CS-evoked suppression of barpressing for food was the index of conditioned fear. Experiments 1 and 2 showed that an overshadowed CS was weakened in its ability to serve as a blocker. In Experiment 2, a blocked CS was similarly weakened. Experiment 3 showed that an overshadowed and blocked CS was weakened in its ability to serve as a 2nd-order reinforcer. Experiments 4 and 5 failed to restore the blocking ability of blocked (Experiment 4) or overshadowed (Experiment 5) CSs by extinguishing the CSs that had blocked or overshadowed them. Results favor a learning-deficit view of blocking and overshadowing.
Rauhut
A S
AS
Department of Psychology, University of Massachusetts at Amherst 01003, USA.
McPhee
J E
JE
Ayres
J J
JJ
D000818:Animals; D001070:Appetitive Behavior; D001245:Association Learning; D001288:Attention; D003214:Conditioning, Classical; D005108:Extinction, Psychological; D005239:Fear; D005260:Female; D008297:Male; D051381:Rats; D012054:Reinforcement, Psychology