Influence of facial expressions on the classical conditioning of fear.

Previous research has demonstrated that particular facial expressions more readily acquire excitatory strength when paired with a congruent unconditioned stimulus than when paired with an incongruent outcome. The present study extends these findings on the excitatory and inhibitory role of facial expressions by demonstrating that particular facial expressions (fear and happy), when paired with a neutral cue (tone), can influence conditioning to the neutral conditioned stimulus (CS). It was found that subjects who had a fear expression paired with the neutral CS responded more to the fear expression than to the neutral CS, whereas subjects who had a happy expression paired with the neutral CS responded more to the neutral cue than to the happy expression. These findings strongly support predictions from "overshadowing" or "blocking" models of classical conditioning.