2 studies monitored with an independent measure fear of the CS during acquisition and extinction of a shuttle-box avoidance response by rats. Rats were first trained to bar press in a Skinner box, then subgroups were trained to various criteria of acquisition and extinction of avoidance; finally the suppressant effect of CS presentation in the Skinner box was observed. The technique yielded a monotonic function relating fear of the CS to number of CS-US pairings. Prolonged extinction training of the avoidance response was associated with decreased fear of the CS, but Ss trained to a moderate extinction criterion were very fearful of the CS. The function relating fear to avoidance acquisition criterion was U shaped.

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