Increase over Time in the Stimulus Generalization of Acquired Fear *

Following classical fear conditioning, Ss were trained to jump a hurdle to escape the fear-eliciting stimuli. 2 groups were conditioned in the start box of the hurdle apparatus (Same CB) and 2 in a separate, but similar, conditioning box (Diff CB). Under each condition, 1 group had hurdle training after a 3-min., and the other, after a 24-hr., postconditioning delay. For the 2 Diff CB groups, hurdle training involved a generalized stimulus situation. All groups, except Group 3 min.-Diff CB, learned to jump the hurdle in 25 trials. The significant improvement in performance with an increase in postconditioning delay under the Diff CB, but not under the Same CB, condition was attributed to an increase in the strength of the fear response over time to generalized, but not to the original, stimuli.