Abstract
Forty Wistar and 40 G-4 male rats had 7-hr. training on an operant avoidance schedule in which bar pressing delayed shock 20 sec. Each of 5 groups had a different warning stimulus condition 5 sec. before shock was due buzzer, light, random noise, 4,000-cps tone, and no-warning stimulus. On all performance measures and in both strains, the stimuli ranked in effectiveness from best to worst as follows: buzzer, light, noise, tone, no stimulus. G-4s received far fewer shocks than Wistars and differed from them in other measures.

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