Stimulus factors in aversive controls: conditioned suppression after equal training to two stimuli

Pigeons trained to peck a key for food were periodically presented with tones ending with electrical shock until tone presentation consistently suppressed ongoing pecks. Shock was then discontinued and gradients of stimulus generalization were assessed by presenting tones with frequencies above, below, and at the frequencies of those used to develop conditioned suppression. When the training tones had frequencies at 670 and 1500 cps, resulting gradients were bi-modal with peak suppression at 670 and 1500 cps. Of the other test tones, 1000 cps produced the most suppression. When the training tones had frequencies at 450 and 2250 cps, bi-modal gradients were again obtained with peak suppression to the 450 and 2250 cps tones. Of the other test tones, 1000 cps produced the least suppression. These results support the hypothesis that generalized response tendencies summate.     

The use of rats as discriminative stimuli

A FREE OPERANT PROCEDURE WAS USED TO DETERMINE WHETHER OR NOT ONE RAT COULD DISCRIMINATE: (1) between the presence and absence of a second rat, and (2) between two other rats of the same species and sex. The subjects were four male Wistar rats. The discriminatory response was a bar press and food was used as reinforcement during training. Although there were wide individual differences in rate of learning, all subjects learned to make both discriminations.