Vocal and nonvocal discriminative performance in monkeys

Discriminative performance of a lever press and a vocal call was compared in five macaques. The animals exhibited similar scores for Response Rate, Efficiency, and Error Index. Total vocal responses were slightly higher than total lever responses. Latency for vocal responses was significantly greater than lever press. Similar scores in measures of performance of the two behaviors indicate that discriminative vocalization is not exceedingly difficult. Failure by others to achieve discriminative vocalization in studies employing weak positive-reinforcement contingencies suggest that certain experimental paradigms are unsatisfactory for vocal conditioning.