The effects of punishment intensity on squirrel monkeys.
Responses of squirrel monkeys were maintained by a variable-interval schedule of food reinforcement. Concurrently, punishment consisting of a brief electric shock followed each response. As has been found for pigeons and rats, punishment did not produce extreme, all-or-none reactions. By gradually increasing the punishment intensity it was possible to produce response rates intermediate to no suppression and complete suppression. Similarly, the moment-to-moment response rate was free of extreme fluctuations. A "warm-up" effect occurred in which the punished responses were especially suppressed during the initial part of a session. The pre-punishment performance was negatively accelerated within a session, and punishment reduced the degree of negative acceleration. When punishment was discontinued, responding recovered immediately except when suppression had been complete or prolonged. When the punishment intensity was decreased gradually, more suppression resulted at a given intensity than when intensity was increased gradually. This suggests a "behavioral inertia" effect wherein behavior at a new punishment intensity is biased toward the behavior at the previous value. A corollary generalization is that the larger the change in intensity, the less the behavior at the new value will be biased toward the behavior at the previous value.