Resistance to change of operant variation and repetition

A Multiple chained Schedule was used to compare the relative resistance to change of variable and fixed four-peck response sequences in pigeons. In on e terminal link, a response sequence produced food only if it occurred infr equently relative to 15 other response sequences (vary). In the other termi nal link, a single response sequence produced food (repeat). Identical vari able-interval schedules operated in the initial links. During baseline, low er response rates generally occurred in the vary initial link, and similar response and reinforcement rates occurred in each terminal link. Resistance of responding to prefeeding and three rates of response-independent food d elivered during the intercomponent intervals then was compared between comp onents. During each disruption condition, initial- and terminal-link respon se rates generally were more resistant in the vary component than in the re peat component. During the response-independent food conditions, terminal-l ink response rates were more resistant than initial-link response rates in each component, but this did not occur during prefeeding. Variation (in var y) and repetition (in repeat) both decreased during the response-independen t food conditions in the respective components, but with relatively greater disruption in repeat. These results extend earlier findings demonstrating that operant variation is more resistant to disruption than is operant repe tition and suggest that theories of response strength, such as behavioral m omentum theory, must consider factors other than reinforcement rate. The im plications of the results for understanding operant response classes are di scussed.