Fixed-ratio schedule-induced aggression.

Pigeons' pecks were conditioned with food reinforcement. Subjects were exposed to sessions of no-reinforcement and of fixed-ratio reinforcement. The pigeons attacked a target animal during the fixed-ratio reinforcement conditions. The attack occurred primarily during the post-reinforcement pause and occurred after almost every instance of reinforcement. Little or no aggressive behavior was demonstrated during periods of no-reinforcement except on the initial days of these conditions. The results indicated that a fixed-ratio schedule of reinforcement has certain characteristics capable of producing aggression.