Within-session changes in responding when rate and duration of reinforcement vary.

Three pigeons responded on variable interval 60-second and variable interval 30-second schedules. The duration of access to mixed grain was varied from 2-to 20-seconds per reinforcer in different conditions. Within-session patterns of responding did not differ when subjects received 2- versus 20-seconds access to the reinforcer for the schedule providing the lower rate of reinforcement. However, the within-session decreases in responding were steeper when reinforcers were 20-seconds than when they were 2-seconds for the schedule providing the higher rate of reinforcement. These results indicate that satiation is not necessary to produce within-session changes in responding, but it may contribute to those changes at high rates of reinforcement.