WITHIN-SESSION RESPONSE PATTERNS ON CONJOINT VARIABLE-INTERVAL VARIABLE-TIME SCHEDULES

Operant responding often changes within sessions, even when factors su ch as rate of reinforcement remain constant. The present study was des igned to determine whether within-session response patterns are determ ined by the total number of reinforcers delivered during the session o r only by the reinforcers earned by the operant response. Four rats pr essed a lever and 3 pigeons pecked a key for food reinforcers delivere d by a conjoint variable-interval variable-time schedule. The overall rate of reinforcement of the conjoint schedule varied across condition s from 15 to 480 reinforcers per hour. When fewer than 120 reinforcers were delivered per hour, the within-session patterns of responding on conjoint schedules were similar to those previously observed when sub jects received the same total number of reinforcers by responding on s imple variable-interval schedules. Response patterns were less similar to those observed on simple variable-interval schedules when the over all rate of reinforcement exceeded 120 reinforcers per hour. These res ults suggest that response-independent reinforcers can affect the with in-session pattern of responding on a response-dependent schedule. The results are incompatible with a response-based explanation of within- session changes in responding (e.g., fatigue), but are consistent with both reinforcer-based (e.g., satiation) and stimulus-based (e.g., hab ituation) explanations.