WITHIN-SESSION PATTERNS OF RESPONDING WHEN THE OPERANDUM CHANGES DURING THE SESSION

Eight pigeons and 10 rats responded on variable interval I-min or vari able interval 30-s schedules. During baseline, the same operandum prod uced reinforcers throughout the session. During the switch conditions, performing one response produced reinforcers early in the session and performing a different response produced reinforcers later. The switc h between the two responses occurred 10, 20, 30, or 40 min into the se ssion in different conditions. Within-session patterns of responding w ere not usually different when the same operandum produced reinforcers throughout the session and when the operandum changed from the right to the left key (pigeons) or lever (rats). Changes from a treadle to a key (pigeons) or from a lever to a key (rats) also failed to alter wi thin-session patterns of responding. These results suggest that factor s related to the form of the instrumental response (e.g., muscular war m-up, fatigue) contributed little to within-session changes in respond ing under the present circumstances. (C) 1995 Academic Press,Inc.