Weatherly, J. N., McSweeney, F. K., & Swindell, S. (1996).
Within-session response patterns on conjoint variable-interval variable-time schedules.
Journal of the Experimental Analysis of Behavior,
66, 205-218.
Operant responding often changes within sessions, even when
factors such as rate of reinforcement remain constant. The
present study was designed to determine whether within-session
response patterns are determined by the total number of
reinforcers delivered during the session or only by the
reinforcers earned by the operant response. Four rats pressed a
lever and 3 pigeons pecked a key for food reinforcers delivered
by a conjoint variable-interval variable-time schedule. The
overall rate of reinforcement of the conjoint schedule varied
across conditions 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 subjects received the same total
number of reinforcers by responding on simple variable-interval
schedules. Response patterns were less similar to those observed
on simple variable-interval schedules when the overall rate of
reinforcement exceeded 120 reinforcers per hour. These results
suggest that response-independent reinforcers can affect the
within-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., habituation) explanations.
Key words: within-session patterns,
variable-interval schedule, variable-time schedule, lever press,
key peck, rats, pigeons