McSweeney, F. K., Swindell, S., & Weatherly, J. N. (1996).
Within-session changes in responding during concurrent schedules with different reinforcers in the components.
Journal of the Experimental Analysis of Behavior,
66, 369-390.
Rats and pigeons responded on several concurrent schedules that
provided different reinforcers in the two components (food and
water for rats, Experiment 1; wheat and mixed grain for pigeons,
Experiment 2). The rate of responding and the time spent
responding on each component usually changed within the session.
The within-session changes in response rates and time spent
responding usually followed different patterns for the two
components of a concurrent schedule. For most subjects, the bias
and sensitivity to reinforcement parameters of the generalized
matching law, as well as the percentage of the variance accounted
for, decreased within the session. Negative sensitivity
parameters were sometimes found late in the session for the
concurrent food-water schedules. These results imply that
within-session changes in responding could cause problems for
assessing the validity of quantitative theories of
concurrent-schedule responding when the components provide
different reinforcers. They question changes in a general
motivational state, such as arousal, as a complete explanation
for within-session changes in responding. The results are
compatible with satiation for, or sensitization-habituation to,
the reinforcers as explanations.
Key words: concurrent schedule, within-session patterns of
responding, matching law, lever press, key peck, rats, pigeons