Aparicio, C.F. & Baum, W.M. (2006).
Fix and sample with rats in the dynamics of choice.
Journal of the Experimental Analysis of Behavior, 86, 43-63.
The generality of the molar view of behavior was extended to the study of
choice with rats, showing the usefulness of studying order at various levels
of extendedness. Rats’ presses on two levers produced food according to
concurrent variable-interval variable-interval schedules. Seven different
reinforcer ratios were arranged within each session, without cues identifying
them, and separated by blackouts. To alternate between levers, rats pressed on
a third changeover lever. Choice changed rapidly with changes in component
reinforcer ratio, and more presses occurred on the lever with the higher
reinforcer rate. With continuing reinforcers, choice shifted progressively
in the direction of the reinforced lever, but shifted more slowly with each
new reinforcer. Sensitivity to reinforcer ratio, as estimated by the generalized
matching law, reached an average of 0.9 and exceeded that documented in previous
studies with pigeons. Visits to the more-reinforced lever preceded by a reinforcer
from that lever increased in duration, while all visits to the less-reinforced lever
decreased in duration. Thus, the rats’ performances moved faster toward fix and
sample than did pigeons’ performances in previous studies. Analysis of the effects
of sequences of reinforcer sources indicated that sequences of five to seven
reinforcers might have sufficed for studying local effects of reinforcers with
rats. This study supports the idea that reinforcer sequences control choice between
reinforcers, pulses in preference, and visits following reinforcers.
Key words: choice, molar view, visits patterns, fix and sample, lever press, rats