Reinforced variability in rats: effects of gender, age and contingency.

Operant variability was compared in four groups of Long-Evans rats (young males, young females, mature males and mature females) under two different conditions. Under VAR contingencies, where response variability was required for reinforcement, a sequence of four responses on left (L) and right (R) levers had to differ from each of the preceding four sequences. If LLLL, LRLL, RRRR, and RRLL had just occurred, then a RLRL sequence, for example, would be reinforced in the next trial, but LRLL would not. Sequence variability was compared to that under YOKE contingencies, where reinforcement was provided whether or not the rats varied their responses. We found that young rats behaved more variably than mature rats, this effect most pronounced under the YOKE contingencies, where variability was not required. On the other hand, variability was not related to gender under either VAR or YOKE conditions. Thirdly, all groups were sensitive to the schedule contingencies, behaving more variably under VAR than under YOKE. Thus age and schedule requirements influenced operant variability, but gender did not.