DAILY RHYTHMS IN A COMPLEX OPERANT - TARGETED PERCENTILE SHAPING OF RUN LENGTHS IN RATS

Daily rhythms in response output and accuracy were examined when reinf orcement for a complex operant was uncoupled from accuracy of performa nce. Rats housed in operant conditioning chambers earned their daily r ation of food under a targeted percentile procedure for responding on two levers. The targeted pattern was a series of consecutive responses on the left lever (a ''run''), followed by a single response on the r ight lever. The targeted run length was either ''0'' (i.e., undefined, under the nondifferential baseline), 6, 12 or 24. Under baseline, a r andom third of all trials ended in pellet delivery; under the percenti le conditions, trials with runs closer to the target than two-thirds o f the runs from the most recent 24 trials ended in pellet delivery. Th is contingency shaped run lengths while ensuring that approximately on e-third of all trials produced pellets. Responding tracked the target value well, with mean obtained run lengths equal to 90% of the target or better. Daily rhythms were clearly evident in measures of overall o utput, with subjects responding primarily 3-7 h into the dark period. The only substantial light-period responding observed in all subjects occurred during the 2 h after noon, when the chambers were serviced. N o systematic variation in this pattern was observed as a function of t arget. Run length was much less variable across the daily cycle than w as response output, with only a suggestion under the longest target th at response accuracy was lower during periods removed from the period of peak activity. (C) 1997 Elsevier Science Inc.