Four rats were exposed to an A-B-A-B series of 30 sessions each of variable-ratio 20 (A) and fixed-interval 30-s (B) schedules. Four other rats received 120 sessions of fixed-interval 30 s. The rats with a history of variable-ratio responding subsequently showed primarily high or low response-rate patterns on the fixed-interval schedule without evidence of classical scalloping (i.e., increased rates of responding throughout the interreinforcement interval), except infrequently in 1 rat. The rats exposed to only the fixed-interval 30-s schedule displayed the expected sequence of scalloping giving way to lower rate break-run or simply low-rate responding over time. This experiment shows that when naive rats are exposed to even a simple history of reinforcement (in this case, a variable-ratio 20), their subsequent fixed-interval performance is very different from comparable performance in naive rats, and might be said to be more similar to the responding of adult humans. The argument is made that care should be taken in comparing the fixed-interval performance of humans and nonhumans because humans have a complex history of reinforcement, whereas laboratory nonhumans are typically naive.

In two different discrete-trial procedures, pigeons were faced with choices between fixed-ratio and progressive-ratio schedules. The latter schedules entail diminishing returns, a feature analogous to foraging situations in the wild. In the first condition (no reset), subjects chose between a progressiveratio schedule that increased in increments of 20 throughout a session and a fixed-ratio schedule that was constant across blocks of sessions. The size of the fixed ratio was varied parametrically through an ascending and then a descending series. In the reset condition, the same fixed-ratio values were used, but each selection (and completion) of the fixed ratio reset the progressive-ratio schedule back to its minimal value. In the no-reset procedure, the pigeons tended to cease selecting the progressive ratio when it equaled or slightly exceeded the fixed-ratio value, whereas in reset, they chose the fixed ratio well in advance of that equality point. These results indicate sensitivity to molar as well as to molecular reinforcement rates, and those molar relationships are similar to predictions based on the marginal value theorem of optimal foraging theory (e.g., Charnov, 1976). However, although previous results with monkeys (Hineline & Sodetz, 1987) appeared to minimize responses per reinforcement, the present results corresponded more closely to predictions based on sums-of-reciprocals of distance from point of choice to each of the next four reinforcers. Results obtained by Hodos and Trumbule (1967) with chimpanzees in a similar procedure were intermediate between these two relationships. Variability of choices, as well as median choice points, differed between the reset and no-reset conditions. Although these differences are consistent with the relative costs (in responses per reinforcement) in the two procedures, the differing dispersions of choice probably arise mainly from differing structural constraints of the two procedures.

While a great deal of behavior analytic research has focussed on studying current contingencies, the amount ofwork done in the area ofconditioning history is spotty, at best. Weiner (1964Weiner ( , 1969 conducted history research with human subjects, but little has followed in either the human or the nonhuman literature. Some direction can also be found in the literature studying the effects of conditioning on drug effects (e.g., Barrett, 1977;Urbain, Poling, Millam, & Thompson, 1978). However, "behavioral history" or "conditioning history" has not been a fully-developed area within behavior analysis. It is suggested that empirical work on history effects might have implications for (a) better understanding humannonhuman behavioral differences and similarities, (b) clinical applications, especially where clients are resistant to behavioral change, and (c) theoretical assumptions in behavior analysis in relation to both basic and applied concerns.