A new testing package, including apparatus and tasks, is described for the study of behavior of a variety of species in a variety of experiments. The package is described with respect to the kinds of comparative psychological investigations for which it is well suited. The preliminary data generated within this new testing paradigm demonstrate that the NASA/LRC Computerized Test System provides a flexible yet powerful environment for the investigation of behavioral and psychological processes.

In this experiment, a chimpanzee's (Pan troglodytes) long-term retention was examined. The chimpanzee, Lana, was trained to use lexigrams (geometric symbols representing linguistic units) for foods, colors, and objects when she was 2 years of age. At the age of 27, her recognition of three sets of lexigrams was examined. One of these sets (long term lexigrams) included five object lexigrams, one color lexigram, and one food lexigram, none of which had been seen by Lana for more than 20 years. The second set (different-referent lexigrams) contained lexigrams that are still present on current lexigram keyboards, but had been assigned new referents. The third set (same-referent lexigrams) contained lexigrams that had been kept on the keyboards Lana had used and that had retained the same referents. A food, a colored square, or an object was presented, and Lana had to select, by using ajoystick, a lexigram on a computer screen. Lana chose the correct lexigram at a level significantly greater than chance for five of the seven lexigrarns that she had not seen for more than 20 years.Human subjects can retain information for variable lengths oftime. They can retain, over a period of months and even years, course schedules and word lists

The effect of the size of the floor area of the operant test chamber on behavior was tested using a standard-size test chamber and a test chamber with one-fourth of the floor area of the standard chamber. Two groups of pigeons were tested under a differential-reinforcement-of-low-rate 15-sec schedule or a variable-interval 60-sec schedule. Both groups of pigeons had higher response rates while in the smaller floor area. Pigeons under the differential-reinforcement-of-low-rate schedule also showed a decrease in rate of reinforcement, an increase in ratio of responses to reinforcements, and an alteration in interresponse-time-per-opportunity distributions when tested in the reduced floor-area condition. These effects are similar to those found under physical restraint, indicating that amount of floor space available for locomotion interacts with schedule behavior and that physical restraint may be regarded as the lower limiting value of amount of floor area available for locomotion.

Pigeons pecked a key and rats pressed a lever for food reinforcement under large values of the differential‐reinforcement‐of‐low‐rate schedule. Each subject was tested under 10 different schedule values ranging from 1 to 45 min and was exposed to each schedule value at least twice. The mean interresponse time and mean interreinforcement time increased with the schedule value according to power functions. Response‐probability functions were computed for schedule values below 20 min and showed an increase in response probability as a function of time since the last response in most cases. Mean responses per reinforcer increased as a function of schedule value for the rats, but decreased as a function of schedule value for the pigeons. The proportion of responses with interresponse times shorter than 1 sec were an increasing function of schedule value for the pigeons, but did not vary as a function of schedule value for the rats.

Pigeons and rats wvere used in a yoked-control design that equated the reinforcement distributions of differential-reinforcemiient-of-lowv-rate and variable-interval schedules. Both a between-subjects design and a wvithin-subjects design found response rate higher for the variable-interval schedule than for the differential-reinforcemiient-of-lowv-rate schedule, thus delnionstrating the effcctiveness of the differential-reinforceiiient-of-low-rate contingency.The interresponse-time distributions were unimodal for all subjects under the variableinterval schedule and bimodal for pigeons under the differential-reinforcement-of-low-rate schedule. The interresponse-time distributions for rats under the differential-reinforcemiientof-low-rate schedule wvere also bimodal in three of four cases but the height of the modes at the shorter interresponse times were snmall in both absolute value and in relation to the height of the miodes at the shorter interresponse times of the pigeons' distributions.The reinforcement contingency of the differential-reinforcement-of-low-rate (DRL) schedule specifies differential reinforcement of interresponse times (IRTs). Any response terminating an IRT longer than the value specified by the DRL sclhedule is reinforced; any response terminating an IRT shorter than the value specified by the DRL sclhedule is not reinforced. As the name of this sclhedule implies, the reinforcement contingency that exists under the DRL schedule is expected to produce a low response rate. However, a low response rate alone is not proof of the effectiveness of the DRL reinforcement contingency. In responses will meet the DRL requirement and will be reinforced, while other responses, not meeting the DRL requirement, will not be reinforced. As the DRL value is increased, two marked effects occur; the rate of reinforcement and the rate of responding decrease (Staddon, 1965). However, these same relations exist for the variable-interval (VI) schedule, which makes reinforcement available for the first response that occurs after a specified time has elapsed. This specified time is measured from the preceding reinforcement or some other environmental event and varies in length from reinforcement to reinforcement. As the value of the VI schedule is increased, there is a decrease in rate of reinforcement and rate of responding (Catania and Reynolds, 1968). This leaves the possibility that the rate of responding maintained by a DRL schedule is due only to the rate of reinforcement and the distribution of reinforcement in time. It is possible that the differential reinforcement of IRTs specified by the DRL schedule has no direct effect on behavior, i.e., the subject is effectively on a VI schedule.An experimental design that equates rate of reinforcement and interreinforcement times for a subject under a DRL schedule and a VI schedule is necessary if the effectiveness of the DRL schedule is to be empirically tested. The yoked-control design with the lead subject under a DRL schedule and the yoked-control subject under ...