Harry M. B. Hurwitz

Extinction and maintenance of avoidance behavior using response-independent shocks

Response-independent shocks were delivered to six Ss previously trained to avoid shock. The response rate failed to recover when shocks were administered immediately following an avoidance-extinction procedure. The avoidance response rate was reinstated when shocks were presented 24 h after extinction. A second experiment involving six Ss demonstrated that when the avoidance session was immediately followed by response-independent shocks, the avoidance response rate was maintained.

Concurrent Performance in Septally Operated Rats: One and Two Response Extinction'

Abstract In Experiment I, five male hooded rats underwent surgery for septal lesions and were tested in procedures in which two responses were concurrently reinforced. It was found that septally operated animals responded at higher rates for sucrose reinforcement than did controls. When reinforcement was withdrawn for both concurrent responses, the septal animals continued to respond at a higher level than controls. When reinforcement was withdrawn for one of the concurrent responses, but maintained on the other, septal animals suppressed levels of nonreinforced responding as quickly as controls. These results were replicated in a second experiment on nine septally operated animals and with water reinforcement instead of sucrose. Operant response levels taken in this experiment showed that septals responded at significantly higher operant levels than controls. The importance of the high septal operant and reinforced response rates for the extinction data is discussed.

Response Specification and Acquisition of Free Operant Avoidance Behavior

In Exp. 1, 2 groups of rats were trained under a free operant avoidance schedule. The response was a press on a lever for Group BP (18 subjects) and a release of the lever for Group EP (22 subjects). Neither the rate of response nor the frequency of shock discriminated between the two groups, but there was a slight difference in the lever-holding time. In Exp. 2, 3 subjects were trained for 35 2-hr. sessions. In addition to the measures used in Exp. 1, a measure of avoidance proficiency (AVPRO) was employed. It was shown that (1) substantial improvement in avoidance developed late in training; (2) that AVPRO was correlated with changes in lever-holding behavior and was poorly related to the rate of response.

Rates of concurrent responses and reinforcer duration

Rats were rewarded concurrently, at equal frequencies, for pushes at the doors in front of two reinforcement magazines. The duration of the reinforcer given at one magazine was constant, while the reinforcer duration at the other magazine was changed every six sessions. For three rats the constant reinforcer was 3 sec, and for three other rats the constant reinforcer was 1 sec. For all these animals the duration of the alternative reinforcer was varied between 1 and 5 sec. Rate of response at the magazine that delivered the constant reinforcer duration was found to vary inversely with the duration of the reinforcer obtained at the alternative magazine. The matching of relative response rate to relative reinforcer duration was poor, and the results are attributed partly to the general rate-suppressing effects of long reinforcer durations.

Effects of relative reinforcer duration on concurrent response rates

For three rats, responses on two bars were reinforced equally often, but with different reinforcer durations, on a variable interval schedule. With only one reinforcer being changed at a time, five pairs of reinforcer durations were tested in exposures of between 9 and 30 sessions. When a reinforcer duration was changed, the rates of both responses usually altered gradually, suggesting that the absolute rate of a response was controlled by the relative duration of its reinforcer. The relative rate of a response (the rate of one response divided by the sum of both response rates) was a linear function of the relative duration of its reinforcer. for the three values tested.

Extinction of free-operant avoidance with and without feedback

Extinction of free-operant avoidance behavior of rats was studied under conditions in which a response either resulted in a response-contingent event (feedback) or had no scheduled consequence. Probes and the original conditions of training were alternated. The time to reach the criterion of extinction and the number of responses in extinction were greater when a feedback stimulus was available. Cyclic patterns of responding were observed during both free-operant avoidance and extinction.

The effect of septal lesions in rats on performance of a free-operant avoidance task ☆

Abstract Twenty female hooded rats of the Long-Evans strain served in a study of the effects of septal lesions on free-operant avoidance performance. Although there was no statistically significant difference between septal damaged and normal rats on responses emitted or shocks received, it was shown that normal animals emitted more responses than septal preparations in four second intervals following shock. Results are interpreted as demonstrating that shock is more disruptive to the bar-press response for septal damaged animals, and that this factor could partially account for the prevously reported different IRT distributions generated by septal damaged and normal animals on similar free operant avoidance tasks.

The Effects of the Warning Signal on Response Characteristics in Avoidance Learning

Two experiments are reported in which a buzz was used to indicate either the inter-trial interval (ITIBUZZ) or the warning period (WARNBUZZ) in a discriminated avoidance schedule (Experiment 1) or to indicate the beginning only of these periods (FEEDBUZZ and TRACEBUZZ, respectively) (Experiment 2). 11 hooded rats served as Ss. Faster acquisition of the lever press avoidance response was obtained when the buzz was associated with either the beginning or with the entire warning period than when this stimulus was associated with the beginning or with the entire inter-trial interval. The results were related to topographical characteristics of the lever response. During early taining sessions, Ss learned to escape shock and concurrently developed extensive lever holding. It was observed that onset of the buzz interfered with lever holding so that its use as a warning signal, as in WARNBUZZ and TRACEBUZZ conditions, promoted momentary release of the lever and thus favored avoidance acquisition.

Progressive Ratio Performance with Reset Option

Lever responses of rats were reinforced under progressive ratio schedules where the response requirement increased after each reinforcement. The ratio could be reset to its initial value by an alternative response. Systematic relations were found between the size of the progressive ratio schedule and the frequency of the reset responses. The procedure facilitated an analysis of the interaction of effort and time variables which were reflected in the sequential properties of the responses.

The effect of constant current shock intensities on the acquisition of a discriminated avoidance response

Twenty-seven naive female hooded rats were trained in a lever-pressing situation under a discriminated avoidance procedure in a single 4 hr. session. Different groups received 0.8, 1.6 and 2.8 ma of constant current shock. Analysis of the results showed a slight advantage for Ss trained with a low constant current.