Peter Harzem

Determinants of operant behaviour in humans: Some differences from animals

The performance of human subjects was investigated on fixed-interval (FI) schedules of reinforcement where responses meeting the schedule requirement produced points, later exchanged for money. For one group (the conventional FI condition) presses on a single response-panel were reinforced according to an FI schedule. For another group the procedure was the same as in the conventional FI condition, except that each response also illuminated a digital clock for 0.5 s. A third group responded on two panels; presses on one panel produced reinforcement on an FI schedule, and presses on the second panel illuminated the digital clock for 0.5 s. Responding in the conventional FI condition varied considerably both within and between subjects and different response measures showed no systematic relationship with FI value. For subjects in the other two groups, the pattern of responding on the clock-illuminating panel was scalloped, showing a pause after reinforcement followed by an accelerated response rate; the post-reinforcement pause was an increasing function, and running rate (calculated after excluding the post-reinforcement pause) was a decreasing function, of the value of the FI schedule. The data were compared with results of animal studies on FI schedules and some of the factors which affect performance on these schedules were analysed.

After-effects of reinforcement magnitude: Dependence upon context

On a fixed-interval schedule with rat subjects the duration of the post-reinforcement pause was found to be an increasing function of the magnitude of the preceding reinforcer. This relationship was observed when two magnitudes were contrasted closely in time, but not when the subjects were trained on each magnitude until the establishment of stable responding. After the behaviour was stable, the effect of the magnitude of reinforcement re-emerged when 50% of the scheduled reinforcers were omitted. Thus, the positive relationship between the magnitude of reinforcement and the duration of the post-reinforcement pause depended on the context of presentation of a given magnitude.

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.

After-Effects Of Reinforcement Magnitude On Temporally Spaced Responding

Rats were trained on two-component DRL schedules. In testing, a different concentration of liquid reinforcer was used in each session. The main effects were on the interresponse times initiated by reinforced responses. The median duration of these interresponse times and the rate of reinforcement increased as functions of reinforcer concentration. There was a corresponding increase in the efficiency of performance. These effects were attributed to the inhibiting after-effect of the reinforcer, rather than to an increase in the temporal accuracy of performance.

Social Interactions of a Group of Severely Retarded People with Staff and Peers in a Ward Setting

The social interactions of 13 severely retarded persons were observed with each other and with staff, in a small hospital. There were marked individual differences in susceptibility to social interaction. The frequency of peer interaction was very low. In terms of interaction with the staff, the subjects could be grouped as high, moderate and low scorers. Aversive behavior, such as hitting and scratching, was emitted spontaneously by some high scorers thereby achieving interaction from staff, and by the low scorers, in response to approaches from the staff, thereby decreasing the likelihood of such attempts at interaction.

The Aftereffects of Reinforcement Magnitude and Stimulus Intensity

Rats were trained on a fixed-interval schedule where each interval had an equal probability of being terminated by reinforcement or by an auditory stimulus. In testing, the concentration of the milk reinforcer and the intensity of the sound were varied. The durations of both the postreinforcement and the poststimulus pauses were found to be increasing functions of reinforcer magnitude and stimulus intensity, respectively. It is suggested that the effect of changes in the reinforcer magnitude upon the duration of the postreinforcement pause reflects the enhancement or impairment of the discriminative function of the reinforcer in the same way that the discriminative function of any stimulus may be affected by changes in its intensity.