Response-duration of lever pressing in the rat

Two aspects of the lever-holding behaviour of rats in a Skinner-box have been analysed: firstly, the changes in the duration of the responses during the acquisition and experimental extinction phase, and, secondly, the bunching of responses during the experimental extinction phase. The response-durations on the first few acquisition trials were found to be bimodally distributed, but to become stabilized at 0.42 seconds as practice increased. During experimental extinction response-durations increased. The rate of increase depended on the conditions of secondary reward. Rats who had the source of secondary reward removed, or restricted, yielded a steeper slope than those who responded under the same conditions of secondary reward as during training.

The analysis of the extinction scores revealed that unrewarded responses were emitted in groups. Response-group latencies were shown to progress as a positive function of the number of response-groups, and the average response-duration for consecutive response-groups to increase progressively. The slope of the duration curve plotted for successive response-groups increased, and this was related to an increase in the value of the time-intercept for successive response-groups.