Strength of fear as a function of the number of acquisition and extinction trials.

Abstract

Experiment was designed to (a) determine the relation between strength of fear and varying numbers of acquisition trials, and (b) investigate the extinction of fear under conditions in which no new response is learned during extinction. A total of 138 hooded female test rats and a control group of 10 were run in a factorial study in which the exptl. variables were (a) number of fear-acquisition trials (1, 3, 9, and 27), and (b) number of fear-extinction trials (0, 3, 9, and 27). All rats went through exptl. phases which involved acquisition of fear (paired presentations of CS and shock), extinction of fear (CS without shock), and acquisition of hurdle-jumping. During the hurdle-jumping trials the CS was presented without shock and subjects were permitted to jump a hurdle and enter a 2d compartment. After this response was completed the CS was terminated. The latency of hurdle-jumping response was measured. A backward conditioning procedure was employed for the control group to control for possible sensitization effects. It was concluded that the exptl. variables had a significant effect upon the acquisition of hurdle-jumping and that fear increases as a monotonic function of number of fear-conditioning trials and weakens progressively with successive extinction trials.