THE EFFECTS OF SHOCK INTENSITY ON CLASSICAL DISCRIMINATION CONDITIONING OF THE HEART RATE IN RABBIT

A 2 by 2 factorial design used two different shock intensities of 6 and 14 ma and two different conditions of shock intensity control (constant and gradual increase). In the first condition the shock intensity was set at either 6 or 14 ma and maintained at that value for 10 days of classical discrimination conditioning. In the second condition the shock intensity was gradually increased from 2 ma to either 6 or 14 ma over a period of days and then maintained at that level for additional 10 days of training. The Ss were 40 New Zealand albino rabbits and were randomly assigned to 1 of 4 groups of 10 Ss each. During each daily session, Ss received 24 trials with the CS+ and 24 trials with the CS- randomly presented. The HR-CRs were assessed only on test trials by measuring the distance between 10 successive heart beats prior to CS onset and comparing this with the measurement of 10 successive heart beats immediately following CS onset. The results of this experiment demonstrated that the different conditions of shock intensity control led to the different HR responses. The constant shock group showed significantly larger deceleratory HR responses initially, but decreasing more rapidly than the gradual increase group. However, no significant difference of HR responding between the two different shock intensities in either acquisition or discrimination was found in this experiment.