A study of the temporal factors in the fear conditioning in the albino rat

Abstract

Libby (6) studied the temporal factors which worked at the acquisition of Estes-Skinner type conditioning. He found that the depressant effect was maximum in 710 sec. intervals between the onset of the CS (light) and the onset of the US (aversive stimulus). The present study was designed to reexamine the Libby's results by using the procedure of Mowrer (7) and analyzed the factors acted in the fear-conditioning.Subjects : 42 albino rats (25 males and 17 females) were used.Apparatus : Skinner-box which had a grid floor.Procedure : After 3 day bar-pressing training, Ss were divided into five experimental and one control groups. The experimental groups E1, E4, E7, E10, and E20 had CS (blinking light) -US (0.35 mA, A C) pairing with 1, 4, 7, 10and 20 sec. interval each. The length of the US was 3 sec. and both stimuli turned off at the same instant. In the course of the five days of training period, Ss made 60 trials reinforced bar pressing responses, and had the total of 7 fear-conditioning. Control group was given only US without CS. Test trials were made as follows : Test P : After the Ss reached the criterion of the operant level, they were allowed to bar-pressing responses for five min. in dark.Test L : Each Ss continued to bar-press for one min. with CS.Test D : Each Ss continued to bar-press for one min. in dark. Test L & D were alternately repeated five times, one min. each, so the total of the L-D test was ten min.Results : 1) The mean numbers of responses in Test L (Table 1) and the inflexion ratio (I) indicated that the depression is maximum at the 7-sec. CS-US interval. (Fig. 2 & Table 2) 2) In Test L, the recoveries from depression were greater in E1 and E20 than E4, E7, and E10, especially in E10, almost all behavioral patterns were depressed and the responses in Test D were also decreased (Fig. 1).3) The CS effects were not seen in the control group.Conclusion : 1) Depressant effect was the greatest around 7-sec. interval and decreased monotonously in both sides. These results coincided with Libby's in greater parts.2) By this new method the characteristics of foregoing experiments which are important to investigate the nature of fear have been cleared to some degree.