Fear conditioning as a function of CS duration during acquisition and suppression tests

Abstract

The effects of CS duration during fear conditioning were assessed using a secondary punishing technique. CS duration was not found to be an influencing variable. Inadequacies of the secondary punishment procedure utilized by Mowrer and his colleagues were noted and it was suggested that more ex­ tensive comparisons be made of the CER technique with an improved secondary punishing procedure. In investigating critical parameters of fear condi­ tioning, Mowrer & Aiken (1954) and Mowrer & Solomon (1954) used the technique of conditioned suppression via a secondary punisher. In this procedure a rat is trained to make an operantbarpressona CRF schedule for food. Concurrently, but in a different environment, a CS (light) is presented immediately prior to shock, i.e., a fear conditioning procedure. After several training sessions in each situation, the CS is used as a secondary punisher by being made contingent on the bar press. The fear arousing capacity of the light is inferred from the amount of response suppression which occurs during the secondary punishment phase. This procedure differs from the more widely used conditioned emotion response (CER) procedure (Estes & Skinner, 1941) in that in the CER technique the presen­ tation of feared stimulus is not contingent upon S's re­ sponse. It is programmed independently of the food rein­ forcement schedule. The amount of response suppres­ sion which occurs while the conditioned stimulus is pres­ ent is taken as an index of its fear arousing capacity. Kimble (1961, p. 270) states that ... the function relating strength of fear to the time separating neutral and noxious stimuli resembles thatfor other classically conditioned responses. However, this generalization has a very limited empirical support being based pri­ marily on studies of avoidance conditioning rather than fear conditioning per se. Those experiments which have studied fear conditioning using a CER procedure have typically found optimal durations to be considerably longer than the .5 sec. which Kimble implies. Libby (1951) found that response suppression increased with increases in CS duration up to 7 sec., but observed no increases between 7 sec. and 30 sec., i.e., the function was a negatively accelerated increasing one which was asymptotic around 7 sec. Using pigeons, Lyon (1963) found that as the CS duration increased from 100 to 300 sec., the amount of suppression increased. Simi­ larly, Stein et al (1958) and Carlton & Didamo (1960) found relative CS duration to be an important parameter of conditioned suppression. The purpose of the present experiment was to de­ termine if similar results would be obtained if the CS