A comparison of an intermittent versus continuous CS in classical conditioning of the nictitating membrane response of the rabbit

Abstract

Thirty four Ss were randomly assigned to two groups conditioned to either an 1100 msec. continuous CS tone (N = 17) or an intermittent, 50 msec. on and 50 msec.off, CS tone of 1100 msec. duration (N = 17). Higher levels of conditioning were obtained in the pulsed CS group and the relevance of this finding to the stimulus trace hypothesis was discussed. ProhlemIn Pavlov's studies of classical conditioning (Pavlov, 1927) extensive use was made of intermittent CSs (e.g., rotating discs, metronome, bubbling water). Although a direct comparison of the relative efficacy of an intermittent vs. continuous CS on the course of conditioning has not been made, it might be expected that intermj.ttent stimuli would produce a greater number of afferent firings. According to Pavlov the strength of conditioning depends upon the intensity of the afferent state of affairs existing at the time of US onset. Hull (1943Hull ( , 1952 also postulated that strength of conditioning is a function of the intensity of the trace present at the time of US occurrence; and Anderson (1960) reformulating the stimulus trace concept within the framework of statistical learning theory, made the similar suggestion that strength of conditioning is a function of the number of active CS elements coincident with US onset. Consequently, the stimulus trace hypothesis would lead to the prediction that an intermittent CS produces a higher level of conditioning than a continuous CS. The present investigation was concerned with making such a comparison. MethodThe apparatus and preparation employed in conditioning the nictitating membrane of the rabbit have been described in detail (Gormezano, 1964;Schneiderman & Gormezano, 1964). Briefly, S was placed ina Plexiglass restraining box with his head inserted through an adjustable stock comprising the front of the box. Gross head movements were further reduced by fastening the pinna of both of Ss ears to the front of the stock with a foam rubber coated clamp. A muzzle-like assembly containing a stimulus air jet and rotary potentiometer was mounted on the animal's head. To permit recording of membrane movement and to insure continual exposure of the cornea, the superior and inferior eyelids of S's right eye were held back by means of stainless steel clasps. A silk thread was attached to a rod mechanically coupled to the shaft of the potentiometer and a smallmetal hook connected to the other end of the silk thread was attached to a nylon loop sutured in the nictitating membrane of S's right eye. The signals from the potentiometer, genera ted by movement of the membrane, were amplified and recorded by means of an Offner Dynograph.Thirty four albino rabbits, 80-100 days old, were randomly assigned to either a Continuous CS group (N = 17) wherein the CS consisted of a 1000 cps tone having an intensity of 76 db (relative to .0002 dynes/ cm 2 ) or to an Intermittent CS group (N = 17) conditioned to the same tone, except that the tone was repetitively interrupted, 50 msec. on and 50 msec. off, to produce a discont...

Single session conditioning of the nictitating membrane in the rabbit: Effect of intertriai interval

“…to 1 min. (Papsdorf et a!., 1964). In order to obtain conditioning in a single session in the present study, two steps were taken to increase the rate of acquisition of the conditioned response.…”