A classical conditioning situation was modified to make the US contingent on the nonoccurrence of the CR (anticipatory licking by rats). Ss did not learn the rewarded response. Classical conditioning of anticipatory licking developed in spite of a rapidly decreasing frequency of us presentations over conditioning sessions. F. D. Sheffield (1965) coined the term "omission training" to refer to a modified classical conditioning procedure in which the unconditioned stimulus (US) is withheld if an antiCipatory conditioned response (ACR) occurs, and is presented if the ACR does not occur. Sheffield designed the omission training technique as a test of the "reinforcement" (law-of-effect) interpretation of classical salivary conditioning in dogs. Although the general trend of his results fell against the reinforcement theory, Sheffield ran into difficulties with the long latency of the conditioned salivary response, and was not able to collect an adequate amount of clearly interpretable data.A number of recent studies (Miller, 1961;Patten & Deaux, 1966;Patten & Rudy, 1967) have reported classical conditioning of the licking response in rats. The licking ACR in rats is a very short latency response, and so was regarded as more suitable than salivation for employment in the omission training procedure. The present study employed the omission training procedure to -investigate the possibility that "reinforcement" (i.e., ACR-US contingency) controls the development of the ACR in rats.
MethodThe Ss were 12 naive female Wi star albino rats, 125-135 days old at the start of habituation to handling and deprivation, six of which were randomly assigned to each of two experimental groups.The apparatus was essentially the same as used in a previous study (Patten & Rudy, 1967) with the major exception that a compound CS (light plus tone) was used in the present study. Briefly, the response recording technique consisted of S's wearing a leather and stretch-nylon headgear which held an aluminum US delivery tube in place approximately 1/8 in. in front of S's mouth. A Hunter contact relay in series with an electric circuit through S detected each contact S's tongue made with the US tube.During conditioning sessions S was maintained on a 31 in. x 35 in. elevated platform. The only restraint on S's movement came from two contact wires and vinyl tubing through which the US reached the drinking tube. The wires and vinyl tubing were loosely suspended from above S to permit freedom of locomotor movement and to prevent S's becoming entangled in the wires.Licking was recorded for all Ss during a 3 sec period preceding CS-onset and, separately, during the first 3 sec of the CS, which consisted of a 550 cps, 35 dB tone and the light (.34 ft-c at 10 in.) from a darkened 15 W bulb. The CS bulb was centered on the edge of a long side of the platform. The US (.40 ml of a 15% sucrose solution) was delivered during the fourth second after CS-onset. For one group of six Ss (Group A), the CS terminated with US-offset; for the second group of six Ss (Gro...
Data from an experimental group and a pseudoconditioning control group show that licking responses in rats can be classically conditioned and that this conditioning occurs within 60 trials and extinguishes rapidly when water reinfore ement is removed.
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