Latent stimulus control develops in extinction after very brief feature-negative, but not feature-positive, discrimination training in the runway

Abstract

Two groups of 10 rats each were briefly trained on a feature-discrimination learning problem in the runway. In Group FP, the feature was present on positive (S+) trials and absent on negative (S-) trials. The opposite arrangement held for Group FN. After 12 learning trials, 7 with S+ and 5 with S-, both groups received 10 extinction trials in a single session, 5 with S+ and 5 with S-. Neither group showed evidence of differential responding to S+ or S-in acquisition. In extinction, Group FN ran faster on S+ trials than on S-trials, an effect called latent discrimination learning. There was no evidence oflatent discrimination learning in Group FP. The results suggest that impaired FP performance in the runway, relative to FN performance, reflects retarded learning on the FP discrimination, rather than a performance deficit.Under some discrimination learning conditions, differential stimulus control by the positive (S+) and negative (S-) discriminative stimuli is not evident during discrimination training itself, yet it develops during a subsequent phase of extinction (Capaldi, 1979;Capaldi, Berg, & Morris, 1975;Hearst, 1987Hearst, , 1988. The emergence of differential response tendencies with respect to S+ and S-during an extinction test is called latent discrimination learning. Some of the reasons why discrimination learning may be latent have been discussed by Capaldi and Hearst and are not of immediate concern here. Rather, the present experiment capitalized on the fact that the procedures developed by Capaldi et al. (1975) provide a means of detecting differential control by S+ and S-after very brief runway discrimination training.The purpose of the present experiment was to assess the early development of differential stimulus control in a feature-discrimination learning problem in the runway. In this task, the discriminative cue is the presence versus absence of a distinctive stimulus (feature). In a go/no-go discrimination task in the runway, discriminative responding develops faster in the feature-negative (FN) condition, in which the feature is a component of S-, than in the feature-positive (FP) condition, in which the feature is a component of S+ (Haggbloom, 1983;Haggbloom & Sheppard, 1986). The faster rate of discrimination learning in the FN condition is called a feature-negative effect (FNE).In situations other than the runway-as, for example, those involving keypecking by pigeons in an operant 74 chamber-FP learning is invariably superior to FN learning, and, indeed, FN learning may completely fail to develop (see Hearst, 1978;Jenkins & Sainsbury, 1969). However, Hearst (1987Hearst ( , 1988 recently reported that discriminative responding that is absent or impaired during training on an FN problem will develop or improve during extinction. This latent FN discrimination learning reflects the acquisition of differential control by S+ and S-that was not evident in behavior during discrimination training.In the runway, the FP discrimination is eventually learned, and, given adequate training, performan...