Stimulus generalization and stimulus discriminability: effects of perphenazine.

Abstract

The relationship between stimulus generalization and stimulus discriminability, in human Ss, has been investigated at several poinrs along the dimension of visible wavelength (2). This latter study by Kalish was intended as an empirical verification of several predictions which follow from the assumption of an inverse relationship between generalizacion and discrimination. Specifically, this hypothesis proposes that stimulus generalization occurs to the extent to which the organism is unable to discriminate berween a standard stimulus (SS) and ocher similar stimuli (GSs) which are introduced during the test for generalization. One of the predictions derived from this hypothesis is that an asymmetry in gradients should result when the SS and GSs consist of points, along the dimension of visible wavelength, where the discriminability function is sloping. That is, a response conditioned to the SS should be elicited more frequently by those GSs for which discriminability is increasing (coarse discrimination) than by GS for which discriminability is decreasing (fine discriminacion). The asymmetry of the gradients reported by Kalish was not in complete agreement with this hypothesis. In particular, the gradienc around 530 mp was asymmetrical in a direction opposite to that predicted. One purpose of the presenr study was to replicate, in part, the Kalish study; particularly, generalization around 530 mp. Another purpose was to determine the effects of a tranquilizing drug (perphenazine) on the generalization gradients. Seventeen male college studencs participated in this study. All Ss had normal color vision. The apparatus and procedure for eliciring stimulus generalization were, in all essential details, the same as those used by Kalish. The apparatus provided for variations in visible wavelength from 440 to 620 mp in steps of 10 mp. The experimental procedure involved the strengthening of a voluntary response, through verbal instructions, to a SS or reference stimulus prior to the test for generalization. In this study four lighcs, differing in wavelength, were used as SSs, namely: 470, 500, 530, and 580 mCr.Vhe lasc two SSs were the same as those used by Kalish. The same S was tested for generalization on two separate occasions; once 4 hr. after the administration of 20 mg. of perphenazine and once 4 hr. after the administration of a placebo.