No abstract

A study of 1000-Hz intensity discrimination is reported in which single tones were identified as the louder or softer of two alternatives differing slightly in energy. Tones were phase locked and fixed in duration (150 msec). Feedback was given following each judgment. Psychometric functions are presented and a masking curve is computed. The masking curve is found to be linear above 25-dB sensation level, and the slope is computed as 15/16. These results are interpreted as reflecting a form of energy discrimination similar to that proposed in noise masking.

In two experiments rats were given either continuously reinforced or partially reinforced pretraining prior to discrimination training. Pretraining was given to both stimuli to be discriminated, to one of the stimuli, to different stimuli, or to no stimuli and was compared to a control condition with no pretraining. There was little effect of pretraining on choice measures of learning and varied effects on latency measures. Latencies were most affected by partially reinforced pretraining. Although the choice data supported the predictions of Sutherland and Mackintosh's attentional theory and the latency data offered partial support for the opposing predictions of Amsel and Ward's frustration theory, it was pointed out that neither theory could handle the data that the other relies upon. Discrepancies found between choice and latency measures suggest that they measure two different processes in discrimination learning.

Two experiments with rats investigated learning about S+ and S-during various stages of discrimination training. Transfer tests, in which either S+ or S-was retained, or two new stimuli were presented, were used to assess learning early in acquisition, at criterion, or following overtraining. Both choice and latency measures were used. Results indicated that learning about S+ occurs early in acquisition when noncorrection training is given, and little improvement occurs after that time, at least up to 70 trials of overtraining under present conditions. Learning about S-begins somewhat later in acquisition and continues throughout overtraining. When correction training is used, learning about Soccurs earlier in acquisition, and further learning about both S+ and S-occurs during overtraining.Most theories of simultaneous discrimination learning ha ve ,been more concerned with the rate of discrimination between two stimuli than with possible differences in rate of learning about the two stimuli considered separately. In simultaneous discrimination experiments, the two stimuli to be differentiated are present on every trial. Relative choice of the two stimuli is measured, and the organism is said to have learned the discrimination when it consistently chooses the positive stimulus (S+) over the negative stimulus (S-). Some theories, such as Spence's (1936), make provision for differential growth of approach and avoidance tendencies, but the parameters have rarely been pursued in simultaneous discrimination designs. Sutherland and Mackintosh's theory (1971) places primary emphasis on the growth of attention to the dimensions comprising the stimuli and leaves unspecified rate of development of approach to positive values of those dimensions vs. avoidance of negative values. Some of the relevant literature is reviewed below.Response to S+ and S-in Early Acquisition (presolution Stage) Some early studies with rats provide a small amount of conflicting data (Krechevsky, 1938;McCullogh & Pratt, 1934). In some of these studies it was shown that at least some early learning about reinforcement contingencies took place because acquisition was retarded when the contingencies were reversed. In other studies, no retardation was found. In either event, the reversal method used does not allow a determination of separate response tendencies to S+ and S-, since the reinforcement values of both stimuli were changed at the same time. One set of studies reversed only one stimulus and combined it with a new stimulus (Lashley & Wade, 1946). Greater retardation in learning a discrimination was found when S-was made positive than when S+ was made negative. This result suggests earlier learning about S-than S+, since changing S-was more disruptive. However, the technique of changing a stimulus from positive to negative or vice versa may be unnecessarily complex. A simple technique would be to substitute a new stimulus either for S+ or S-, rather than reversing reinforcement values. Response to S+ and S-at CriterionSeveral studies have show...