Sutherland, Mackintosh, and Wolfe (1965) demonstrated that continuous reinforcement given subsequent to partial reinforcement resulted in superior resistance to extinction than did continuous reinforcement administered prior to partial reinforcement. Because the experimenters did not make compensations for different acquisition asymptotes in their analysis of the extinction data, the interpretation of their results is questionable. Thelos and McGinnis (1967) obtained results contrary to those obtained by the latter experimenters. This study was run in order to obtain additional information pertaining to the effects of shifts of reinforcement schedules on resistance to extinction. Extended acquisition trials were used with the expectation of bringing the six experimental groups up to the same terminal asymptotic levels. When Ss were approximately 45 days old, Ss were randomly assigned to one of six acquisition conditions. These conditions were: 96 partial reinforcement trials, 192 partial reinforcement trials, 96 partial reinforcement trials followed by 96 continuous reinforcement trials, 96 continuous reinforcement trials followed by 96 partial reinforcement trials, 192 continuous reinforcement trials, and 96 continuous reinforcement trials. Following training in a straight runway, all Ss received 60 nonreward trials given in blocks of 6 trials a day. Time measures were taken of runway performance on acquisition and extinction trials. The results supported the hypothesis that extended training would produce equivalent terminal asymptotic running speeds in acquisition. None of the hypotheses made by Sutherland, Mackintosh, and Wolfe (1965) or by Thelos and McGinnis (1967) were supported by the results of the experiment; no significant partial reinforcement effect was obtained. / Arts, Faculty of / Psychology, Department of / Graduate

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A model based on the laws of classical conditioning is posed as an explanation for the McCollough Effect, an orientation-specific color aftereffect. This model stands as an alternative to the color-coded edge detector hypothesis. Background and relevant issues are presented. Two experiments were performed. The first demonstrated that an auditory stimulus causes the effect to appear stronger to some subjects, a disinhibiting effect. It was also shown that some subjects experience spontaneous recovery of the effect after it has been extinguished.

Traditionally, the procedure of feeding an organism in a fear-producting situation has been viewed as having a fear-reducing effect, called counterconditioning. English and English define counterconditioning as the procedure of conditioning a second and conflicting response to a conditioned stimulus that is not simultaneously being reinforced. Fear is reduced by conditioning to the fear-producing stimuli the incompatible emotional responses associated with eating (e.g.--Miller, 1951) The strength of fear was illustrated by Miller in 1951. He found that albino rats, trained to run down an alley to secure food at a distinctive place and motivated by a 46-hour hunger, would pull with a force of 50 gm. if they were restrained near the food. Studeis done by Faber (1948), Jones (1924) and Wolpe (1952) found that Ss fed in a fear-producing situation were consequently less fearful than Ss not receving food in the situation. In Nelson's second experiement the results suggested that these experiemtns primarily reflected the effects of exposure. The present experimentis designed to examine the difference in results between the Incentive and the Incentive Control groups, if the conditions are changed. The Ss in the Incentive Control group are forced to spend an amount of time in the two compartments equal to the time spent in each compartment by a matched S in the Incentive conditin, but with food present. The present experiment tried to indicate that at least for the Incentive and the Incentive Control groups the variable of free, as opposed to forced, exposure is a significant factor

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