Academic journal article The Psychological Record

Differential Outcomes Effect: Increased Accuracy in Adults Learning Kanji with Stimulus Specific Rewards

Academic journal article The Psychological Record

Differential Outcomes Effect: Increased Accuracy in Adults Learning Kanji with Stimulus Specific Rewards

Article excerpt

In a standard discrimination procedure, common rewards are provided for correct responses to different stimuli. In a differential outcomes procedure, the rewards provided for correct responses vary according to the stimulus presented. The improvement in accuracy obtained with the latter procedure, compared to that obtained with common or random rewards, is known as the differential outcomes effect (DOE).

Trapold (1970) was the first to demonstrate a DOE. His experiment was designed to assess a two-process theory of learning. He suggested that an association is formed not only between the stimulus (S) and response (R), but also between the stimulus and the reinforcer ([S.sup.R]). The predicted S-[S.sup.R] association meant that the stimulus would come to elicit a learned representation/expectation of the reinforcer that consistently followed it. If this were the case, one would expect higher accuracy when differential outcomes are used, as additional discriminable information is available at the time of responding. Trapold tested this reasoning by teaching rats to discriminate between a clicker and a tone. Responses to the left bar were reinforced after presentation of the clicker. Responses to the right bar were reinforced after presentation of the tone. Rats who experienced differential outcomes received food for one type of correct response and sucrose solution for the other. Rats who experienced nondiffere ntial outcomes received either food or sucrose for both types of correct responses. Rats in the differential outcomes group learned the discrimination more quickly than rats in the latter control group. Support for the two-process theory of learning was obtained and the DOE was discovered.

Since the Trapold (1970) study, many articles have reported a DOE (see Goeters, Blakely, & Poling, 1992, for a review). This well-established effect has been found across a range of different species and with outcomes that differ in type and/or in quantity. However, the literature generalizing this effect to humans, particularly normally functioning humans, is sparse. As Overmier, Savage, and Sweeney (1999) point out, we need "to establish that the principles at hand are, in fact, general ones that apply to humans as well as animals" (p. 238).

A recent study by Maki, Overmier, Delos, & Gutmann (1995) looked at the effects of differential outcomes in humans. Children aged between 4 and 7 years were rewarded for discriminating two simple figures or shades. Differential outcomes consisted of food for one type of correct response and verbal praise for the other. Nondifferential outcomes consisted of food or praise allocated randomly after correct responses. Children who experienced the differential outcomes were significantly more accurate than those who did not. Differential tokens (backed up by nondifferential rewards) were also effective in facilitating performance. Additional testing demonstrated that those in the differential outcomes group formed expectancies for the rewards associated with each stimulus and were able to use these expectancies to solve a new discrimination problem.

The present study extended on previous research in a number of ways. First, it used a sample of normally functioning adults (university students). Second, it used a complex discrimination task; participants had to discriminate between 15 different kanji characters. All previously reported research has examined very simple learning situations where only two stimuli are discriminated. Finally, the current research manipulated the differential nature of both immediate and delayed outcomes.

It was expected that participants who experienced differential outcomes for correct responding would learn the kanji characters more quickly than those who did not.

Method

Participants

Sixty-three students (48 female and 15 male), aged between 18 and 38 years, were recruited from the University of Canberra. …

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