The Differential Outcomes Effect: A Useful Tool to Improve Discriminative Learning in Humans.

One of the most robust and reliable learning phenomena documented in the animal learning literature is the enhancement of discriminative performance by differential outcomes. To date, very few studies have focused on this effect in humans. The results obtained in these studies support the potential use of the differential outcomes procedure in human beings as a technique for facilitating memory and learning of conditional discriminations. The main aim of this paper is to describe the differential outcomes effect and to summarize experimental studies of this effect in human beings. Key words: differential outcomes effect, discriminative learning and humans ********** In daily life human beings learn to discriminate between different events and to act in consequence. For example, let us imagine that it is raining and we are going out. The rain is for us a discriminative signal that indicates what decision we should make: to carry an umbrella to avoid getting wet. If instead of taking the umbrella we take sun glasses we will end up wet and we may even catch a cold. This type of learning (it's raining-catch an umbrella), called discriminative learning, is really important in our daily life. However, there are people who have discriminative learning deficits so it is necessary to use techniques to ameliorate them. The present paper summarizes studies concerned with a technique that seems to be useful for teaching and training difficult discriminations. I refer to the differential outcomes effect. WHAT IS THE DIFFERENTIAL OUTCOMES EFFECT? The differential outcomes effect, refers specifically to the increase in speed of acquisition or terminal accuracy that occurs in a conditional discrimination training when each discriminative stimulus-response sequence is always followed by a particular outcome (for example, a different type of reinforcer). Trapold (1970) provided an early demonstration of this phenomenon. He exposed rats to a discrimination problem that required a response to one lever (for example, the right lever -R1-) in the presence of one stimulus (a tone), and a response to a second lever (the left lever -R2-) in the presence of another stimulus (a click). Trapold observed an increased rate of acquisition and greater accuracy when the correct R1 was followed by pellets and the correct R2 was followed by sucrose than when both correct responses produced the same reinforcer, for instance, pellet. Let us return for a moment to daily life. We are going to imagine a child that have to learn to cross a street in the presence of a green signal and to stop when the signal is red. The results obtained by Trapold suggest that the child might learn the task better when he receives differential outcomes following his correct responses (for instance, a kiss when he correctly chooses to cross the street and the phrase 'well done' when he correctly chooses to stop). The differential outcomes effect has been demonstrated with a considerable range of subjects and with a variety of different consequences (for a review, see Goeters, Blakely and Poling, 1992). The matching to sample task (MTS) has been used in most studies. This task usually consists of the presentation of a sample stimulus followed by the presentation of two choice alternatives or comparison stimuli. The participant has to choose the alternative that 'goes with' the sample. In the differential outcomes condition correct responses to one sample stimulus are followed by one reinforcer and correct responses to the other sample stimulus are followed by a different reinforcer. A common variation of the matching to sample task inserts a time delay between the offset of the sample stimulus and the onset of the comparison stimuli. This arrangement is referred to as delayed matching to sample task (DMTS). Figure 1 shows an example of the DMTS. An interesting result, reported in several studies, is that the magnitude of the differential outcomes effect increases when there is a long delay between the discriminative stimulus and the choice opportunity (e. …