Academic journal article The Psychological Record

Acquired Equivalence of Discriminative Stimuli Following Two Concurrent Discrimination Learning Tasks as a Function of Overtraining in Rats

Academic journal article The Psychological Record

Acquired Equivalence of Discriminative Stimuli Following Two Concurrent Discrimination Learning Tasks as a Function of Overtraining in Rats

Article excerpt

There are many studies on stimulus classes formation in pigeons and in rats. They make it clear that both pigeons and rats have an ability to form stimulus classes or stimulus-stimulus associations between stimuli. Especially, some studies have reported, using a whole-partial reversal procedure, that both rats and pigeons form stimulus classes between discriminative stimuli that signal either reward or nonreward during overtraining in two concurrent discriminations (Delius et al., 1995; Nakagawa, 1978, 1986, 1992, 1998; Zentall et al., 1991). A specific question, however, remains. Are stimulus classes between the discriminative stimuli which both rats and pigeons established during overtraining valid? This is a very important and even fundamental issue in behavior analysis and one that has received far too little experimental attention.

Edwards, Jagielo, Zentall, and Hogan (1982) have reported that pigeons are capable of acquiring an arbitrary stimulus class. In this experiment, pigeons were given two stimulus matching-to-sample tasks: shape matching-to-sample task on some trials and hue matching-to-sample task on other trials in a random order within session, in which correct matches of one hue and one shape were followed by corn and correct matches of the other hue and the other shape were followed by wheat. On a transfer test, when the hue samples were presented with shape comparisons, and vice versa, pigeons chose the comparisons associated with the same outcome as the sample. This finding indicates that a stimulus class consists of arbitrary stimuli, related to each other through their association with a same outcome in pigeons.

Urcuioli, Zentall, Jackson-Smith, and Steirn (Experiment 2 in 1989), using a design analogous to that used by Spradlin, Cotter, and Bexley (1973), trained pigeons on a conditional discrimination involving hue and line samples in Phase 1 training (red-vertical line and green-horizontal line associations for example). In Phase 2 training, pigeons were trained on a second task involving the hue samples from Phase 1 training and a new pair of comparison stimuli (red-vertical line and green-horizontal line associations for example). In Phase 3 test, pigeons matched the line samples from Phase 1 training to the comparisons from Phase 2 training. Urcuioli et al. (1989) found that when Phase 3 associations were consistent with the hypothesized stimulus classes, pigeons performed well above chance, whereas when the associations were inconsistent with the stimulus classes, performance levels were below chance. This finding indicates that pigeons form stimulus classes on a basis of reinforcement concordance.

Vaughan (1988) demonstrated that pigeons could form stimulus classes using a different procedure. In Vaughan's experiment, pigeons were trained to respond to a set of 20 randomly selected slides (S+s) and to not respond to a second set of 20 stimuli (S-s). After pigeons completed acquisition, the contingencies associated with both sets were reversed, and then reversed again repeatedly. After a large number of reversals, pigeons responded correctly to stimuli presented later in a session following presentation of the first few stimuli in each set. Apparently, pigeons had formed a stimulus class for each of the two stimulus sets.

Zentall et al. (1991) showed that after many-to-one overtraining in which a red (R) and vertical-line (V) sample were associated with a circle (C) comparison and a green (G) and horizontal-line (H) sample were associated with a dot (D) comparison, pigeons acquired their reversal learning faster when both sets of associations were reversed than when only one set was reversed. This finding makes it clear that pigeons form stimulus classes.

Nakagawa (1978, 1986, 1992, 1998), using a whole-partial reversal procedure which compared rats' performance on whole reversal sessions (both stimulus pairs reversed, from A+C-, B+D- to A-C+, B-D+ for example) with rats' performance on partial reversal sessions (only one pair reversed, from A-C+, B-D+ to A+C-, B-D+ for example), reported that rats could form stimulus classes. …

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