A Factor Affecting Stimulus Classes Formation in Concurrent Discriminations in Rats

Abstract

Two experiments examined whether or not rats formed stimulus classes on a basis of same response (i.e., shared common response) during overtraining. In Experiment 1, rats were trained on two discriminations in a straight runway, then trained on conditional successive discriminations in a Y maze. Group C, in which rats were required to choose the same goal box when the original positive stimulus or the negative one was presented on the entrance of each goal box, learned shift problems faster than Group IC, in which rats were required to choose the right goal box when one of positive stimuli was presented and to choose the left goal box when the other was presented as well as negative stimuli, after overtraining, but not after criterion training . In Experiment 2, rats were trained on two discriminations in the Y maze, and then they were trained on either whole reversal (Group W) in which two tasks were reversed or partial reversal (Group P) in which one of two tasks was reversed in a straight runway. Group W learned their reversal faster than Group P after overtraining , but not after criterion training. These results indicate that the same response is a factor affecting stimulus classes formation in rats.There are two main views on the formation mechanism of stimulus classes: The one is categorization processes based on simple similarity between stimuli (Bhatt & Wasserman, 1989;Fersen & Lea, 1990; Vaughan & Herrstein, 1987), the other is stimulus associations on the basis of reinforcement concordance (Deli us, Ameling, Lea, & Staddon, 1995;Edwards, Jagielo, Zentall, & Hogan, 1982;Nakagawa, 1986Nakagawa, , 1992Nakagawa, , 1998 Urcuioli, Zentall, Jackson, Smith, & Steirn, 1989, 1998. However, it is important to note that such stimulus associations mechanism as postulated in Nakagawa (1986, 1992, 1998) and Delius et al. (1995) is not necessarily in conflict with categorization processes based on simple similarity between stimuli. Conversely, it seems likely that in nature both principles may often act in consonance. A specific question, however, remains. What precise conditions favor the formation of stimulusRequests for reprints should be sent to E. Nakagawa,

Shift Learning in Matching-to-Sample Discriminations in Rats as a Function of Overtraining

“…That is, after criterion training or some overtraining , the animals may form stimulus-stimulus associations based on reinforcement concordance, whereas after enough overtraining animals form stimulus-stimulus associations on the basis of the same response following the same consequence. This was supported by the more recent findings of Nakagawa (1998Nakagawa ( , 1999aNakagawa ( , 1999bNakagawa ( , 1999dNakagawa ( , 2000aNakagawa ( , 2000c.…”

“…The second is stimulus association based on the same response following the same consequence (Delius et aI., 1995;Nakagawa,1986Nakagawa, , 1992aNakagawa, , 1992bNakagawa, , 1993aNakagawa, , 1993bNakagawa, , 1998Nakagawa, , 1999aNakagawa, , 1999bNakagawa, , 1999cNakagawa, , 1999dNakagawa, , 2000aNakagawa, , 2000bNakagawa, , 2000cNakagawa, , 2001a. In Experiments 1 and 2 of the present study, a very restricted set of repeated test stimuli was used in Phase 1 matching-(or nonmatching-) to-sample discrimination training.…”

“…That is, the nonshifted pigeons learned their shift task more rapidly than did the shifted pigeons. The second method is a whole-partial reversal paradigm (Oelius, Ameling, Lea, & Staddon, 1995;Oube, Callahan, & Mcllvane, 1993;Nakagawa, 1978Nakagawa, , 1986Nakagawa, , 1992bNakagawa, , 1998Nakagawa, , 1999aNakagawa, , 1999bNakagawa, , 1999cNakagawa, , 1999dNakagawa, , 2000aVaughan, 1988;Zentall, Sherburne, Steirn, Randall, Roper & Urcuioli, 1992;Zentall , Steirn, Sherburne, & Urcuioli, 1991). In this paradigm, for example, in a series of experiments of Nakagawa, rats were concurrently trained to discriminate four simple stimuli (A, B, C, 0 for example) where responses to the two stimuli were rewarded (A+ B+ for example) and responses to the other stimuli were not rewarded (C-0-for example) to reach a criterion or were overtrained.…”

Overtraining, Extinction, and Shift Learning in Matching-to-Sample Discriminations in Rats

“…They make it clear that both species treat stimuli as being equivalent if they signal the same outcome in either concurrent discriminations (Delius, Ameling, Lea, & Staddon , 1995; Dube, Callahan , & Mcllvane, 1993;Nakagawa, 1978Nakagawa, , 1986Nakagawa, , 1992aNakagawa, , 1998Nakagawa, , 1999aNakagawa, , 1999bNakagawa, , 1999cNakagawa, , 1999dNakagawa, , 2000b a) or matching-(or nonmatching)-to-sample discriminations (Aggleton , 1985;Mumby, Pine, & Wood, 1990;Nakagawa, 1992bNakagawa, , 1993aNakagawa, , 1993bNakagawa, , 1999bNakagawa, , 2000aNakagawa, , 2000c Nakagawa, b, 2001Rothblat & Hayes, 1987; Urcuioli, 1977; Urcuioli & Nevin , 1975;Zentall & Hogan, 1974, 1976 Zentall , Sherburne, Steirn, Randall , Roper, & Urcuioli , 1992; Zentall , Steirn, Sherburne, & Urcuioli , 1991). Nakagawa (200 1 c) has examined effects of overtraining on nonshift and shift (i.e., reversal shift) learning in a matching-(or nonmatching)-tosample discrimination.…”

“…And what accounts for the superiority of Group Nonshift to Group Reversal in discrimination performance? According to the theory of Nakagawa (1978Nakagawa ( , 1986Nakagawa ( , 1992aNakagawa ( , 1993bNakagawa ( , 1998Nakagawa ( , 1999aNakagawa ( , 1999cNakagawa ( , 1999d, during the original training animals learn a connection between a positive stimulus and an approach response as well as a connection between a negative stimulus and an avoidance response for each discrimination task in concurrent discriminations. But during overtraining they also form associations between the discriminative stimuli with the same response assignment.…”