Effects of Overtraining on Reversal and Nonreversal Learning on Concurrent Discriminations in Rats

Abstract

Two experiments examined the positive extradimensional shift effect of overtraining in concurrent mixed discriminations. In Experiment 1 rats were trained on two concurrent simultaneous discriminations and then either reversed on both tasks (Group W), or reversed on one task while a second novel discrimination was introduced (Group eMS). After initial training, two novel discrimination tasks were presented to a third group of rats (Group EDS). Overtraining facilitated extradimensional shift in Group eMS, whereas it neither facilitated nor retarded shift learning in Group EDS. In Experiment 2 using two concurrent go/no-go discriminations with the same design as in Experiment 1, overtraining facilitated extradimensional shift in Group eMS, whereas it delayed the corresponding shift in Group EDS. These findings make it clear that an important factor that determines the animals performance is not only stimulus properties but also the nature of the response required.The old dispute about whether or not overtraining facilitates reversal and non reversal (Le., extradimensional) shifts in a single discrimination task has generally been resolved by conceding that it facilitates reversal shift, whereas it delays or does not facilitate at least non reversal (Le., extradimensional) shift with a few exceptions, in which overtraining facilitates extradimensional shift (Hall, 1974;Mandler, 1968;Mandler & Hooper, 1967;Waller 1970Waller , 1971). However, recently some studies, using a . whole-partial reversal procedure, have reported that overtraining facilitated reversal shift (Le., a positive overtraining reversal effect: positive ORE) under one training condition, say, of a whole reversal condition, in which both discrimination tasks were reversed, whereas it retarded reversal shift (Le., a negative ORE) under the other training condition, say, of a partial reversal condition, in which only one of them was reversed, in concurrent discriminations (Nakagawa, 1978(Nakagawa, , 1986 Correspondence concerning this article should be sent to Esho Nakagawa,

A Factor Affecting Stimulus Classes Formation in Concurrent Discriminations in Rats

“…The remaining rats were required to choose the right goal box if either one of the original positive stimulus (A+) or one of the original negative stimulus (C-) was presented on the entrance door of each goal box, and they were required to choose the left goal box if either the other of the original positive stimulus (B+) or the other of the original negative stimulus (D-) was presented (inconsistent condition; Group IC). If rats formed stimulus classes on a basis of the same response during overtraining, as the cue-associations theory (Nakagawa, 1986(Nakagawa, , 1992 postulated , rats trained in the consistent condition should then learn transfer more rapidly than those trained in the inconsistent condition after overtraining, but not after criterion training…”

“…In each group, suppression generalized more readily from N to the stimulus that had received the same initial training as had been given to N. Nakagawa (1986Nakagawa ( , 1992, Zentall, Steirn, et al (1991), Zentall, Sherburne, et aI., (1992), Delius et al (1995), Dube et al (1993), and Hall et al (1993) suggest that rats and pigeons can form stimulus classes on a basis of reinforcement concordance. Nakagawa (1978Nakagawa ( , 1986Nakagawa ( , 1992 has asserted that, during the original discrimination training, rats 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. But during overtraining they also form associations between the discriminative stimuli on a basis of the same response following the same consequence in concurrent discriminations.…”

“…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.…”

“…Using a whole-partial reversal procedure which compared rats' performances on whole reversal sessions (both stimulus pairs reversed, from A+C-, B+O-to A-C+, B-O+ for example) with those on partial reversal sessions (only one pair reversed, from A-C+, B-O+ to A+C-, B-0+ for example), Nakagawa (1978Nakagawa ( , 1986Nakagawa ( , 1992Nakagawa ( , 1998 has shown that rats form stimulus classes between the discriminative stimuli on the basis of the same response during overtraining in concurrent discriminations. In Nakagawa's experiments, rats were trained to criterion or overtrained on two concurrent discriminations (A+C-, B+O-for example) in Phase 1 training in both a simultaneous (Nakagawa, 1986(Nakagawa, , 1998) and a go-no go successive concurrent discriminations (Nakagawa, 1992(Nakagawa, , 1998.…”

“…In Nakagawa's experiments, rats were trained to criterion or overtrained on two concurrent discriminations (A+C-, B+O-for example) in Phase 1 training in both a simultaneous (Nakagawa, 1986(Nakagawa, , 1998) and a go-no go successive concurrent discriminations (Nakagawa, 1992(Nakagawa, , 1998. After completing Phase 1 training, rats received either partial reversal (only one pair reversed from A+C-, B+O-to either A-C+, B+O-or A+C-, B-O+ for example) or whole reversal (both stimulus pairs reversed , from A+C-, B+O-to A-C+, B-O+ for example).…”