Effects of overtraining on reversal and nonreversal learning on concurrent discriminations in rats

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 overtrainin