Heightened interference on implicit, but not explicit, tests of negative transfer: evidence from patients with unilateral temporal lobe lesions and normal old people

The present research investigated alternative explanations of heightened interference in AB-AC learning in individuals with memory loss related to medial temporal lobe dysfunction. In Experiment 1, patients with left or right temporal lobectomy and control subjects were administered the standard AB-AC test. Relative to the other groups, left temporal patients exhibited significant negative transfer that was characterized by large numbers of response intrusion errors. In Experiment 2, groups of community-dwelling old and young adults were administered the standard test and an implicit version in which, during AC testing, subjects were instructed to provide the first word that comes to mind in response to stimulus words. There were no differences between groups on either version. Of particular interest was that both groups made significantly more intrusion errors on the implicit test and did not differ on this measure. It was concluded that exaggerated interference in AB-AC learning, as reflected by response intrusion errors, is related to the use of implicit memory processes rather than a failure of inhibitory mechanisms. Memory-impaired individuals, who have a selective loss of explicit memory, are vulnerable on this task because they rely excessively on implicit memory processes.