Intact Artificial Grammar Learning in Amnesia: Dissociation of Classification Learning and Explicit Memory for Specific Instances

Abstract

The present study investigates whether the ability to classify on the basis of rules can be learned independently of memory for the specific instances used to leach the rules. Thirteen amnesic patients and 14 control subjects studied letter strings generated by an artificial grammar. Subjects were then shown new letter strings and were instructed to classify them as grammatical or nongrammatical. Amnesic patients performed as well as normal subjects. However, amnesic patients performed more poorly than control subjects on a recognition test of the exemplars that had been presented. Amnesic patients also performed more poorly than control subjects when the instructions were to base the classification on explicit comparison with the original exemplars. The results show that classification learning based on exemplars of an artificial grammar can develop normally despite impaired memory for the exemplars themselves. Whereas exemplar memory depends on interactions between neocortex and the limbic system, classification learning may depend on interaction between neocortex and the neostriatum.

Sequence? What Sequence?: the human medial temporal lobe and sequence learning

“…2 The findings have instead motivated a 'relational' account hypothesizing that the MTL is critically involved in associative processes that bind multiple perceptual, cognitive, and motor aspects of events into a flexible memory trace. 3 In contrast to earlier null findings, [4][5][6][7][8] and favoring a relational view, some recent human neuroimaging and neuropsychological studies suggest that the MTL is necessary also for implicit learning of complex multievent associations. [9][10][11][12][13] Our neuroimaging study has provided critical evidence, in particular, that the higher-order associative and temporal structure of the representation being acquired is the primary factor determining recruitment of the human MTL.…”

Implicit learning: Below the subjective threshold

“…Knowlton, Ramus, and Squire (1992) found that, on the artificial grammar learning task, amnesics classified new exemplars at the same level as did control subjects (63% and 67%, respectively), but, on a recognition test ofthe exemplars that had been presented, they performed more poorly than did control subjects (62% and 72%, respectively), where chance is 50% in both cases. Presumably, normal controls were using some explicit memory of the exemplars to perform the recognition task but not the classification task.…”

Alternative strategies of categorization

“…Neuropsychological studies have already shown a dissociation between those two kinds of categorization (e.g. Knowlton et al, 1992;Squire and Knowlton, 1995). This explicit-implicit distinction may be relevant in some contrasts of rule-and similaritybased categorization procedures, as a rule is generally assumed to be explicitly represented whereas a retrieved exemplar need not be.…”