Dissociations in Processing Past Tense Morphology: Neuropathology and Behavioral Studies
Journal of Cognitive Neuroscience
Category-Specific Semantic Deficits in Focal and Widespread Brain Damage: A Computational Account
Journal of Cognitive Neuroscience
"Presemantic" Cognition in Semantic Dementia: Six Deficits in Search of an Explanation
Journal of Cognitive Neuroscience
Graded effects of regularity in language revealed by n400 indices of morphological priming
Journal of Cognitive Neuroscience
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The regular and irregular past tense has become a focus for recent debates about the structure of the language processing system, asking whether language functions are subserved by different neural and functional mechanisms or whether all processes can be accommodated within a single unified system. A critical claim of leading single mechanism accounts is that the relationship between an irregular stem and its past tense form is primarily semantic and not morphological in nature. This predicts an obligatory relationship between semantic performance and access to the irregular past tense, such that a semantic deficit necessarily leads to impairments on the irregulars. We tested this claim in a series of studies probing the comprehension and production of regular and irregular past tense forms in four semantic dementia patients, all of whom had profound semantic deficits. In two elicitation tasks and one auditory priming study, we found that three out of the four patients did not have a deficit for the irregular past tense, in spite of their semantic deficits. This argues against the view that the relationship between irregular past tense forms and their stems is primarily semantic, and more generally against the single system claim that morphological structure can be captured solely based on phonological and semantic relationships.