This study explored the status of an English grammatical distinction in the language of individuals who have never been able to encode that distinction previously. English past tense marking was used as a context to examine regular and irregular verb class distinctions in the language of two adults with severe congenital physical impairments who rely on augmentative and alternative communication (AAC) systems to communicate. In the subjects' lexically based AAC systems, past tense was marked on regular verbs and irregular verbs using the same strategy. The subjects accessed their AAC displays using four-digit eye gaze number codes. They were shown a novel affixation strategy through manipulation of the four-digit codes that allowed them to mark past tense on regular verbs via an affixation process. Their semantic strategy for marking past tense on irregular verbs was not changed. The subjects' patterns of use of the two strategies on exemplars of each verb class revealed limited evidence of distinctive use of the two strategies based on verb class membership. Theoretical and clinical implications are discussed.
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