Latency shifts in the N2b component track phonological deviations in spoken words
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OBJECTIVE: We investigated event-related brain potentials (ERPs) elicited by a novel speech comprehension paradigm modelled after the neuropsychological Token Test. The objective of the study was to determine whether the ERPs were sensitive to differences in the initial phonemes of the speech stimuli. METHODS: Twenty-seven healthy subjects identified incorrect spoken sentences on the computerised Token Test (CTT). The incorrect spoken sentences contained one word that did not match the previously studied animations. The initial phonemes of these words were either different than or similar to the initial phonemes of their correct counterparts. RESULTS: Different initial phonemes were associated with an early N2b, while words having similar initial phonemes resulted in a substantially delayed N2b. CONCLUSION: The delayed latency effect was due to whether the incorrect word's initial phoneme matched or mismatched that of the expected word. In both cases, this component reflected a mismatch with an existing cognitive template maintained in phonological working memory. The results indicate that this mismatching effect reflected primarily attentional detection rather than language processing.
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