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Earliest brain signatures of lexical access to spoken words: MEG evidence
Eighteenth Annual Meeting of the Cognitive Neuroscience Society, I9, 220
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How quickly can the listener’s brain access information about perceived words in the mental lexicon? Previous research has demonstrated a neurophysiological distinction between passively presented spoken words and pseudo-words as soon as 100-150ms after they could be identified, which has been used as evidence for automatic lexical access within the same time frame. However, one criticism of these studies is that they used the oddball paradigm and the mismatch negativity brain response, which require unnatural repetition of a small number of stimuli. Here we address this issue by directly comparing listeners’ neuromagnetic brain responses to multiple (N>100) distinct words (monosyllabic CVC) with phonologically and psycholinguistically matched pseudo-words. Each stimulus was auditorily presented only once in a random sequence, whilst volunteers were engaged in a distracter task (watching a film) used to minimise the influence of attention on brain responses. MEG was recorded using a high-density whole-head sensor array (Elekta-Neuromag). Event-related fields and their gradients were calculated relative to the onset of the word uniqueness point, determined in a behavioural gating study, which coincided with the onset of stimulus-final consonants. Significantly greater activity for words compared to pseudo-words – a putative index of lexical access – was observed as early as 60ms, with later effects also occurring at ~110-180 ms and ~300-400 ms. Minimum Norm Estimation revealed that left perisylvian sources underpinned the early lexical enhancement of the brain response. The results offer support for automatic rapid activation of neural memory circuits for spoken words within less than 1/5 second.