Impact of associative word learning on phonotactic processing in 6-month-old infants: A combined EEG and fNIRS study

During early language development native phonotactics are acquired in a ‘bottom-up’ fashion, relying on exquisite auditory differentiation skills operational from birth. Since basic lexico-semantic abilities have been demonstrated from 6 months onwards, ‘top-down’ influences on phonotactic learning may complement the extraction of transitional probabilities in phonotactic learning. Such a bidirectional acquisition strategy predicts, that familiarization with (proto)words should affect processing of untrained word-forms of similar phonological structure. We investigated 6-month-old infants undergoing an associative training to establish a pseudoword-pseudoobject link. Comparison between pre- and post-training responses to trained and untrained items allowed investigating training effects. Additionally phonotactic status (50% legal, 50% illegal with regard to German) allowed investigating influences of previous language experience. EEG and functional near-infrared spectroscopy (fNIRS) provided measures of electrophysiological and hemodynamic responses. We find evidence for a robust effect of associative training on pseudoword processing when presented in isolation. This transferred to untrained items. Previous linguistic experience showed a much weaker effect. Taken together the results suggest that sensitivity to phonotactic contrasts is present at 6 months, but that acceptance as lexical candidates is rapidly modulated when word forms following non-native phonotactics become potentially meaningful due to repeated exposure in a semantic context.