Hearing sounds as words: Neural responses to environmental sounds in the context of fluent speech

Environmental sounds (ES) can be understood easily when substituted for words in sentences, suggesting that linguistic context benefits may be mediated by processes more general than some language-specific theories assert. However, the underlying neural processing is not understood. EEG was recorded for spoken sentences ending in either a spoken word or a corresponding ES. Endings were either congruent or incongruent with the sentence frame, and thus were expected to produce N400 activity. However, if ES and word meanings are combined with language context by different mechanisms, different N400 responses would be expected. Incongruent endings (both words and ES) elicited frontocentral negativities corresponding to the N400 typically observed to incongruent spoken words. Moreover, sentential constraint had similar effects on N400 topographies to ES and words. Comparison of speech and ES responses suggests that understanding meaning in speech context may be mediated by similar neural mechanisms for these two types of stimuli.