Neural responses towards a speaker's feeling of (un)knowing

During interpersonal communication, listeners must rapidly evaluate verbal and vocal cues to arrive at an integrated meaning about the utterance and about the speaker, including a representation of the speaker's 'feeling of knowing' (i.e., how confident they are in relation to the utterance). In this study, we investigated the time course and neural responses underlying a listener's ability to evaluate speaker confidence from combined verbal and vocal cues. We recorded real-time brain responses as listeners judged statements conveying three levels of confidence with the speaker's voice (confident, close-to-confident, unconfident), which were preceded by meaning-congruent lexical phrases (e.g. I am positive, Most likely, Perhaps). Event-related potentials to utterances with combined lexical and vocal cues about speaker confidence were compared to responses elicited by utterances without the verbal phrase in a previous study (Jiang and Pell, 2015). Utterances with combined cues about speaker confidence elicited reduced, N1, P2 and N400 responses when compared to corresponding utterances without the phrase. When compared to confident statements, close-to-confident and unconfident expressions elicited reduced N1 and P2 responses and a late positivity from 900 to 1250 ms; unconfident and close-to-confident expressions were differentiated later in the 1250-1600 ms time window. The effect of lexical phrases on confidence processing differed for male and female participants, with evidence that female listeners incorporated information from the verbal and vocal channels in a distinct manner. Individual differences in trait empathy and trait anxiety also moderated neural responses during confidence processing. Our findings showcase the cognitive processing mechanisms and individual factors governing how we infer a speaker's mental (knowledge) state from the speech signal.