The sound of confidence and doubt

Feeling of knowing (or expressed confidence) reflects a speaker's certainty or commitment to a statement and can be associated with one's trustworthiness or persuasiveness in social interaction. We investigated the perceptual-acoustic correlates of expressed confidence and doubt in spoken language, with a focus on both linguistic and vocal speech cues. In Experiment 1, utterances subserving different communicative functions (e.g., stating facts, making judgments) produced in a confident, close-to-confident, unconfident, and neutral-intending voice by six speakers, were then rated for perceived confidence by 72 native listeners. As expected, speaker confidence ratings increased with the intended level of expressed confidence; neutral-intending statements were frequently judged as relatively high in confidence. The communicative function of the statement, and the presence vs. absence of an utterance-initial probability phrase (e.g., Maybe, I'm sure), further modulated speaker confidence ratings. In Experiment 2, acoustic analysis of perceptually valid tokens rated in Experiment 1 revealed distinct patterns of pitch, intensity and temporal features according to perceived confidence levels; confident expressions were highest in fundamental frequency (f0) range, mean amplitude, and amplitude range, whereas unconfident expressions were highest in mean f0, slowest in speaking rate, with more frequent pauses. Dynamic analyses of f0 and intensity changes across the utterance uncovered distinctive patterns in expression as a function of confidence level at different positions of the utterance. Our findings provide new information on how metacognitive states such as confidence and doubt are communicated by vocal and linguistic cues which permit listeners to arrive at graded impressions of a speaker's feeling of (un)knowing.