When can listeners detect disfluency in spontaneous speech?

Three experiments investigated listeners' ability to detect disfluency in spontaneous speech. All employed gated word recognition with judgments of disfluency for spontaneous utterances containing disfluencies and for three kinds of fluent control utterances from the same six speakers: repetitions of corrected recordings of original disfluent items, spontaneous fluent utterances loosely matched in structure to the disfluent items, and repetitions of those spontaneous fluent items. In Experiment 1, 120 stimuli were word-level gated and presented to 20 subjects for word identification and for judgments on whether the utterance was about to become disfluent. Listeners were unable to predict disfluency reliably. New subjects (N = 20, 43) judged whether the same utterances had already become disfluent at each word gate in Experiment 2 or at each 35 ms gate in Experiment 3. Subjects reliably detected existing disfluencies during the first word gate after the interruption and before they recognized the word. Though more common around disfluencies than at similar points in controls, failures of word identification were not reliably associated with detection. Results are discussed in the light of computational models of disfluency detection.

Limited visual control of the intelligibility of speech in face-to-face dialogue.

Speakers are thought to articulate individual words in running speech less carefully whenever additional nonacoustic information can help listeners recognize what is said (Fowler & Housum, 1987; Lieberman, 1963). Comparing single words excerpted from spontaneous dialogues and control tokens of the same words read by the same speakers in lists, Experiment 1 yielded a significant but general effect of visual context: Tokens introducing 71 new entities in dialogues in which participants could see one another's faces were more degraded (less intelligible to 54 naive listeners) than were tokens of the same words from dialogues with sight lines blocked. Loss of clarity was not keyed to moment-to-moment visual behavior. Subjects with clear sight lines looked at each other too rarely to account for the observed effect. Experiment 2 revealed that tokens of 60 words uttered while subjects were looking at each other were significantly less degraded (in length and in intelligibility to 72 subjects) vis-à-vis controls than were spontaneous tokens of the same words produced when subjects were looking elsewhere. Intelligibility loss was mitigated only when listeners looked at speakers. Two separate visual effects are discussed, one of the global availability and the other of the local use of the interlocutor's face.

The unintelligibility of speech to children: effects of referent availability.

Speech addressed to children is supposed to be helpfully redundant, but redundant or predictable words addressed to adults tend to lose intelligibility. Word tokens extracted from the spontaneous speech of the parents of 12 children aged 1; 10 to 3; 0 and presented in isolation to adult listeners showed loss of intelligibility when the words were redundant because they had occurred in repetitions of an utterance (Experiment 1) or referred to an entity which was physically present when named (Experiment 2). Though children (N = 64; mean age 3; 5, S.D. 6.1 months) recognized fewer excerpted object names than adults (N = 40), less intelligible tokens appeared to induce child listeners to rely on the word's extra-linguistic context during the recognition process (Experiment 3), much as such tokens normally induce adults to rely on discourse context. It is proposed that interpreting parental utterances with reference to non-verbal context furthers linguistic development.