Emerging neurophysiologic evidence indicates that motor systems are activated during the perception of speech, but whether this activity reflects basic processes underlying speech perception remains a matter of considerable debate. Our contribution to this debate is to report direct behavioral evidence that specific articulatory commands are activated automatically and involuntarily during speech perception. We used electropalatography to measure whether motor information activated from spoken distractors would yield specific distortions on the articulation of printed target syllables. Participants produced target syllables beginning with /k/ or /s/ while listening to the same syllables or to incongruent rhyming syllables beginning with /t/. Tongue-palate contact for target productions was measured during the articulatory closure of /k/ and during the frication of /s/. Results revealed "traces" of the incongruent distractors on target productions, with the incongruent /t/-initial distractors inducing greater alveolar contact in the articulation of /k/ and /s/ than the congruent distractors. Two further experiments established that (i) the nature of this interference effect is dependent specifically on the articulatory properties of the spoken distractors; and (ii) this interference effect is unique to spoken distractors and does not arise when distractors are presented in printed form. Results are discussed in terms of a broader emerging framework concerning the relationship between perception and action, whereby the perception of action entails activation of the motor system. motor theory | perception-action relationship | speech production | interference | electropalatography O ne of the most exciting questions in the neuroscience of language concerns the involvement of the motor system in the perception of speech: is the motor system activated during speech perception, and does it play a causal role? Key studies using functional MRI have demonstrated that the brain regions involved in the perception of speech overlap with those involved in the production of speech (1) in a manner that seems to be articulator specific (2). Similarly, studies using transcranial magnetic stimulation (TMS) have shown potentiation of motor cortex representations of the lip (3) and tongue (4) muscles when participants listen to speech. Finally, recent work using repetitive TMS has revealed that disruption to regions of the premotor cortex impacts on perceptual discrimination of speech sounds (5) in a somatotopic manner (6). These studies are all consistent with the proposal that the motor system is activated (and perhaps even essential) in the perception of speech.However, although there is agreement that motor regions can be activated in speech perception studies, recent reviews of the literature have raised two important challenges over precisely what drives this activation (7,8). The first challenge stems from the fact that neuroimaging data have been inconsistent, with relatively few studies showing motor activity at a whole-br...

The manual gestures that accompany speaking have been analysed in terms of their form, their meaning, their role in the communicative act, and their timing with respect to the speech they accompany. Several schemes for categorizing these cospeech movements have been proposed, e.g. McNeill's (1992) iconic, metaphoric, deictic and beat gestures, and Kendon's (1994) distinction between substantive and pragmatic gestures. Among McNeill's gesture categories, beats are described as non-referential: simple flicks of the hand or finger, often performed repetitively and in rhythm, and lacking the complex phasing structure of other gesture types. For referential gestures, this complex phasing can include (in addition to the core stroke phase) preparation, pre-or post-stroke hold and recovery (Kendon 1980). Studies of adult speech show that many gestures are timed to overlap with phrase-level prosodic accents (Loehr 2004, Yasinnik et al. 2004); in at least one corpus of academic-lecture speech (Shattuck-Hufnagel et al. in prep.) these gestures are largely non-referential, like beats. We present evidence that this type of non-referential gesture can also have complex phasal structure in adults, and that children as young as 6 have such gestures in their repertoire, although less skillfully produced. Potential relations between prosody and gesture are discussed.

Speech units are reported to be hyperarticulated in both infant-directed speech (IDS) and Lombard speech. Since these two registers have typically been studied separately, it is unclear if the same speech units are hyperarticulated in the same manner between these registers. The aim of the present study is to compare the effect of register on vowel and tone modification in the tonal language Mandarin Chinese. Vowel and tone productions were produced by 15 Mandarin-speaking mothers during interactions with their 12-month-old infants during a play session (IDS), in conversation with a Mandarin-speaking adult in a 70 dBA eight-talker babble noise environment (Lombard speech), and in a quiet environment (adult-directed speech). Vowel space expansion was observed in IDS and Lombard speech, however, the patterns of vowel-shift were different between the two registers. IDS displayed tone space expansion only in the utterance-final position, whereas there was no tone space expansion in Lombard speech. The overall pitch increased for all tones in both registers. The tone-bearing vowel duration also increased in both registers, but only in utterance-final position. The difference in speech modifications between these two registers is discussed in light of speakers' different communicative needs.