The influence of speech production on speech perception is well established in adults. However, because adults have a long history of both perceiving and producing speech, the extent to which the perception-production linkage is due to experience is unknown. We addressed this issue by asking whether articulatory configurations can influence infants' speech perception performance. To eliminate influences from specific linguistic experience, we studied preverbal, 6-mo-old infants and tested the discrimination of a nonnative, and hence never-before-experienced, speech sound distinction. In three experimental studies, we used teething toys to control the position and movement of the tongue tip while the infants listened to the speech sounds. Using ultrasound imaging technology, we verified that the teething toys consistently and effectively constrained the movement and positioning of infants' tongues. With a looking-time procedure, we found that temporarily restraining infants' articulators impeded their discrimination of a nonnative consonant contrast but only when the relevant articulator was selectively restrained to prevent the movements associated with producing those sounds. Our results provide striking evidence that even before infants speak their first words and without specific listening experience, sensorimotor information from the articulators influences speech perception. These results transform theories of speech perception by suggesting that even at the initial stages of development, oral-motor movements influence speech sound discrimination. Moreover, an experimentally induced "impairment" in articulator movement can compromise speech perception performance, raising the question of whether long-term oral-motor impairments may impact perceptual development.language acquisition | perception-production | infancy T he acquisition of language, arguably our most defining human capacity, relies on the seamless exchange of information between production and perception. In their seminal work, Eimas et al. (1) found that from 1 mo of age, human infants are equipped with perceptual sensitivities that enable them to discriminate speech sounds according to the boundaries used in human languages (see refs. 2, 3 for reviews of subsequent work). Within the first year, infant speech perception sensitivities adapt to the ambient language: The process of perceptual narrowing results in a decline in discrimination of nonnative distinctions (4, 5) and an improvement in the discrimination of native speech sound contrasts (6, 7). A similar trajectory is seen for audiovisual speech perception: Very young infants can match heard and seen speech (8-10), but by 9-10 mo, they do so reliably only for native speech sounds (11). Development of speech production progresses similarly. Although the infant vocal tract is anatomically immature and lacks the neuromuscular control of the adult vocal tract (12), the ability to produce communicative sounds (cries) is evident at birth (13, 14) and already reflects characteristics of the lang...

The period between six and 12 months is a sensitive period for language learning during which infants undergo auditory perceptual attunement, and recent results indicate that this sensitive period may exist across sensory modalities. We tested infants at three stages of perceptual attunement (six, nine, and 11 months) to determine 1) whether they were sensitive to the congruence between heard and seen speech stimuli in an unfamiliar language, and 2) whether familiarization with congruent audiovisual speech could boost subsequent non-native auditory discrimination. Infants at six- and nine-, but not 11-months, detected audiovisual congruence of non-native syllables. Familiarization to incongruent, but not congruent, audiovisual speech changed auditory discrimination at test for six-month-olds but not nine- or 11-month-olds. These results advance the proposal that speech perception is audiovisual from early in ontogeny, and that the sensitive period for audiovisual speech perception may last somewhat longer than that for auditory perception alone.

The relationship between speech perception and production is central to understanding language processing, yet remains under debate, particularly in early development. Recent research suggests that in infants aged 6-months, when the native phonological system is still being established, sensorimotor information from the articulators influences speech perception (Bruderer et al. 2015): the placement of a teething toy restricting tongue-tip movements interfered with infants’ discrimination of a non-native contrast, /Da/-/da/, that involves tongue-tip movement. This effect was selective: a different teething toy that prevented lip closure but not tongue-tip movement did not disrupt discrimination. We conducted two sets of studies to replicate and extend these findings. Experiments 1 and 2 replicated Bruderer et al. (2015), but with synthesized auditory stimuli. Infants discriminated the non-native contrast (dental /da/ - retroflex /Da/) (Experiment 1), but showed no evidence of discrimination when the tongue-tip movement was prevented with a teething toy (Experiment 2). Experiments 3 and 4 extended this work to a native phonetic contrast (bilabial /ba/-dental /da/). Infants discriminated the distinction with no teething toy present (Experiment 3), but when they were given a teething toy that interfered only with lip closure, a movement involved in the production of /ba/, discrimination was disrupted (Experiment 4). Importantly, this was the same teething toy that did not interfere with discrimination of /da/-/Da/ in Bruderer et al. (2015). These findings reveal specificity in the relation between sensorimotor and perceptual processes in pre-babbling infants, and show generalizability to a second phonetic contrast.

At the end of the target article, Keven & Akins (K&A) put forward a challenge to the developmental psychology community to consider the development of complex psychological processes - in particular, intermodal infant perception - across different levels of analysis. We take up that challenge and consider the possibility that early emerging stereotypies might help explain the foundations of the link between speech perception and speech production.