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...

Mutual exclusivity is the assumption that each object has only one category label. Prior research suggests that bilingual infants, unlike monolingual infants, fail to adhere to this assumption to guide word learning. Yet previous work has not addressed whether bilingual infants systematically interpret a novel word for a familiar object (i.e. an object with a known category label) as a second category label. We addressed this question by exploring bilingual and monolingual infants' use of mutual exclusivity in a task in which they heard a novel label for a familiar object with a salient color (e.g. an aqua-colored dog). They were subsequently tested with two trials that probed whether they interpreted the word as a second category label for the object (e.g. another word meaning dog) or as a label for one of the object's salient properties, namely its color (e.g. a word meaning aqua). Bilingual infants failed to adhere to mutual exclusivity and interpreted the novel word systematically as a second object category label for the familiar object. In contrast, consistent with their use of mutual exclusivity, monolingual infants rejected the novel word as a second category label, and instead showed some evidence of interpreting it as a property (color) term for the familiar object. The findings suggest that both bilingual and monolingual infants are systematic in their interpretation of a novel label for a familiar object, but that they show different interpretations of that label. We thus argue that theoretical accounts of early word learning must consider the crucial role of linguistic experience.

The coarse coding hypothesis (Jung-Beeman 2005) postulates that the cerebral hemispheres differ in their breadth of semantic activation, with the left hemisphere (LH) activating a narrow, focused semantic field and the right (RH) weakly activating a broader semantic field. In support of coarse coding, studies (e.g., Faust and Lavidor 2003) investigating priming for multiple senses of a lexically ambiguous word have reported a RH benefit. However, studies of mediated priming (Livesay and Burgess 2003; Richards and Chiarello 1995) have failed to find a RH advantage for processing distantly-linked, unambiguous words. To address this debate, the present study made use of a multiple priming paradigm (Balota and Paul, 1996) in which two primes either converged onto the single meaning of an unambiguous, lexically-associated target (LION-STRIPES-TIGER) or diverged onto different meanings of an ambiguous target (KIDNEY-PIANO-ORGAN). In two experiments, participants either made lexical decisions to targets (Experiment 1) or made a semantic relatedness judgment between primes and targets (Experiment 2). In both tasks, for both ambiguous and unambiguous triplets we found equivalent priming strengths and patterns across the two visual fields, counter to the predictions of the coarse coding hypothesis. Priming patterns further suggested that both hemispheres made use of lexical level representations in the lexical decision task and semantic representations in the semantic judgment task.

Associative processing in the cerebral hemispheres was examined using ERPs and visual half-field (VF) methods. Associative strength was manipulated using asymmetrically associated pairs: viewed in one order (forward), there was a strong prime-to-target association, but in the backward order predictability was weak. N400 priming was greater for forward than backward pairs in both VFs and not different across VF, suggesting similar semantic representations and automatic meaning activation in the two hemispheres. However, a frontal P2 enhancement for forward pairs restricted to the LH suggests that it uses context to predict likely upcoming words. Also, greater late positive complex priming for backward pairs in the LH than the RH reveals a LH advantage for strategically reshaping meaning activation for weakly related and/or non-canonically ordered pairs. The results link asymmetries in word processing with those observed at the sentence level.

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.

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Previous work indicates mutual exclusivity in word learning in monolingual, but not bilingual toddlers. We asked whether this difference indicates distinct conceptual biases, or instead reflects best-guess heuristic use in the absence of context. We altered word-learning contexts by manipulating whether a familiar-or unfamiliarrace speaker introduced a novel word for an object with a known category label painted in a new color. Both monolingual and bilingual infants showed mutual exclusivity for a familiar-race speaker, and relaxed mutual exclusivity and treated the novel word as a category label for an unfamiliar-race speaker. Thus, monolingual and bilingual infants have access to similar word-learning heuristics, and both use nonlinguistic social context to guide their use of the most appropriate heuristic.

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