Alejandrina Cristia

Cerebral lateralization and early speech acquisition: A developmental scenario

During the past ten years, research using Near-infrared Spectroscopy (NIRS) to study the developing brain has provided groundbreaking evidence of brain functions in infants. This paper presents a theoretically oriented review of this wealth of evidence, summarizing recent NIRS data on language processing, without neglecting other neuroimaging or behavioral studies in infancy and adulthood. We review three competing classes of hypotheses (i.e. signal-driven, domain-driven, and learning biases hypotheses) regarding the causes of hemispheric specialization for speech processing. We assess the fit between each of these hypotheses and neuroimaging evidence in speech perception and show that none of the three hypotheses can account for the entire set of observations on its own. However, we argue that they provide a good fit when combined within a developmental perspective. According to our proposed scenario, lateralization for language emerges out of the interaction between pre-existing left-right biases in generic auditory processing (signal-driven hypothesis), and a left-hemisphere predominance of particular learning mechanisms (learning-biases hypothesis). As a result of this completed developmental process, the native language is represented in the left hemisphere predominantly. The integrated scenario enables to link infant and adult data, and points to many empirical avenues that need to be explored more systematically.

Linguistic Processing of Accented Speech Across the Lifespan

In most of the world, people have regular exposure to multiple accents. Therefore, learning to quickly process accented speech is a prerequisite to successful communication. In this paper, we examine work on the perception of accented speech across the lifespan, from early infancy to late adulthood. Unfamiliar accents initially impair linguistic processing by infants, children, younger adults, and older adults, but listeners of all ages come to adapt to accented speech. Emergent research also goes beyond these perceptual abilities, by assessing links with production and the relative contributions of linguistic knowledge and general cognitive skills. We conclude by underlining points of convergence across ages, and the gaps left to face in future work.

Allophonic and Phonemic Contrasts in Infants' Learning of Sound Patterns

French-learning 11-month-old and English-learning 11- and 4-month-old infants were familiarized with consonant–vowel–consonant syllables in which the final consonants were dependent on whether the preceding vowel was oral or nasal. Oral and nasal vowels are present in the ambient language of all participants, but vowel nasality is phonemic (contrastive) in French and allophonic (noncontrastive) in English. After familiarization, infants heard novel syllables that either followed or violated the familiarized patterns. French-learning 11-month-olds and English-learning 4-month-olds displayed a reliable pattern of preference demonstrating learning and generalization of the patterns, while English-learning 11-month-olds oriented equally to syllables following and violating the familiarized patterns. The results are consistent with an experience-driven reduction of attention to allophonic contrasts by as early as 11 months, which influences phonotactic learning.

The hyperarticulation hypothesis of infant-directed speech

Typically, the point vowels [i,ɑ,u] are acoustically more peripheral in infant-directed speech (IDS) compared to adult-directed speech (ADS). If caregivers seek to highlight lexically relevant contrasts in IDS, then two sounds that are contrastive should become more distinct, whereas two sounds that are surface realizations of the same underlying sound category should not. To test this prediction, vowels that are phonemically contrastive ([i-ɪ] and [eɪ-ε]), vowels that map onto the same underlying category ([æ- ] and [ε- ]), and the point vowels [i,ɑ,u] were elicited in IDS and ADS by American English mothers of two age groups of infants (four- and eleven-month-olds). As in other work, point vowels were produced in more peripheral positions in IDS compared to ADS. However, there was little evidence of hyperarticulation per se (e.g. [i-ɪ] was hypoarticulated). We suggest that across-the-board lexically based hyperarticulation is not a necessary feature of IDS.

Toddlers recognize words in an unfamiliar accent after brief exposure

Both subjective impressions and previous research with monolingual listeners suggest that a foreign accent interferes with word recognition in infants, young children, and adults. However, because being exposed to multiple accents is likely to be an everyday occurrence in many societies, it is unexpected that such non-standard pronunciations would significantly impede language processing once the listener has experience with the relevant accent. Indeed, we report that 24-month-olds successfully accommodate an unfamiliar accent in rapid word learning after less than 2 minutes of accent exposure. These results underline the robustness of our speech perception mechanisms, which allow listeners to adapt even in the absence of extensive lexical knowledge and clear known-word referents.

Mothers Speak Less Clearly to Infants Than to Adults A Comprehensive Test of the Hyperarticulation Hypothesis

Infants learn language at an incredible speed, and one of the first steps in this voyage is learning the basic sound units of their native languages. It is widely thought that caregivers facilitate this task by hyperarticulating when speaking to their infants. Using state-of-the-art speech technology, we addressed this key theoretical question: Are sound categories clearer in infant-directed speech than in adult-directed speech? A comprehensive examination of sound contrasts in a large corpus of recorded, spontaneous Japanese speech demonstrates that there is a small but significant tendency for contrasts in infant-directed speech to be less clear than those in adult-directed speech. This finding runs contrary to the idea that caregivers actively enhance phonetic categories in infant-directed speech. These results suggest that to be plausible, theories of infants’ language acquisition must posit an ability to learn from noisy data.

Parental Reports on Touch Screen Use in Early Childhood

Touch screens are increasingly prevalent, and anecdotal evidence suggests that young children are very drawn towards them. Yet there is little data regarding how young children use them. A brief online questionnaire queried over 450 French parents of infants between the ages of 5 and 40 months on their young child’s use of touch-screen technology. Parents estimated frequency of use, and further completed several checklists. Results suggest that, among respondent families, the use of touch screens is widespread in early childhood, meaning that most children have some exposure to touch screens. Among child users, certain activities are more frequently reported to be liked than others, findings that we discuss in light of current concern for children’s employment of time and the cognitive effects of passive media exposure. Additionally, these parental reports point to clear developmental trends for certain types of interactive gestures. These results contribute to the investigation of touch screen use on early development and suggest a number of considerations that should help improve the design of applications geared towards toddlers, particularly for scientific purposes.

Perceptual attunement in vowels: A meta-analysis

Although the majority of evidence on perceptual narrowing in speech sounds is based on consonants, most models of infant speech perception generalize these findings to vowels, assuming that vowel perception improves for vowel sounds that are present in the infants native language within the first year of life, and deteriorates for non-native vowel sounds over the same period of time. The present meta-analysis contributes to assessing to what extent these descriptions are accurate in the first comprehensive quantitative meta-analysis of perceptual narrowing in infant vowel discrimination, including results from behavioral, electrophysiological, and neuroimaging methods applied to infants 0-14 months of age. An analysis of effect sizes for native and non-native vowel discrimination over the first year of life revealed that they changed with age in opposite directions, being significant by about 6 months of age.

Predicting individual variation in language from infant speech perception measures

There are increasing reports that individual variation in behavioral and neurophysiological measures of infant speech processing predicts later language outcomes, and specifically concurrent or subsequent vocabulary size. If such findings are held up under scrutiny, they could both illuminate theoretical models of language development and contribute to the prediction of communicative disorders. A qualitative, systematic review of this emergent literature illustrated the variety of approaches that have been used and highlighted some conceptual problems regarding the measurements. A quantitative analysis of the same data established that the bivariate relation was significant, with correlations of similar strength to those found for well-established nonlinguistic predictors of language. Further exploration of infant speech perception predictors, particularly from a methodological perspective, is recommended.

An online database of infant functional near infrared spectroscopy studies: a community-augmented systematic review.

Until recently, imaging the infant brain was very challenging. Functional Near InfraRed Spectroscopy (fNIRS) is a promising, relatively novel technique, whose use is rapidly expanding. As an emergent field, it is particularly important to share methodological knowledge to ensure replicable and robust results. In this paper, we present a community-augmented database which will facilitate precisely this exchange. We tabulated articles and theses reporting empirical fNIRS research carried out on infants below three years of age along several methodological variables. The resulting spreadsheet has been uploaded in a format allowing individuals to continue adding new results, and download the most recent version of the table. Thus, this database is ideal to carry out systematic reviews. We illustrate its academic utility by focusing on the factors affecting three key variables: infant attrition, the reliability of oxygenated and deoxygenated responses, and signal-to-noise ratios. We then discuss strengths and weaknesses of the DBIfNIRS, and conclude by suggesting a set of simple guidelines aimed to facilitate methodological convergence through the standardization of reports.