Electrophysiological evidence for the understanding of maternal speech by 9-month-old infants

Early word learning in infants relies on statistical, prosodic, and social cues that support speech segmentation and the attachment of meaning to words. It is debated whether such early word knowledge represents mere associations between sound patterns and visual object features, or reflects referential understanding of words. By measuring an event-related brain potential component known as the N400, we demonstrated that 9-month-old infants can detect the mismatch between an object appearing from behind an occluder and a preceding label with which their mother introduces it. Differential N400 amplitudes have been shown to reflect semantic priming in adults, and its absence in infants has been interpreted as a sign of associative word learning. By setting up a live communicative situation for referring to objects, we demonstrated that a similar priming effect also occurs in young infants. This finding may indicate that word meaning is referential from the outset of word learning and that referential expectation drives, rather than results from, vocabulary acquisition in humans.     

Signature tunes in mothers' speech to infants

The purpose of the present investigation was to determine whether mothers use discernible tunes (i.e., specific interval sequences) in their speech to infants and whether such tunes are individually distinctive. Mothers were recorded speaking with their infants on two occasions separated by 1 week or more. Examination of the tunes of each mother revealed discernible tunes and frequent repetitions of tunes within and across sessions. Comparisons of utterances with the most common pitch contour (i.e., rising), both within and across mothers, revealed interval patterns that were individually distinctive, or unique. The findings confirm the prominence of tunes and the presence of signature tunes in maternal speech to infants.     

The roles of letter names and letter sounds in connecting print and speech

Three experiments were carried out to examine the cues that are used in learning to read and spell new words. In a reading task (Experiment 1), even preschoolers who could not read simple real words were able to benefit from print-sound relationships that were based on letter names. They found it easier to learn that the made-up word TM was pronounced as 'team" (name condition) than that TM was pronounced as "tame" (sound condition) or as "wide" (visual condition). The letter-name strategy persisted among college students (Experiment 2). In a spelling task (Experiment 3), prereaders and novice readers again did better in the name condition than in the sound condition. The ability to use relationships based on letter sounds emerged later than the ability to use relationships based on letter names. However, sound-based relationships were used to a greater extent in spelling than in reading.     

Fathers' and mothers' speech to young infants

Fathers' and mothers' speech to infants was obtained during face-to-face interaction in a laboratory setting. Thirty-two father-infant pairs and 40 mother-infant pairs participated. Infants were divided equally by sex and among two age groups with mean ages of 3 and 9 months. Parental utterances were transcribed from videotapes. The utterances were analyzed in terms of their structure and content. There were many similarities in the structure of fathers' and mothers' speech. The speech of both parents was highly repetitive and contained many questions. There were also similarities in the content of fathers' and mothers' speech. Their belief in the infants' ability to think, feel, and act like persons was evident in their speech to the infants. The age of the infant was a significant factor in the analysis of many of the content categories. The sex of the infant and the sex of the parent were also significant factors in several of the analyses.This paper is based on a thesis submitted by the first author in partial fulfillment of the requirements for a master's degree. Some of the data reported here were obtained under a grant from the Spencer Foundation to the second author.     

Infants’ responsiveness to maternal speech and singing

Infants who were 6 months of age were presented with extended audiovisual episodes of their mother's infant-directed speech or singing. Cumulative visual fixation and initial fixation of the mother's image were longer for maternal singing than for maternal speech. Moreover, movement reduction, which may signal intense engagement, accompanied visual fixation more frequently for maternal singing than for maternal speech. The stereotypy and repetitiveness of maternal singing may promote moderate arousal levels, which sustain infant attention, in contrast to the greater variability of speech, which may result in cycles of heightened arousal, gaze aversion, and re-engagement. The regular pulse of music may also enhance emotional coordination between mother and infant.     

How infants begin to extract words from speech

A crucial step for acquiring a native language vocabulary is the ability to segment words from fluent speech. English-learning infants first display some ability to segment words at about 7.5 months of age. However, their initial attempts at segmenting words only approximate those of fluent speakers of the language. In particular, 7.5-month-old infants are able to segment words that conform to the predominant stress pattern of English words. The ability to segment words with other stress patterns appears to require the use of other sources of information about word boundaries. By 10.5 months, English learners display sensitivity to additional cues to word boundaries such as statistical regularities, allophonic cues and phonotactic patterns. Infants’ word segmentation abilities undergo further development during their second year when they begin to link sound patterns with particular meanings. By 24 months, the speed and accuracy with which infants recognize words in fluent speech is similar to that of native adult listeners. This review describes how infants use multiple sources of information to locate word boundaries in fluent speech, thereby laying the foundations for language understanding.     

Visual speech contributes to phonetic learning in 6-month-old infants

Previous research has shown that infants match vowel sounds to facial displays of vowel articulation [Kuhl, P. K., & Meltzoff, A. N. (1982). The bimodal perception of speech in infancy. Science, 218, 1138–1141; Patterson, M. L., & Werker, J. F. (1999). Matching phonetic information in lips and voice is robust in 4.5-month-old infants. Infant Behaviour & Development, 22, 237–247], and integrate seen and heard speech sounds [Rosenblum, L. D., Schmuckler, M. A., & Johnson, J. A. (1997). The McGurk effect in infants. Perception & Psychophysics, 59, 347–357; Burnham, D., & Dodd, B. (2004). Auditory-visual speech integration by prelinguistic infants: Perception of an emergent consonant in the McGurk effect. Developmental Psychobiology, 45, 204–220]. However, the role of visual speech in language development remains unknown. Our aim was to determine whether seen articulations enhance phoneme discrimination, thereby playing a role in phonetic category learning. We exposed 6-month-old infants to speech sounds from a restricted range of a continuum between /ba/ and /da/, following a unimodal frequency distribution. Synchronously with these speech sounds, one group of infants (the two-category group) saw a visual articulation of a canonical /ba/ or /da/, with the two alternative visual articulations, /ba/ and /da/, being presented according to whether the auditory token was on the /ba/ or /da/ side of the midpoint of the continuum. Infants in a second (one-category) group were presented with the same unimodal distribution of speech sounds, but every token for any particular infant was always paired with the same syllable, either a visual /ba/ or a visual /da/. A stimulus-alternation preference procedure following the exposure revealed that infants in the former, and not in the latter, group discriminated the /ba/–/da/ contrast. These results not only show that visual information about speech articulation enhances phoneme discrimination, but also that it may contribute to the learning of phoneme boundaries in infancy.     

Mothers' and fathers' speech to infants in a teaching situation

The purpose of this study was to compare mothers' and fathers' speech to their preverbal infants in a teaching situation. Thirty-two parents of 16 8-month-olds were asked to teach their infants to put a small cube into a cup. Infant Gender (2) x Birth Order (2) x Parent (2) analyses of variance were performed with repeated measures on parent. Results indicated that fathers issued more utterances and used more words per utterance than did mothers. Although there was no difference in the proportion of imperatives used by mothers and fathers, fathers' imperatives were significantly longer than mothers'; this difference was not evident for utterances that contained indirect instructions. Mothers tended to use more exact repetitions. There were differences in parental speech related to infant gender: Parents directed more utterances, particularly utterances that contained negative statements, imperatives, and exhortations, to girls than to boys. Infant Gender x Parent effects for imperatives and exhortations indicated that these differences were especially true for fathers. Overall, it appeared that fathers made greater efforts to control the situation and to direct their infants' behavior, which might have reflected mothers' and fathers' different perceptions of both their infants' ability and their own role as teachers.     

Acoustic determinants eliciting Japanese infants' vocal response to maternal speech

Generally, infants prefer infant-directed speech to adult-directed speech. This study investigated which acoustic features of maternal infant-directed speech elicit effectively 3-mo.-old infants' vocal response. The participants were 40 Japanese mother and infant dyads. Vocal f0 from the mother's speech and the infant's vocalization was extracted using Computerized Speech Laboratory (CSL4300) and custom software. The acoustical features measured were mean fundamental frequency (f0), and f0 contour. The rate of the infant's vocal response was significantly higher When the maternal infant-directed speech was terminated with a falling contour rather than a rising or flat contour. There was no significant difference between the mean f0 of the maternal infant-directed speech followed or not followed by the infant's vocal response. This suggests that the falling contour of terminal maternal infant-directed speech serves to elicit the 3-mo.-old infant's vocal response.     

Object names and object functions serve as cues to categories for infants

Can object names and functions act as cues to categories for infants? In Study 1, 14- and 18-month-old infants were shown novel category exemplars along with a function, a name, or no cues. Infants were then asked to "find another one," choosing between 2 novel objects (1 from the familiar category and the other not). Infants at both ages were more likely to select the category match in the function than in the no-cue condition. However, only at 18 months did naming the objects enhance categorization. Study 2 shows that names can facilitate categorization for 14-month-olds as well when a hint regarding the core meaning of the objects (the function of a single familiarization object) is provided.     

Converging measures of speech segmentation in preverbal infants

Two studies using novel extensions of the conditioned head-turning method examined contributions of rhythmic and distributional properties of syllable strings to 8-month-old infants' speech segmentation. The two techniques introduced exploit fundamental, but complementary, properties of representational units. The first involved assessment of discriminative response maintenance when simple training stimuli were embedded in more complex speech contexts; the second involved measurement of infants' latencies in detecting extraneous signals superimposed on speech stimuli. A complex pattern of results is predicted if infants succeed in grouping syllables into higher-order units. Across the two studies, the predicted pattern of results emerged, indicating that rhythmic properties of speech play an important role in guiding infants toward potential linguistically relevant units and simultaneously demonstrating that the techniques proposed here provide valid, converging measures of infants' auditory representational units.     

Didactic adjustments in fathers' and mothers' speech to their 3-month-old infants

Vocal dialogues of 3-month-old infants with their mothers and fathers were recorded during dyadic interactions in the laboratory. Six-minute speech samples were analyzed for syntacticlexical and temporal-melodic features. Both parents adopted strikingly similar speech registers. Segmentation, reduction in syntactic complexity, repetitiveness, and slow tempo were more marked than reported for parental speech to children above 1 year. However, rather than providing proper linguistic models, parents utilized simplified patterns of expressive melodic contours as the most salient units of speech. This tendency is interpretable as age-specific adjustment to infants' integrative capacities. Structural similarities between maternal and paternal baby talk by far outweighed a few quantitative differences. The intuitive nature of recourse to basic nonverbal properties of vocal communication, together with universality across sex, favors the assumption that baby talk is a part of species-specific didactic support to infant communicative development.     

The effect of selective adaptation on the identification of speech sounds

An experiment was performed to determine the effect of selective adaptation on the identification of synthetic speech sounds which varied along the phonetic dimensionplace of articulation. Adaptation with a stimulus of a particular place value led to a reduction in the number of test stimuli identified as having that place value. An identification shift was obtained even when the acoustic information specifying place value for the adapting stimulus had virtually nothing in common with the information specifying place value for any of the test stimuli. Removing the vowel portion of an adapting stimulus eliminated identification shift only when the resulting stimulus was no longer perceived as speech-like. The results indicate that at least part of the adaptation effect occurs at a site of phonetic, not merely acoustic, feature analysis.

     

Language identification from visual-only speech signals

Our goal in the present study was to examine how observers identify English and Spanish from visual-only displays of speech. First, we replicated the recent findings of Soto-Faraco et al. (2007) with Spanish and English bilingual and monolingual observers using different languages and a different experimental paradigm (identification). We found that prior linguistic experience affected response bias but not sensitivity (Experiment 1). In two additional experiments, we investigated the visual cues that observers use to complete the languageidentification task. The results of Experiment 2 indicate that some lexical information is available in the visual signal but that it is limited. Acoustic analyses confirmed that our Spanish and English stimuli differed acoustically with respect to linguistic rhythmic categories. In Experiment 3, we tested whether this rhythmic difference could be used by observers to identify the language when the visual stimuli is temporally reversed, thereby eliminating lexical information but retaining rhythmic differences. The participants performed above chance even in the backward condition, suggesting that the rhythmic differences between the two languages may aid language identification in visual-only speech signals. The results of Experiments 3A and 3B also confirm previous findings that increased stimulus length facilitates language identification. Taken together, the results of these three experiments replicate earlier findings and also show that prior linguistic experience, lexical information, rhythmic structure, and utterance length influence visual-only language identification.     

Pi ka pu: The perception of speech sounds by prelinguistic infants

Attention, Perception, & Psychophysics - Experimentation with 14–18-week-old infants indicates that they are capable of grouping together syllables of English depending on whether the...     

Studies on the categorization of speech by infants

It is well-known that complexities exist in the mapping between the acoustic information in the speech signal and the phonetic categories of adult language users. We investigated whether the same complexities exist in the mapping between the speech signal and the forerunners of these categories in infants. For two classes of complexity, we found that the manner in which the categorization of information for speech occurs was virtually identical in infant and adult listeners. These findings indicate that the infant possesses finely tuned linguistically-relevant perceptual abilities, which undoubtedly facilitate and shape the task of language acquisition.