Infants' Perception of Intonation: Is It a Statement or a Question?

The ability to distinguish phonetic variations in speech that are relevant to meaning is essential for infants' language development. Previous studies into the acquisition of prosodic categories have focused on lexical stress, lexical pitch accent, or lexical tone. However, very little is known about the developmental course of infants' perception of linguistic intonation. In this study, we investigate infants' perception of the correlates of the statement/yes–no question contrast in a language that marks this sentence type distinction only by prosodic means, European Portuguese (EP). Using a modified version of the visual habituation paradigm, EP‐learning infants at 5–6 and 8–9 months were able to successfully discriminate segmentally varied, single‐prosodic word intonational phrases presented with statement or yes–no question intonation, demonstrating that they are sensitive to the prosodic cues marking this distinction as early as 5 months and maintain this sensitivity throughout the first year. These results suggest the presence of precocious discrimination abilities for intonation across segmental variation, similarly to previous reports for lexical pitch accent, but unlike previous findings for word stress.     

Infants' Listening Preferences: Baby Talk or Happy Talk?

The most robust finding on infants' listening preferences has been widely characterized as a preference for baby talk (BT) over adult‐directed speech (ADS). Although prosodic modifications characteristic of BT also convey positive affect, differences in affect across BT and ADS speech registers have not been controlled in previous studies. This set of experiments sought to elucidate the basis for 6‐month‐olds' listening preference by independently manipulating affect and speech register. When affect was held constant, no preference for any speech register was observed. Moreover, when ADS stimuli presented more positive affect than BT stimuli, infants' preferences followed the positive affect. Higher and more variable pitch was neither necessary nor sufficient for determining infants' preferences, although pitch characteristics may modulate affect‐based preferences. The BT preference is thus attributable to a more general preference for speech that imparts relatively positive affect, a preference perhaps ascribable to a preexisting general‐purpose mechanism opportunistically exploited by language.     

Changes in Preference for Infant‐Directed Speech in Low and Moderate Noise by 4.5‐ to 13‐Month‐Olds

Although a large literature discusses infants' preference for infant‐directed speech (IDS), few studies have examined how this preference might change over time or across listening situations. The work reported here compares infants' preference for IDS while listening in a quiet versus a noisy environment, and across 3 points in development: 4.5 months of age, 9 months of age, and 13 months of age. Several studies have suggested that IDS might help infants to pick out speech in the context of noise (Colombo, Frick, Ryther, Coldren, & Mitchell, 1995; Fernald, 1984; Newman, 2003); this might suggest that infants' preference for IDS would increase in these settings. However, this was not found to be the case; at all 3 ages, infants showed similar advantage (or lack thereof) for IDS as compared to adult‐directed speech when presented in noise versus silence. There was, however, a significant interaction across ages: Infants aged 4.5 months showed an overall preference for IDS, whereas older infants did not, despite listening to the same stimuli. The lack of an effect with older infants replicates and extends recent findings by Hayashi, Tamekawa, and Kiritani (2001), suggesting that the variations in fundamental frequency and affect are not sufficient cues to IDS for older infants.     

The Role of Verbal Repetition in the Development of Infant Speech Preferences From 4 to 14 Months of Age

Four experiments investigated infants' preferences for age‐appropriate and age‐inappropriate infant‐directed speech (IDS) over adult‐directed speech (ADS). Two initial experiments showed that 6‐, 10‐, and 14‐month‐olds preferred IDS directed toward younger infants, and 4‐, 8‐, 10‐, and 14‐month‐olds, but not 6‐month‐olds, preferred IDS directed toward older infants. In Experiment 3. 6‐month‐olds preferred IDS directed toward older infants when the frequency of repeated utterances matched IDS to younger infants. In Experiment 4, 6‐month‐olds preferred repeated IDS utterances over the same IDS utterances organized without repetition. Attention to repeated utterances precedes word segmentation and sensitivity to statistical cues in continuous speech, and might play a role in the discovery of these and other aspects of linguistic structure.     

Early Word Segmentation in Naturalistic Environments: Limited Effects of Speech Register

We examined 7.5‐month‐old infants' ability to segment words from infant‐ and adult‐directed speech (IDS and ADS). In particular, we extended the standard design of most segmentation studies by including a phase where infants were repeatedly exposed to target word recordings at their own home (extended exposure) in addition to a laboratory‐based familiarization. This enabled us to examine infants' segmentation of words from speech input in their naturalistic environment, extending current findings to learning outside the laboratory. Results of a modified preferential‐listening task show that infants listened longer to isolated tokens of familiarized words from home relative to novel control words regardless of register. However, infants showed no recognition of words exposed to during purely laboratory‐based familiarization. This indicates that infants succeed in retaining words in long‐term memory following extended exposure and recognizing them later on with considerable flexibility. In addition, infants segmented words from both IDS and ADS, suggesting limited effects of speech register on learning from extended exposure in naturalistic environments. Moreover, there was a significant correlation between segmentation success and infants' attention to ADS, but not to IDS, during the extended exposure phase. This finding speaks to current language acquisition models assuming that infants' individual attention to language stimuli drives successful learning.     

Parental Speech at 6 Months Predicts Joint Attention at 12 Months

In a prospective longitudinal study of a representative community sample (N = 264), mothers' references to infants' mental states were coded during a topic‐sharing task in the home at 6 months. Joint attention behaviour was assessed in the laboratory at 12 months. Individual joint attention skills (gaze following, gaze alternating, and declarative pointing) were significantly inter‐correlated, with a single factor accounting for 68% of the variance. Mothers' references to infants' mental states at 6 months predicted infants' joint attention at 12 months. The association was not explained by sociodemographic characteristics of the family, the mother's mental state, or by the quantity or acoustic properties of her speech. However, variability in pitch of maternal speech was an independent predictor of the infants' later joint attention skills. Taken together, these findings suggest that mothers' infant‐directed speech fosters infants' attentive participation in topic‐sharing interactions, which in turn provide an important arena in which joint attention skills develop over the first year of life.     

Six‐Month‐Olds' Detection of Clauses Embedded in Continuous Speech: Effects of Prosodic Well‐Formedness

Three experiments investigated the role of prosodic structure for infants' recognition of embedded word sequences. Six‐month‐olds were familiarized with 2 versions of the same sequence, 1 corresponding to a well‐formed prosodic unit and the other to a prosodically ill‐formed sequence (although a successive word series). Next, infants heard 2 test passages. One included the well‐formed unit, and the other included the ill‐formed sequence. In Experiment 1, infants listened longer to the passage containing the well‐formed unit, suggesting that such units, even when they are embedded, are better recognized. Experiments 2 and 3 showed that this better recognition does not depend on an acoustic match between the familiarized sequences and their later embeddings. This suggests that the advantage of the well‐formed unit is at least partially due to infants' use of prosody to parse continuous speech.     

Influences of Infant‐Directed Speech on Early Word Recognition

When addressing infants, many adults adopt a particular type of speech, known as infant‐directed speech (IDS). IDS is characterized by exaggerated intonation, as well as reduced speech rate, shorter utterance duration, and grammatical simplification. It is commonly asserted that IDS serves in part to facilitate language learning. Although intuitively appealing, direct empirical tests of this claim are surprisingly scarce. Additionally, studies that have examined associations between IDS and language learning have measured learning within a single laboratory session rather than the type of long‐term storage of information necessary for word learning. In this study, 7‐ and 8‐month‐old infants' long‐term memory for words was assessed when words were spoken in IDS and adult‐directed speech (ADS). Word recognition over the long term was successful for words introduced in IDS, but not for those introduced in ADS, regardless of the register in which recognition stimuli were produced. Findings are discussed in the context of the influence of particular input styles on emergent word knowledge in prelexical infants.     

Stress Pattern Preference in Spanish‐Learning Infants: The Role of Syllable Weight

As a result of exposure, infants acquire biases that conform to the rhythmic properties of their native language. Previous lexical stress preference studies have shown that English‐ and German‐, but not French‐learning infants, show a bias toward trochaic words. The present study explores Spanish‐learning infants' lexical stress preferential patterns and the role of syllable weight at 9 months of age. Spanish is a syllable‐timed language with no vowel reduction and variable stress. Around 50% of the word types in Spanish are disyllabic, with a superior proportion of trochees than iambs (60% and 40%, respectively). Experiment 1 with CV.CV pseudo‐words failed to reveal a clear trochaic bias in 9‐month‐old Spanish‐learning infants. However, when preference was explored with items containing a heavy syllable (CVC.CV and CV.CVC, respectively), both a trochaic (Experiment 2) and an iambic preference (Experiment 3) could be elicited. These results suggest that knowledge about the close and highly regular link between heavy syllables and stress assignment in Spanish can be easily acquired and determines infants' preference at 9 months of age, while for CV.CV items, the trochaic bias appears to be weak. Our results broaden the current knowledge on the factors that determine the emergence of rhythmic biases.     

Maternal input and infants’ response to infant‐directed speech

Caregivers typically use an exaggerated speech register known as infant‐directed speech (IDS) in communication with infants. Infants prefer IDS over adult‐directed speech (ADS) and IDS is functionally relevant in infant‐directed communication. We examined interactions among maternal IDS quality, infants’ preference for IDS over ADS, and the functional relevance of IDS at 6 and 13 months. While 6‐month‐olds showed a preference for IDS over ADS, 13‐month‐olds did not. Differences in gaze following behavior triggered by speech register (IDS vs. ADS) were found in both age groups. The degree of infants’ preference for IDS (relative to ADS) was linked to the quality of maternal IDS infants were exposed to. No such relationship was found between gaze following behavior and maternal IDS quality and infants’ IDS preference. The results speak to a dynamic interaction between infants’ preference for different kinds of social signals and the social cues available to them.     

Infant‐Directed Speech Is Modulated by Infant Feedback

When mothers engage in infant‐directed (ID) speech, their voices change in a number of characteristic ways, including adopting a higher overall pitch. Studies have examined these acoustical cues and have tested infants' preferences for ID speech. However, little is known about how these cues change with maternal sensitivity to infant feedback in the context of interaction. In this study, each mother watched her infant (located in an adjacent sound booth) on a video screen and talked to him or her through a microphone. The mother believed that her infant could hear her voice and she attempted to make her infant happy through her vocalizations. In reality, the infant could not hear her voice. The mother's ID speech was analyzed in real time for changes in mean pitch. For half of the infant–mother dyads an experimenter surreptitiously positively engaged the infant when the voice analysis revealed a rise in pitch, thereby producing positive reinforcement to the mother for natural higher pitched ID speech. The other half were reinforced for lower pitched ID speech. Mothers raised their pitch significantly more in the former than the latter condition, illustrating that the pitch of ID speech is dynamically affected by feedback from the infant.     

Chinese and English Infants' Tone Perception: Evidence for Perceptual Reorganization

Over half the world's population speaks a tone language, yet infant speech perception research has typically focused on consonants and vowels. Very young infants can discriminate a wide range of native and nonnative consonants and vowels, and then in a process of perceptual reorganization over the 1st year, discrimination of most nonnative speech sounds deteriorates. We investigated perceptual reorganization for tones by testing 6‐ and 9‐month‐old infants from tone (Chinese) and nontone (English) language environments for speech (lexical tone) and nonspeech (violin sound) tone discrimination in both cross‐sectional and longitudinal studies. Overall, Chinese infants performed equally well at 6 and 9 months for both speech and nonspeech tone discrimination. Conversely, English infants' discrimination of lexical tone declined between 6 and 9 months of age, whereas their nonspeech tone discrimination remained constant. These results indicate that the reorganization of tone perception is a function of the native language environment, and that this reorganization is linguistically based. Supplementary materials to this article are available on the World Wide Web at http:www.infancyarchives.com     

The role of prosody in infants’ preference for speech: A comparison between speech and birdsong

Speech preferences emerge very early in infancy, pointing to a special status for speech in auditory processing and a crucial role of prosody in driving infant preferences. Recent theoretical models suggest that infant auditory perception may initially encompass a broad range of human and nonhuman vocalizations, then tune in to relevant sounds for the acquisition of species‐specific communication sounds. However, little is known about sound properties eliciting infants’ tuning‐in to speech. To address this issue, we presented a group of 4‐month‐olds with segments of non‐native speech (Mandarin Chinese) and birdsong, a nonhuman vocalization that shares some prosodic components with speech. A second group of infants was presented with the same segment of birdsong paired with Mandarin played in reverse. Infants showed an overall preference for birdsong over non‐native speech. Moreover, infants in the Backward condition preferred birdsong over backward speech whereas infants in the Forward condition did not show clear preference. These results confirm the prominent role of prosody in early auditory processing and suggest that infants’ preferences may privilege communicative vocalizations featured by certain prosodic dimensions regardless of the biological source of the sound, human or nonhuman.     

Attention to Maternal Multimodal Naming by 6‐ to 8‐Month‐Old Infants and Learning of Word–Object Relations

We examined whether mothers' use of temporal synchrony between spoken words and moving objects, and infants' attention to object naming, predict infants' learning of word–object relations. Following 5 min of free play, 24 mothers taught their 6‐ to 8‐month‐olds the names of 2 toy objects, Gow and Chi, during a 3‐min play episode. Infants were then tested for their word mapping. The videotaped episodes were coded for mothers' object naming and infants' attention to different naming types. Results indicated that mothers' use of temporal synchrony and infants' attention during play covaried with infants' word‐mapping ability. Specifically, infants who switched eye gaze from mother to object most frequently during naming learned the word–object relations. The findings suggest that maternal naming and infants' word‐mapping abilities are bidirectionally related. Variability in infants' attention to maternal multimodal naming explains the variability in early lexical‐mapping development.     

Infant‐Directed Prosody Helps Infants Map Sounds to Meanings

Adults typically use an exaggerated, distinctive speaking style when addressing infants. However, the effects of infant‐directed (ID) speech on infants' learning are not yet well understood. This research investigates how ID speech affects how infants perform a key function in language acquisition, associating the sounds of words with their meanings. Seventeen‐month‐old infants were presented with two label‐object pairs in a habituation‐based word learning task. In Experiment 1, the labels were produced in adult‐directed (AD) speech. In Experiment 2, the labels were produced in ID prosody; they had higher pitch, greater pitch variation, and longer durations than the AD labels. We found that infants failed to learn the labels in AD speech, but succeeded in learning the same labels when they were produced in ID speech. Experiment 3 investigated the role of variability in learning from ID speech. When the labels were presented in ID prosody with no variation across tokens, infants failed to learn them. Our findings indicate that ID prosody can affect how readily infants map sounds to meanings and that the variability in prosody that is characteristic of ID speech may play a key role in its effect on learning new words.     

Face Preferences for Infant‐ and Adult‐Directed Speakers in Infants of Depressed and Nondepressed Mothers: Association with Infant Cognitive Development

Face preferences for speakers of infant‐directed and adult‐directed speech (IDS and ADS) were investigated in 4‐ to 13.5‐month‐old infants of depressed and nondepressed mothers. Following 1 min of exposure to an ID or AD speaker (order counterbalanced), infants had an immediate paired‐comparison test with a still, silent image of the familiarized versus a novel face. In the test phase, ID face preference ratios were significantly lower in infants of depressed than nondepressed mothers. Infants' ID face preference ratios, but not AD face preference ratios, correlated with their percentile scores on the cognitive (Cog) scale of the Bayley Scales of Infant & Toddler Development (3rd Edition; BSID‐III), assessed concurrently. Regression analyses revealed that infant ID face preferences significantly predicted infant Cog percentiles even after demographic risk factors and maternal depression had been controlled. Infants may use IDS to select social partners who are likely to support and facilitate cognitive development.     

Infant‐Directed Speech Facilitates Word Segmentation

There are reasons to believe that infant‐directed (ID) speech may make language acquisition easier for infants. However, the effects of ID speech on infants' learning remain poorly understood. The experiments reported here assess whether ID speech facilitates word segmentation from fluent speech. One group of infants heard a set of nonsense sentences spoken with intonation contours characteristic of adult‐directed (AD) speech, and the other group heard the same sentences spoken with intonation contours characteristic of ID speech. In both cases, the only cue to word boundaries was the statistical structure of the speech. Infants were able to distinguish words from syllable sequences spanning word boundaries after exposure to ID speech but not after hearing AD speech. These results suggest that ID speech facilitates word segmentation and may be useful for other aspects of language acquisition as well. Issues of direction of preference in preferential listening paradigms are also considered.     

The Use of Pitch Accent in Word–Object Association by Monolingual Japanese Infants

This study investigated the lexical use of Japanese pitch accent in Japanese‐learning infants. A word–object association task revealed that 18‐month‐old infants succeeded in learning the associations between two nonsense objects paired with two nonsense words minimally distinguished by pitch pattern (Experiment 1). In contrast, 14‐month‐old infants failed (Experiment 2). Eighteen‐month‐old infants succeeded even for sounds that contained only the prosodic information (Experiment 3). However, a subsequent experiment revealed that 14‐month‐old infants succeeded in an easier single word–object task using pitch contrast (Experiment 4). These findings indicate that pitch pattern information is robustly available to 18‐month‐old Japanese monolingual infants in a minimal pair word‐learning situation, but only partially accessible in the same context for 14‐month‐old infants.     

Clause Segmentation by 6‐Month‐Old Infants: A Crosslinguistic Perspective

Each clause and phrase boundary necessarily aligns with a word boundary. Thus, infants' attention to the edges of clauses and phrases may help them learn some of the language‐specific cues defining word boundaries. Attention to prosodically well‐formed clauses and phrases may also help infants begin to extract information important for learning the grammatical structure of their language. Despite the potentially important role that the perception of large prosodic units may play in early language acquisition, there has been little work investigating the extraction of these units from fluent speech by infants learning languages other than English. We report 2 experiments investigating Dutch learners' clause segmentation abilities. In these studies, Dutch‐learning 6‐month‐olds readily extract clauses from speech. However, Dutch learners differ from English learners in that they seem to be more reliant on pauses to detect clause boundaries. Two closely related explanations for this finding are considered, both of which stem from the acoustic differences in clause boundary realizations in Dutch versus English.     

Acoustic Packaging of Action Sequences by Infants

This study investigated whether acoustic input, in the form of infant‐directed speech, influenced infants' segmenting of action sequences. Thirty‐two 7.5‐ to 11.5‐month‐old infants were familiarized with video sequences made up of short action clips. Narration coincided with portions of the action stream to package certain pairs of clips together. At test, packaged and nonpackaged pairs of actions were presented side by side in silence. Narration heard during familiarization influenced how infants viewed the action units, such that at test, infants older than 9.5 months (but not younger) looked longer at the nonpackaged than the packaged action sequences. The role of infant‐directed speech as well as other types of acoustic input in assisting infants' processing of action is discussed.