Christine Kitamura

Universality and specificity in infant-directed speech : pitch modifications as a function of infant age and sex in a tonal and non-tonal language

The aim of this study was to investigate the prosodic characteristics of infant-directed speech (IDS) to boys and girls in a tonal (Thai) and non-tonal (Australian English) language. Speech was collected from mothers speaking to infants at birth, and 3, 6, 9, and 12 months, and also to another adult. Mean-F0, pitch range, and utterance slope-F0 were extracted, and the integrity of the tonal information in Thai investigated. The age trends across the two languages differed for each of these measures but Australian English IDS was generally more exaggerated than Thai IDS. With respect to sex differences, Australian English mothers used higher mean-F0, pitch range, and more rising utterances for girls than boys, but Thai mothers used more subdued mean-F0 and more falling utterances for girls than boys. Despite variations in pitch modifications by Thai and Australian English mothers, overall IDS is more exaggerated than adult-directed speech (ADS) in both languages. Furthermore, tonal information in Thai was only slightly less identifiable in Thai IDS than Thai ADS. The universal features and language-specific differences in IDS are discussed in terms of facilitating infant socialization at younger ages, and language acquisition later in infancy.

Motherese by Eye and Ear: Infants Perceive Visual Prosody in Point-Line Displays of Talking Heads

Infant-directed (ID) speech provides exaggerated auditory and visual prosodic cues. Here we investigated if infants were sensitive to the match between the auditory and visual correlates of ID speech prosody. We presented 8-month-old infants with two silent line-joined point-light displays of faces speaking different ID sentences, and a single vocal-only sentence matched to one of the displays. Infants looked longer to the matched than mismatched visual signal when full-spectrum speech was presented; and when the vocal signals contained speech low-pass filtered at 400 Hz. When the visual display was separated into rigid (head only) and non-rigid (face only) motion, the infants looked longer to the visual match in the rigid condition; and to the visual mismatch in the non-rigid condition. Overall, the results suggest 8-month-olds can extract information about the prosodic structure of speech from voice and head kinematics, and are sensitive to their match; and that they are less sensitive to the match between lip and voice information in connected speech.

Magnitude of phonetic distinction predicts success at early word learning in native and non-native accents

Although infants perceptually attune to native vowels and consonants well before 12 months, at 13–15 months, they have difficulty learning to associate novel words that differ by their initial consonant (e.g., BIN and DIN) to their visual referents. However, this difficulty may not apply to all minimal pair novel words. While Canadian English (CE) 15-month-olds failed to respond to a switch from the newly learned word DEET to the novel non-word DOOT, they did notice a switch from DEET to DIT (Curtin et al., 2009). Those authors argued that early word learners capitalize on large phonetic differences, seen in CE DEET–DIT, but not on smaller phonetic differences, as in CE DEET–DOOT. To assess this hypothesis, we tested Australian English (AusE) 15-month-olds, as AusE has a smaller magnitude of phonetic difference in both novel word pairs. Two groups of infants were trained on the novel word DEET and tested on the vowel switches in DIT and DOOT, produced by an AusE female speaker or the same CE female speaker as in Curtin et al. (2009). If the size of the phonetic distinction plays a more central role than native accent experience in early word learning, AusE children should more easily recognize both of the unfamiliar but larger CE vowel switches than the more familiar but smaller AusE ones. The results support our phonetic-magnitude hypothesis: AusE children taught and tested with the CE-accented novel words looked longer to both of the switch test trials (DIT, DOOT) than same test trials (DEET), while those who heard the AusE-accented tokens did not notice either switch. Implications of our findings for models of early word learning are discussed.

Aussie, Aussie, Aussie, Oi‐Oi‐Oi: Infants love an Australian accent

This study examines infant’s attention to dialect differences following Nazzi et al.’s [J. Mem. Lang., 43, 1–19 (2000)] finding that American 5‐month‐olds can discriminate British‐ and American‐English. Using a serial preference task, 48 6‐month‐old Australian and American infants heard sentence sets spoken in Australian‐ and American‐English. Results showed that at 6 months, American infants listen longer to Australian than American sentences, but Australian infants show no preference. By 8 months, American infants also show no preference. The developmental lag suggests Australian infants have more exposure to the American dialect (e.g., television programs) than American infants to the Australian dialect. Thus, it is predicted, with less linguistic experience, Australian 3‐month‐olds will show a dialect preference comparable to American 6‐month‐olds. Data from 14 3‐month‐olds support this hypothesis; moreover, they also listen longer to Australian than American sentences. Together the results imply that...

On the rhythm of infant- versus adult-directed speech in Australian English

The findings are reported of an investigation into rhythmic differences between infant-directed speech (IDS) and adult-directed speech (ADS) in a corpus of utterances from Australian English mothers speaking to their infants and to another adult. Given the importance of rhythmic cues to stress and word-segmentation in English, the investigation focused on the extent to which IDS makes such cues salient. Two methods of analysis were used: one focused on segmental durational properties, using a variety of durational measures; the other focused on the prominence of vocalic/sonorant segments, as determined by their duration, intensity, pitch, and spectral balance, using individual measures as well as composite measures of prominence derived from auditory-model analyses. There were few IDS/ADS differences/trends on the individual measures, though mean pitch and pitch variability were higher in IDS than ADS, while IDS vowels showed more negative spectral tilt. However, the model-based analyses suggested that differences in the prominence of vowels/sonorant segments were reduced in IDS, with further analysis suggesting that pitch contributed little to prominence. The reduction in prominence contrasts may be due to the importance of mood-regulation in speech to young infants, and may suggest that infants rely on segmental cues to stress and word-segmentation.

Infant‐directed speech to infants with a simulated hearing loss.

The acoustic/phonetic features of infant‐directed speech (IDS) were measured during face‐to‐face interactions between mothers and their six‐month‐old normal hearing infants (N=32) using a setup in which the mother and infant are seated in separate rooms and interact over their respective video monitors. There were two sound conditions, (i) a hearing condition in which infants could hear their mothers at 55 dB SPL, and (ii) a hearing loss condition in which the sound was turned off, and the infants could not hear their mothers. All mothers were told your baby cannot hear you. Mothers and infants interacted for 10 min using three labeled toys (sheep, shoe, and shark) to facilitate the production of exemplars of the corner vowels /i/, /u/, and /a/. The results showed that mean fundamental frequency (F0), F0 range, and the duration of the IDS vowels were comparable across the two conditions. However, vowel hyperarticulation was only evident in the hearing condition, not in the hearing loss condition. These re...

Communicative intent and affect in mothers’ speech to hearing-impaired infants with cochlear implants

Emotional properties of infant-directed speech influence normal-hearing (NH) infants’ attention to speech sounds. The current study examines communicative intent/affect in speech to hearing-impaired (HI) infants following the first year of cochlear implantation. Mothers of HI infants (HI group, ages 13.3—25.5 months), NH age-matched infants (NH-AM group, ages 13.5—25.7 months) and NH experience-matched infants (NH-EM group, ages 2.3—3.6 months) were recorded playing with their infants at three sessions over the course of one year. 25-second speech samples were low-pass filtered, leaving pitch but not speech information intact. Twelve adults rated stimuli along five scales of communicative intent/affect: Positive/Negative Affect, Intention to Express Affection, Encourage Attention, Comfort/Sooth and Direct Behavior. ANOVAs demonstrated main effects of Group and/or Session for all scales (ps = 0.01 to 0.07). Speech to HI and NH-EM infants was more positive, affective, encouraging, and comforting than speech...

Modified spectral tilt affects infants' native-language discrimination of approximants and vowels.

This studys aim was to determine if 6- and 9-month-old infants discriminate approximants and vowels when the spectral shape is modified to emphasize high- or low-frequency information. Infants were presented with /r/-/l/ and /ɔ/-/ɐ/ in three conditions: (a) unmodified; (b) -6 dB/octave tilt; and (c) +6 dB/octave tilt. Six-month-olds discriminated /ɔ/-/ɐ/ in conditions (a) and (b), and /r/-/l/ in conditions (a) and (c), but 9-month-olds only discriminated when unmodified. The results reflect native-language attunement. Six-month-olds discriminate spectrally modified sounds that emphasize relevant cues, but by 9 months, infants are sensitive to the native spectral profiles of speech.

The development of infants’ sensitivity to modified spectral tilt: Fricatives, approximants, and vowels.

In early infancy, speech perception is based on innate psychoacoustic thresholds allowing young infants to discriminate a wide range of speech contrasts. However, as infants accumulate knowledge of their native language, they begin attuning to native speech sounds: first vowels around 6 months; then consonants around 9–12 months. Now that hearing‐impaired infants are being diagnosed and fitted with hearing aids early in life, there is a need to investigate how speech is amplified in infant hearing aids. This study examined whether infants would benefit from positive, negative, or unmodified spectral tilt. Spectral tilts of +6dB/octave and −6dB/octave (as found in hearing aids) were applied to three speech contrasts (fricatives, approximants, vowels) and in a third condition the contrasts remained unmodified. Normal‐hearing 6‐ and 9‐month‐olds were tested using an habituation procedure to determine whether positive, negative, or unmodified tilt aids discrimination of the speech contrasts. The results showe...

Perceptual attunement in infants at risk of reading disabilities.

Impaired phonological processing has been found to have a reciprocal casual association with the reading ability of people with reading difficult‐ies. Further, there is growing evidence that problems in phonological processing are present at birth as research shows that infants with a family history of these disorders have atypical neural electrical responses (ERPs) to speech stimuli. However, the nature of the phonological deficit is not clear. This study examined the phonological development of at‐risk 9‐ to 12‐month‐old infants (n=18) and a control group (n=18). Their discrimination performance was evaluated using the habituation‐dishabituation task to test their ability to discriminate the confusable native contrast, /fa‐tha/ and the non‐native contrast, /k’i‐q’i/ from Werker and Tees (1984). In line with core phonological deficit hypothesis and hereditary accounts of reading difficulties, infants’ attunement to their native language was significantly correlated with parental phonological ability meas...