Maternal education influences Australian infants' language experience from six months.

Disparities in children's early language skills associated with socioeconomic factors have led to many studies examining children's early language environments, but few as yet in the first year of life. This longitudinal study assessed the home language environments of 50 Australian infants, who varied in maternal education (university education, or not). Full-day audio recordings were collected and analyzed using the LENA system when infants were aged 6-9 months and 12-15 months. Using the device-specific analysis software, we assessed 12-h projected counts of (1) adult speech input, (2) conversational interactions, and (3) child vocalizations. At both ages, higher maternal education was associated with higher counts of adult words and conversational turns, but not child vocalizations. The study adds to the literature by demonstrating disparities in the infants' language experience within the first year of life, related to mothers' education, with implications for early intervention and parenting supports.

Newborns' sensitivity to the visual aspects of infant-directed speech: Evidence from point-line displays of talking faces.

The first time a newborn is held, he is attracted by the human's face. A talking face is even more captivating, as it is the first time he or she hears and sees another human talking. Older infants are relatively good at detecting the relationship between images and sounds when someone is addressing to them, but it is unclear whether this ability is dependent on experience or not. Using an intermodal matching procedure, we presented newborns with 2 silent point-line displays representing the same face uttering different sentences while they were hearing a vocal-only utterance that matched 1 of the 2 stimuli. Nearly all of the newborns looked longer at the matching point-line face than at the mismatching 1, with prior exposure to the stimuli (Experiment 1) or without (Experiment 2). These results are interpreted in terms of newborns' ability to extract common visual and auditory information of continuous speech events despite a short experience with talking faces. The implications are discussed in the light of the language processing and acquisition literature. (PsycINFO Database Record

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

This study's 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.

Affective Properties of Mothers' Speech to Infants With Hearing Impairment and Cochlear Implants.

PURPOSE: The affective properties of infant-directed speech influence the attention of infants with normal hearing to speech sounds. This study explored the affective quality of maternal speech to infants with hearing impairment (HI) during the 1st year after cochlear implantation as compared to speech to infants with normal hearing. METHOD: Mothers of infants with HI and mothers of infants with normal hearing matched by age (NH-AM) or hearing experience (NH-EM) were recorded playing with their infants during 3 sessions over a 12-month period. Speech samples of 25 s were low-pass filtered, leaving intonation but not speech information intact. Sixty adults rated the stimuli along 5 scales: positive/negative affect and intention to express affection, to encourage attention, to comfort/soothe, and to direct behavior. RESULTS: Low-pass filtered speech to HI and NH-EM groups was rated as more positive, affective, and comforting compared with the such speech to the NH-AM group. Speech to infants with HI and with NH-AM was rated as more directive than speech to the NH-EM group. Mothers decreased affective qualities in speech to all infants but increased directive qualities in speech to infants with NH-EM over time. CONCLUSIONS: Mothers fine-tune communicative intent in speech to their infant's developmental stage. They adjust affective qualities to infants' hearing experience rather than to chronological age but adjust directive qualities of speech to the chronological age of their infants.

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.

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.

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.

Development of phonological constancy: 19-month-olds, but not 15-month-olds, identify words in a non-native regional accent.

By 12 months, children grasp that a phonetic change to a word can change its identity (phonological distinctiveness). However, they must also grasp that some phonetic changes do not (phonological constancy). To test development of phonological constancy, sixteen 15-month-olds and sixteen 19-month-olds completed an eye-tracking task that tracked their gaze to named versus unnamed images for familiar words spoken in their native (Australian) and an unfamiliar non-native (Jamaican) regional accent of English. Both groups looked longer at named than unnamed images for Australian pronunciations, but only 19-month-olds did so for Jamaican pronunciations, indicating that phonological constancy emerges by 19 months. Vocabulary size predicted 15-month-olds' identifications for the Jamaican pronunciations, suggesting vocabulary growth is a viable predictor for phonological constancy development.

The development of language constancy: attention to native versus nonnative accents.

The time frame for infants' acquisition of language constancy was probed, using the phonetic variation in a rarely heard accent (South African English) or a frequently heard accent (American English). A total of 156 Australian infants were tested. Six-month-olds looked longer to Australian English than less commonly heard South African accent, but at 9 months, showed similar looking times. With the more frequently heard American accent, 3-month-olds looked longer to Australian and American English, whereas 6-month-olds looked equally. Together these results imply that in the 1st year, differential attention to native versus nonnative accents decreases as infants develop a sense of language constancy for the common native language. However, experience with the nonnative accent can expedite this process.

Mommy, speak clearly: induced hearing loss shapes vowel hyperarticulation.

Talkers hyperarticulate vowels when communicating with listeners that require increased speech intelligibility. Vowel hyperarticulation is said to be motivated by knowledge of the listener's linguistic needs because it typically occurs in speech to infants, foreigners and hearing-impaired listeners, but not to non-verbal pets. However, the degree to which vowel hyperarticulation is determined by feedback from the listener is surprisingly less well understood. This study examines whether mothers' speech input is driven by knowledge of the infant's linguistic competence, or by the infant's feedback cues. Specifically, we manipulated (i) mothers' knowledge of whether they believed their infants could hear them or not, and (ii) the audibility of the speech signal available to the infant (full or partial audibility, or inaudible). Remarkably, vowel hyperarticulation was completely unaffected by mothers' knowledge; instead, there was a reduction in the degree of hyperarticulation such that vowels were hyperarticulated to the greatest extent in the full audibility condition, there was reduced hyperarticulation in the partially audible condition, and no hyperarticulation in the inaudible condition. Thus, while it might be considered adaptive to hyperarticulate speech to the hearing-impaired adult or infant, when these two factors (infant and hearing difficulty) are coupled, vowel hyperarticulation is sacrificed. Our results imply that infant feedback drives talker behavior and raise implications for intervention strategies used with carers of hearing-impaired infants.

Modified spectral tilt affects older, but not younger, infants' native-language fricative discrimination.

PURPOSE: It is important to ensure that hearing aid fitting strategies for infants take into account the infant's developing speech perception system. As a way of exploring this issue, this study examined how 6- and 9-month-olds with normal hearing perceive native-language speech in which the natural spectral shape was altered to emphasize either high-frequency (positive spectral tilt) or low-frequency (negative spectral tilt) information. METHOD: Discrimination was tested using a visual habituation procedure. Forty-eight 6-month-olds and forty-eight 9-month-olds were presented with a fricative contrast, /f/-/s/, in 1 of 3 conditions: (a) as unmodified speech; (b) with a -6 dB/octave tilt; or (c) with a +6 dB/octave tilt. RESULTS: Six-month-olds showed evidence of discriminating /f/-/s/ in all 3 conditions, but 9-month-olds showed such evidence only in the unmodified condition. CONCLUSIONS: The findings suggest that the perceptual reorganization that emerges for consonants at the end of the first year affects 9-month-olds' discrimination of native speech sounds. Perceptual reorganization is usually indexed by a decline in the ability to discriminate nonnative speech sounds. In this study, 6-month-olds demonstrated an acoustic-based sensitivity to both modified and unmodified native speech sounds, but 9-month-olds were most sensitive to the unmodified speech sounds that adhered to the native spectral profile.

Maternal interactions with a hearing and hearing-impaired twin: similarities and differences in speech input, interaction quality, and word production.

PURPOSE: This study examined a mother's speech style and interactive behaviors with her twin sons: 1 with bilateral hearing impairment (HI) and the other with normal hearing (NH). METHOD: The mother was video-recorded interacting with her twin sons when the boys were 12.5 and 22 months of age. Mean F0, F0 range, duration, and F1/F2 vowel space of the corner vowels /i/, /u/, and /a/ were compared in her infant-directed (ID) and adult-directed (AD) speech. The interactions were also coded for emotional availability, and vocabulary size was collected at 17 and 22 months. RESULTS: Acoustic analyses revealed no difference among mean F0, F0 range, and duration between the twins. In contrast, when the corner vowels were plotted in F1/F2 vowel space, the results showed a diminished vowel space in speech to the HI twin compared to the NH twin. Ratings of emotional availability were lower for the HI than the NH twin, but the HI twin had a larger expressive vocabulary on both occasions, albeit in the lower percentile. CONCLUSIONS: The mother appears more focused on maintaining the attention of the HI infant using the typical ID exaggerations to prosody and overlooking linguistic features such as the hyperarticulation of her vowels. The results have implications for early intervention strategies.

The shift in infant preferences for vowel duration and pitch contour between 6 and 10 months of age.

This study investigates the influence of the acoustic properties of vowels on 6- and 10-month-old infants' speech preferences. The shape of the contour (bell or monotonic) and the duration (normal or stretched) of vowels were manipulated in words containing the vowels /i/ and /u/, and presented to infants using a two-choice preference procedure. Experiment 1 examined contour shape: infants heard either normal-duration bell-shaped and monotonic contours, or the same two contours with stretched duration. The results show that 6-month-olds preferred bell to monotonic contours, whereas 10-month-olds preferred monotonic to bell contours. In Experiment 2, infants heard either normal-duration and stretched bell contours, or normal-duration and stretched monotonic contours. As in Experiment 1, infants showed age-specific preferences, with 6-month-olds preferring stretched vowels, and 10-month-olds preferring normal-duration vowels. Infants' attention to the acoustic qualities of vowels, and to speech in general, undergoes a dramatic transformation in the final months of the first year, a transformation that aligns with the emergence of other developmental milestones in speech perception.

Age-Specific Preferences for Infant-Directed Affective Intent.

This study examined the developmental course of infants' attentional preferences for 3 types of infant-directed affective intent, which have been shown to be commonly used at particular ages in the first year of life. Specifically, Kitamura and Burnham (2003) found mothers' tone of voice in infant-directed speech is most comforting between birth and 3 months, most approving at 6 months, and most directive at 9 months. Thus, the aim of this study was to assess whether there is a relation between the type of affective intent used by mothers at each age point, and infants' affective intent preferences. Each infant group, 3-, 6-, and 9-month-olds, was played the 3 types of affective intent alternating across a single test session. When analyzed across age, the interactions revealed the predicted developmental trajectory; that is, infant preferences transformed between 3 and 6 months from comforting to approving, and between 6 and 9 months, from approving to directive. However, when analyzed separately by age, it was shown that 3-month-olds preferred comforting to other types; 6-month-olds preferred approving to directive, but listened equally to approving and comforting; and 9-month-olds showed no preference for any type of affective intent. Because it was possible that 9-month-olds were more focused on phonetic and phonotactic information, a new group of 9-month-olds was tested with intonation-only versions of the 3 affective intent types. Under these conditions, they were found to prefer directive to comforting, but not directive to approving types. The results of this study have implications for what infants pay attention to in their social and linguistic environment over the course of the first year.