Variability in Quantity and Quality of Early Linguistic Experience in Children With Cochlear Implants: Evidence from Analysis of Natural Auditory Environments.

OBJECTIVES: Understanding how quantity and quality of language input vary across children with cochlear implants (CIs) is important for explaining sources of large individual differences in language outcomes of this at-risk pediatric population. Studies have mostly focused either on intervention-related, device-related, and/or patient-related factors, or relied on data from parental reports and laboratory-based speech corpus to unravel factors explaining individual differences in language outcomes among children with CIs. However, little is known about the extent to which children with CIs differ in quantity and quality of language input they experience in their natural linguistic environments. To address this knowledge gap, the present study analyzed the quantity and quality of language input to early-implanted children (age of implantation <23 mo) during the first year after implantation. DESIGN: Day-long Language ENvironment Analysis (LENA) recordings, derived from home environments of 14 early-implanted children, were analyzed to estimate numbers of words per day, type-token ratio (TTR), and mean length of utterance in morphemes (MLUm) in adults' speech. Properties of language input were analyzed across these three dimensions to examine how input in home environments varied across children with CIs in quantity, defined as number of words, and quality, defined as whether speech was child-directed or overheard. RESULTS: Our per-day estimates demonstrated that children with CIs were highly variable in the number of total words (mean ± SD = 25,134 ± 9,267 words) and high-quality child-directed words (mean ± SD = 10,817 ± 7,187 words) they experienced in a day in their home environments during the first year after implantation. The results also showed that the patterns of variability across children in quantity and quality of language input changes depending on whether the speech was child-directed or overheard. Children also experienced highly different environments in terms of lexical diversity (as measured by TTR) and morphosyntactic complexity (as measured by MLUm) of language input. The results demonstrated that children with CIs varied substantially in the quantity and quality of language input experienced in their home environments. More importantly, individual children experienced highly variable amounts of high-quality, child-directed speech, which may drive variability in language outcomes across children with CIs. CONCLUSIONS: Analyzing early language input in natural, linguistic environments of children with CIs showed that the quantity and quality of early linguistic input vary substantially across individual children with CIs. This substantial individual variability suggests that the quantity and quality of early linguistic input are potential sources of individual differences in outcomes of children with CIs and warrant further investigation to determine the effects of this variability on outcomes.

The Role of Secondary-Stressed and Unstressed-Unreduced Syllables in Word Recognition: Acoustic and Perceptual Studies with Russian Learners of English.

The importance of secondary-stressed (SS) and unstressed-unreduced (UU) syllable accuracy for spoken word recognition in English is as yet unclear. An acoustic study first investigated Russian learners' of English production of SS and UU syllables. Significant vowel quality and duration reductions in Russian-spoken SS and UU vowels were found, likely due to a transfer of native phonological features. Next, a cross-modal phonological priming technique combined with a lexical decision task assessed the effect of inaccurate SS and UU syllable productions on native American English listeners' speech processing. Inaccurate UU vowels led to significant inhibition of lexical access, while reduced SS vowels revealed less interference. The results have implications for understanding the role of SS and UU syllables for word recognition and English pronunciation instruction.

Long-term temporal tracking of speech rate affects spoken-word recognition.

Humans unconsciously track a wide array of distributional characteristics in their sensory environment. Recent research in spoken-language processing has demonstrated that the speech rate surrounding a target region within an utterance influences which words, and how many words, listeners hear later in that utterance. On the basis of hypotheses that listeners track timing information in speech over long timescales, we investigated the possibility that the perception of words is sensitive to speech rate over such a timescale (e.g., an extended conversation). Results demonstrated that listeners tracked variation in the overall pace of speech over an extended duration (analogous to that of a conversation that listeners might have outside the lab) and that this global speech rate influenced which words listeners reported hearing. The effects of speech rate became stronger over time. Our findings are consistent with the hypothesis that neural entrainment by speech occurs on multiple timescales, some lasting more than an hour.

Phonetic variation in consonants in infant-directed and adult-directed speech: the case of regressive place assimilation in word-final alveolar stops.

Pronunciation variation is under-studied in infant-directed speech, particularly for consonants. Regressive place assimilation involves a word-final alveolar stop taking the place of articulation of a following word-initial consonant. We investigated pronunciation variation in word-final alveolar stop consonants in storybooks read by forty-eight mothers in adult-directed or infant-directed style to infants aged approximately 0;3, 0;9, 1;1, or 1;8. We focused on phonological environments where regressive place assimilation could occur, i.e., when the stop preceded a word-initial labial or velar consonant. Spectrogram, waveform, and perceptual evidence was used to classify tokens into four pronunciation categories: canonical, assimilated, glottalized, or deleted. Results showed a reliable tendency for canonical variants to occur in infant-directed speech more often than in adult-directed speech. However, the otherwise very similar distributions of variants across addressee and age group suggested that infants largely experience statistical distributions of non-canonical consonantal pronunciation variants that mirror those experienced by adults.

Auditory rhythm discrimination in adults who stutter: An fMRI study.

Rhythm perception deficits have been linked to neurodevelopmental disorders affecting speech and language. Children who stutter have shown poorer rhythm discrimination and attenuated functional connectivity in rhythm-related brain areas, which may negatively impact timing control required for speech. It is unclear whether adults who stutter (AWS), who are likely to have acquired compensatory adaptations in response to rhythm processing/timing deficits, are similarly affected. We compared rhythm discrimination in AWS and controls (total n = 36) during fMRI in two matched conditions: simple rhythms that consistently reinforced a periodic beat, and complex rhythms that did not (requiring greater reliance on internal timing). Consistent with an internal beat deficit hypothesis, behavioral results showed poorer complex rhythm discrimination for AWS than controls. In AWS, greater stuttering severity was associated with poorer rhythm discrimination. AWS showed increased activity within beat-based timing regions and increased functional connectivity between putamen and cerebellum (supporting interval-based timing) for simple rhythms.

Effects of deafness on acoustic characteristics of American English tense/lax vowels in maternal speech to infants.

Recent studies have demonstrated that mothers exaggerate phonetic properties of infant-directed (ID) speech. However, these studies focused on a single acoustic dimension (frequency), whereas speech sounds are composed of multiple acoustic cues. Moreover, little is known about how mothers adjust phonetic properties of speech to children with hearing loss. This study examined mothers' production of frequency and duration cues to the American English tense/lax vowel contrast in speech to profoundly deaf (N = 14) and normal-hearing (N = 14) infants, and to an adult experimenter. First and second formant frequencies and vowel duration of tense (/i/, /u/) and lax (/I/, /ʊ/) vowels were measured. Results demonstrated that for both infant groups mothers hyperarticulated the acoustic vowel space and increased vowel duration in ID speech relative to adult-directed speech. Mean F2 values were decreased for the /u/ vowel and increased for the /I/ vowel, and vowel duration was longer for the /i/, /u/, and /I/ vowels in ID speech. However, neither acoustic cue differed in speech to hearing-impaired or normal-hearing infants. These results suggest that both formant frequencies and vowel duration that differentiate American English tense/lx vowel contrasts are modified in ID speech regardless of the hearing status of the addressee.

Altering context speech rate can cause words to appear or disappear.

Speech is produced over time, and this makes sensitivity to timing between speech events crucial for understanding language. Two experiments investigated whether perception of function words (e.g., or, are) is rate dependent in casual speech, which often contains phonetic segments that are spectrally quite reduced. In Experiment 1, talkers spoke sentences containing a target function word; slowing talkers' speech rate around this word caused listeners to perceive sentences as lacking the word (e.g., leisure or time was perceived as leisure time). In Experiment 2, talkers spoke matched sentences lacking a function word; speeding talkers' speech rate around the region in which the function word had been embedded in Experiment 1 caused listeners to perceive a function word that was never spoken (e.g., leisure time was perceived as leisure or time). The results suggest that listeners formed expectancies based on speech rate, and these expectancies influenced the number of words and word boundaries perceived. These findings may help explain the robustness of speech recognition when speech signals are distorted (e.g., because of a casual speaking style).

Pitch range variation in English tonal contrasts: continuous or categorical?

The importance of pitch range variation for intonational meaning and theory is well known; however, whether pitch range is a phonetic dimension which is treated categorically in English remains unclear. To test this possibility, three intonation continua varying in pitch range were constructed which had endpoints with contrastive representations under autosegmental-metrical (AM) theory: H* vs. L+H*, H* with 'peak delay' vs. L*+H, and %H L* vs. L*. The prediction derived from AM theory was that the reproduction of continuous pitch range variation should show a discrete pattern reflecting a change in the phonological representation of tonal sequences and in the number of tonal targets across each continuum. Participants' reproductions of each stimulus set showed continuous variation in pitch range, suggesting that pitch range is a gradient phonetic dimension in English conveying semantic contrast, similar to the formant space for vowels. Moreover, the gradience observed in productions across all parts of the pitch range suggests that contours within each series had the same number of tonal targets. The results support a version of AM theory in which rises and falls are usually comprised of two tonal targets, with strictly monotonic f(0) interpolation between them.

Not just a function of function words: Distal speech rate influences perception of prosodically weak syllables.

Listeners resolve ambiguities in speech perception using multiple sources, including non-local or distal speech rate (i.e., the speech rate of material surrounding a particular region). The ability to resolve ambiguities is particularly important for the perception of casual, everyday productions, which are often produced using phonetically reduced forms. Here, we examine whether the distal speech rate effect is specific to a lexical class of words and/or to particular lexical or phonological contexts. In Experiment 1, we examined whether distal speech rate influenced perception of phonologically similar content words differing in number of syllables (e.g., form/forum). In Experiment 2, we used both transcription and word-monitoring tasks to examine whether distal speech rate influenced perception of a reduced vowel, causing lexical reorganization (e.g., cease, see us). Distal speech rate influenced perception of lexical content in both experiments. This demonstrates that distal rate influences perception of a lexical class other than function words and affects perception in a variety of phonological and lexical contexts. These results support a view that distal speech rate is a pervasive source of information with far-reaching consequences for perception of lexical content and word segmentation.

A study of regressive place assimilation in spontaneous speech and its implications for spoken word recognition.

Regressive place assimilation is a form of pronunciation variation in which a word-final alveolar sound takes the place of articulation of a following labial or velar sound, as when green boat is pronounced greem boat. How listeners recover the intended word (e.g., green, given greem) has been a major focus of spoken word recognition theories. However, the extent to which this variation occurs in casual, unscripted speech has previously not been reported. Two studies of pronunciation variation were conducted using a spontaneous speech corpus. First, phonetic labeling data were used to identify contexts in which assimilation could occur, namely, when a word-final alveolar stop (/t/, /d/, or /n/) was followed by a velar or labial consonant. Assimilation was indicated relatively infrequently, while deletion, glottalization, or canonical pronunciations were more often indicated. Moreover, lexical frequency was shown to affect pronunciation; high frequency lexical items showed more types of variation. Second, acoustic analyses showed that neither place of articulation cues (indicated by second formant variation) nor relative amplitude was sufficient to distinguish assimilated from deleted and canonical variants; only when closure duration was additionally taken into account were these three variant types distinguishable. Implications for theories of word recognition are discussed.

Rate dependent speech processing can be speech specific: Evidence from the perceptual disappearance of words under changes in context speech rate.

The perception of reduced syllables, including function words, produced in casual speech can be made to disappear by slowing the rate at which surrounding words are spoken (Dilley & Pitt, Psychological Science, 21(11), 1664-1670. doi: 10.1177/0956797610384743 , 2010). The current study explored the domain generality of this speech-rate effect, asking whether it is induced by temporal information found only in speech. Stimuli were short word sequences (e.g., minor or child) appended to precursors that were clear speech, degraded speech (low-pass filtered or sinewave), or tone sequences, presented at a spoken rate and a slowed rate. Across three experiments, only precursors heard as intelligible speech generated a speech-rate effect (fewer reports of function words with a slowed context), suggesting that rate-dependent speech processing can be domain specific.

Revisiting Neil Armstrongs Moon-Landing Quote: Implications for Speech Perception, Function Word Reduction, and Acoustic Ambiguity.

Neil Armstrong insisted that his quote upon landing on the moon was misheard, and that he had said one small step for a man, instead of one small step for man. What he said is unclear in part because function words like a can be reduced and spectrally indistinguishable from the preceding context. Therefore, their presence can be ambiguous, and they may disappear perceptually depending on the rate of surrounding speech. Two experiments are presented examining production and perception of reduced tokens of for and for a in spontaneous speech. Experiment 1 investigates the distributions of several acoustic features of for and for a. The results suggest that the distributions of for and for a overlap substantially, both in terms of temporal and spectral characteristics. Experiment 2 examines perception of these same tokens when the context speaking rate differs. The perceptibility of the function word a varies as a function of this context speaking rate. These results demonstrate that substantial ambiguity exists in the original quote from Armstrong, and that this ambiguity may be understood through context speaking rate.

English-learning infants' segmentation of verbs from fluent speech.

Two experiments sought to extend the demonstration of English-learning infants' abilities to segment nouns from fluent speech to a new lexical class: verbs. Moreover, we explored whether two factors previously shown to influence noun segmentation, stress pattern (strong-weak or weak-strong) and type of initial phoneme (consonant or vowel), also influence verb segmentation. Our results establish the early emergence of verb segmentation in English: by 13.5 months for strong-weak consonant- or vowel-initial verbs and for weak-strong consonant-initial verbs; and by 16.5 months for weak-strong verbs beginning with a vowel. This generalizes previous reports of early segmentation to a new lexical class, thereby providing additional evidence that segmentation is likely to contribute to lexical acquisition. The effects of stress pattern and onset type found are similar to those previously obtained for nouns, in that verbs with a weak-strong stress pattern and verbs beginning with a vowel appear to be at a disadvantage in segmentation. Finally, we present prosodic analyses that suggest a possible effect of prosodic boundary and pitch accent distribution on segmentation. These prosodic differences potentially explain a developmental lag in verb segmentation observed in the present study compared to earlier findings for noun segmentation.

Metrical expectations from preceding prosody influence perception of lexical stress.

Two visual-world experiments tested the hypothesis that expectations based on preceding prosody influence the perception of suprasegmental cues to lexical stress. The results demonstrate that listeners' consideration of competing alternatives with different stress patterns (e.g., 'jury/gi'raffe) can be influenced by the fundamental frequency and syllable timing patterns across material preceding a target word. When preceding stressed syllables distal to the target word shared pitch and timing characteristics with the first syllable of the target word, pictures of alternatives with primary lexical stress on the first syllable (e.g., jury) initially attracted more looks than alternatives with unstressed initial syllables (e.g., giraffe). This effect was modulated when preceding unstressed syllables had pitch and timing characteristics similar to the initial syllable of the target word, with more looks to alternatives with unstressed initial syllables (e.g., giraffe) than to those with stressed initial syllables (e.g., jury). These findings suggest that expectations about the acoustic realization of upcoming speech include information about metrical organization and lexical stress and that these expectations constrain the initial interpretation of suprasegmental stress cues. These distal prosody effects implicate online probabilistic inferences about the sources of acoustic-phonetic variation during spoken-word recognition.

Age-Related Differences in Speech Rate Perception Do Not Necessarily Entail Age-Related Differences in Speech Rate Use.

PURPOSE: A new literature has suggested that speech rate can influence the parsing of words quite strongly in speech. The purpose of this study was to investigate differences between younger adults and older adults in the use of context speech rate in word segmentation, given that older adults perceive timing information differently from younger ones. METHOD: Younger (18-25 years) and older (55-65 years) adults performed a sentence transcription task for sentences that varied in speech rate context (i.e., distal speech rate) and a syntactic cue to the presence of a word boundary. RESULTS: There were no differences between younger and older adults in their use of the distal speech rate cue to word segmentation. CONCLUSIONS: The differences previously documented between younger and older adults in their perception of speech rate cues do not necessarily translate to older adults' use of those cues. Older adults' difficulties with compressed speech may arise from problems broader than just speech rate alone.

Vowel space characteristics of speech directed to children with and without hearing loss.

PURPOSE: This study examined vowel characteristics in adult-directed (AD) and infant-directed (ID) speech to children with hearing impairment who received cochlear implants or hearing aids compared with speech to children with normal hearing. METHOD: Mothers' AD and ID speech to children with cochlear implants (Study 1, n=20) or hearing aids (Study 2, n=11) was compared with mothers' speech to controls matched on age and hearing experience. The first and second formants of vowels /i/, /ɑ/, and /u/ were measured, and vowel space area and dispersion were calculated. RESULTS: In both studies, vowel space was modified in ID compared with AD speech to children with and without hearing loss. Study 1 showed larger vowel space area and dispersion in ID compared with AD speech regardless of infant hearing status. The pattern of effects of ID and AD speech on vowel space characteristics in Study 2 was similar to that in Study 1, but depended partly on children's hearing status. CONCLUSION: Given previously demonstrated associations between expanded vowel space in ID compared with AD speech and enhanced speech perception skills, this research supports a focus on vowel pronunciation in developing intervention strategies for improving speech-language skills in children with hearing impairment.

Individual differences in the perception of melodic contours and pitch-accent timing in speech: Support for domain-generality of pitch processing.

Do the same mechanisms underlie processing of music and language? Recent investigations of this question have yielded inconsistent results. Likely factors contributing to discrepant findings are use of small samples and failure to control for individual differences in cognitive ability. We investigated the relationship between music and speech prosody processing, while controlling for cognitive ability. Participants (n = 179) completed a battery of cognitive ability tests, the Montreal Battery of Evaluation of Amusia (MBEA) to assess music perception, and a prosody test of pitch peak timing discrimination (early, as in insight vs. late, incite). Structural equation modeling revealed that only music perception was a significant predictor of prosody test performance. Music perception accounted for 34.5% of variance on prosody test performance; cognitive abilities and music training added only about 8%. These results indicate musical pitch and temporal processing are highly predictive of pitch discrimination in speech processing, even after controlling for other possible predictors of this aspect of language processing.

Evidence for a rhythm perception deficit in children who stutter.

Stuttering is a neurodevelopmental disorder that affects the timing and rhythmic flow of speech production. When speech is synchronized with an external rhythmic pacing signal (e.g., a metronome), even severe stuttering can be markedly alleviated, suggesting that people who stutter may have difficulty generating an internal rhythm to pace their speech. To investigate this possibility, children who stutter and typically-developing children (n=17 per group, aged 6-11 years) were compared in terms of their auditory rhythm discrimination abilities of simple and complex rhythms. Children who stutter showed worse rhythm discrimination than typically-developing children. These findings provide the first evidence of impaired rhythm perception in children who stutter, supporting the conclusion that developmental stuttering may be associated with a deficit in rhythm processing.

Phonetic modification of vowel space in storybook speech to infants up to 2 years of age.

PURPOSE: A large body of literature has indicated vowel space area expansion in infant-directed (ID) speech compared with adult-directed (AD) speech, which may promote language acquisition. The current study tested whether this expansion occurs in storybook speech read to infants at various points during their first 2 years of life. METHOD: In 2 studies, mothers read a storybook containing target vowels in ID and AD speech conditions. Study 1 was longitudinal, with 11 mothers recorded when their infants were 3, 6, and 9 months old. Study 2 was cross-sectional, with 48 mothers recorded when their infants were 3, 9, 13, or 20 months old (n=12 per group). The 1st and 2nd formants of vowels /i/, /ɑ/, and /u/ were measured, and vowel space area and dispersion were calculated. RESULTS: Across both studies, 1st and/or 2nd formant frequencies shifted systematically for /i/ and /u/ vowels in ID compared with AD speech. No difference in vowel space area or dispersion was found. CONCLUSIONS: The results suggest that a variety of communication and situational factors may affect phonetic modifications in ID speech, but that vowel space characteristics in speech to infants stay consistent across the first 2 years of life.

Distal prosody affects learning of novel words in an artificial language.

The distal prosodic patterning established at the beginning of an utterance has been shown to influence downstream word segmentation and lexical access. In this study, we investigated whether distal prosody also affects word learning in a novel (artificial) language. Listeners were exposed to syllable sequences in which the embedded words were either congruent or incongruent with the distal prosody of a carrier phrase. Local segmentation cues, including the transitional probabilities between syllables, were held constant. During a test phase, listeners rated the items as either words or nonwords. Consistent with the perceptual grouping of syllables being predicted by distal prosody, congruent items were more likely to be judged as words than were incongruent items. The results provide the first evidence that perceptual grouping affects word learning in an unknown language, demonstrating that distal prosodic effects may be independent of lexical or other language-specific knowledge.