Biomedical subjects

S Nittrouer

Publications and source records attributed to S Nittrouer.

At least 19 recordsLinked to original sources

PubMed2000

The effect of segmental order on fricative labeling by children and adults.

We examined whether children modify their perceptual weighting strategies for speech on the basis of the order of segments within a syllable, as adults do. To this end, fricative-vowel (FV) and vowel-fricative (VF) syllables were constructed with synthetic noises from an/[symbol: see text]/-to-/s/continuum combined with natural/a/and/u/portions with transitions appropriate for a preceding or a following /[symbol: see text]/or/s/. Stimuli were played in their original order to adults and children (ages of 7 and 5 years) in Experiment 1 and in reversed order in Experiment 2. The results for adults and, to a lesser extent, those for 7-year-olds replicated earlier results showing that adults assign different perceptual weights to acoustic properties, depending on segmental order. In contrast, results for 5-year-olds suggested that these listeners applied the same strategies during fricative labeling, regardless of segmental order. Thus, the flexibility to modify perceptual weighting strategies for speech according to segmental order apparently emerges with experience.

Adult↗

PubMed1999

Do temporal processing deficits cause phonological processing problems?

This study tested the hypothesis that temporal processing deficits underlie phonological processing problems. The subjects were children aged 8 to 10 years (N = 110) who were separated into 2 groups on the basis of whether their reading scores were normal or poor. As predicted by many earlier studies, children with poor reading scores demonstrate poor abilities on tests of phonological awareness, as well as on 2 other language tasks that depend on phonological processing. Two specific tests of the temporal processing hypothesis were conducted. Children in both groups were tested (a) on their abilities to recall sequences of nonspeech tones presented at various rates and (b) on their abilities to make phonetic decisions using brief and transitional properties of the speech signal, especially formant transitions (the purported "trouble spot" in the speech signal for children with phonological processing problems). The children with poor phonological processing abilities showed no special difficulty recalling rapidly presented nonspeech stimuli, and, in their phonetic decisions, they were able to use brief and transitional signal properties, including formant transitions, at least as well as other children. Therefore, no evidence was found to support the hypothesis that temporal processing deficits cause phonological processing problems.

Awareness↗

PubMed1998

Examining the role of auditory sensitivity in the developmental weighting shift.

Studies comparing children's and adults' labeling of speech stimuli have repeatedly shown that children's phonological decisions are more strongly related to portions of the signal that involve rapid spectral change (i.e., formant transitions) and less related to other signal components than are adults' decisions. Such findings have led to a model termed the Developmental Weighting Shift, which suggests that children initially assign particularly strong weight to formant transitions to help delimit individual words in the continuous speech stream but gradually modify these strategies to be more like those of adults as they learn about word-internal structure. The goal of the current study was to test a reasonable alternative: that these apparent age-related differences in perceptual weighting strategies for speech are instead due to age-related differences in auditory sensitivity. To this end, difference limens (DLs) were obtained from children (ages 5 and 7 years) and adults for three types of acoustic properties: dynamic-spectral, static-spectral, and temporal. Two testable hypotheses were offered: Labeling results could reflect either absolute differences in sensitivity between children and adults or relative differences in sensitivity within each group. Empirical support for either hypothesis would indicate that apparent developmental changes in perceptual weighting strategies are actually due to developmental changes in auditory sensitivity to acoustic properties. Results of this study contradicted predictions of both hypotheses, sustaining the suggestion that children's perceptual weighting strategies for speech-relevant acoustic properties change as they gain experience with a native language.

Age Factors↗

PubMed1998

The relative weighting of acoustic properties in the perception of [s] + stop clusters by children and adults.

We examined the perceptual weighting by children and adults of the acoustic properties specifying complete closure of the vocal tract following a syllable-initial [s]. Experiment 1 was a novel manipulation of previously examined acoustic properties (duration of a silent gap and first formant transition) and showed that children weight the first formant transition more than adults. Experiment 2, an acoustic analysis of naturally produced say and stay, revealed that, contrary to expectations, a burst can be present in stay and that first formant transitions do not necessarily distinguish say and stay in natural tokens. Experiment 3 manipulated natural speech portions to create stimuli that varied primarily in the duration of the silent gap and in the presence or absence of a stop burst, and showed that children weight these stop bursts less than adults. Taken together, the perception experiments support claims that children integrate multiple acoustic properties as adults do, but that they weight dynamic properties of the signal more than adults and weight static properties less.

Adult↗

PubMed1997

Predicting developmental shifts in perceptual weighting schemes.

Recent models of developmental changes in speech perception suggest that the weights assigned to acoustic properties change as children gain experience with a native language. Empirical evidence supports this position, but few suggestions have been offered as to what guides this shift. These three experiments were designed to improve our ability to predict how perceptual weighting schemes change with development. The specific hypothesis explored was twofold: (1) the weight assigned by adults to any one acoustic property differs across phonetic environments according to how informative that property is in each environment; and (2) the weight assigned by children to any one acoustic property differs less across phonetic environments because children have not fully learned the patterns of covariation between phonetic informativeness and environment for each property. Experiment 1 replicated previous findings of age-related differences in the weights assigned to noise spectra and formant transitions in labeling of syllable-initial fricatives (/s/ or /[symbol: see text]/). In experiment 2 the variation in F3-onset frequency associated with place of fricative constriction was eliminated. This property differs more (i.e., is more informative) in /u/ than in /a/. Accordingly adults' transition effect was reduced more for /u/ than for /a/ from experiment 1. Children's transition effect was similarly reduced across vowel environments. In experiment 3, F3-onset frequency was appropriately manipulated for both vowels, and adults transition effect increased more for /u/ than for /a/ from experiment 2. The increase in children's transition effect was more similar across vowels. We conclude that the children had not fully learned how information provided by F3 transitions varies across /a/ and /u/ environments, and suggest that developmental weighting shifts may be guided by children learning the relation between phonetic informativeness and environment.

Adult↗

PubMed1997

Developmental weighting shifts for noise components of fricative-vowel syllables.

Previous studies have convincingly shown that the weight assigned to vocalic formant transitions in decisions of fricative identity for fricative-vowel syllables decreases with development. Although these same studies suggested a developmental increase in the weight assigned to the noise spectrum, the role of the aperiodic-noise portions of the signals in these fricative decisions have not been as well-studied. The purpose of these experiments was to examine more closely developmental shifts in the weight assigned to the aperiodic-noise components of the signals in decisions of syllable-initial fricative identity. Two experiments used noises varying along continua from a clear /s/ percept to a clear /[symbol: see text]/ percept. In experiment 1, these noises were created by combining /s/ and /[symbol: see text]/ noises produced by a human vocal tract at different amplitude ratios, a process that resulted in stimuli differing primarily in the amplitude of a relatively low-frequency (roughly 2.2-kHz) peak. In experiment 2, noises that varied only in the amplitude of a similar low-frequency peak were created with a software synthesizer. Both experiments used synthetic /a/ and /u/ portions, and efforts were made to minimize possible contributions of vocalic formant transitions to fricative labeling. Children and adults labeled the resulting stimuli as /s/ vowel or /[symbol: see text]/ vowel. Combined results of the two experiments showed that children's responses were less influenced than those of adults by the amplitude of the low-frequency peak of fricative noises.

Adult↗

PubMed1996

Discriminability and perceptual weighting of some acoustic cues to speech perception by 3-year-olds.

Studies of children's speech perception have shown that young children process speech signals differently than adults. Specifically, the relative contributions made by various acoustic parameters to some linguistic decisions seem to differ for children and adults. Such findings have led to the hypothesis that there is a developmental shift in the perceptual weighting of acoustic parameters that results from experience with a native language (i.e., the Developmental Weighting Shift). This developmental shift eventually leads the child to adopt the optimal perceptual weighting strategy for the native language being learned (i.e., one that allows the listener to make accurate decisions about the phonemic structure or his or her native language). Although this proposal has intuitive appeal, there is at least one serious challenge that can be leveled against it: Perhaps age-related differences in speech perception can appropriately be explained by age-related differences in basic auditory-processing abilities. That is, perhaps children are not as sensitive as adults to subtle differences in acoustic structure and so make linguistic decisions based on the acoustic information that is most perceptually salient. The present study tested this hypothesis for the acoustic cues relevant to fricative identity in fricative-vowel syllables. Results indicated that 3-year-olds were not as sensitive to changes in these acoustic cues as adults are, but that these age-related differences in auditory sensitivity could not entirely account for age-related differences in perceptual weighting strategies.

Adult↗

PubMed1996

How children learn to organize their speech gestures: further evidence from fricative-vowel syllables.

Previous studies with fricative-vowel (FV) syllables have shown that the difference in overall spectrum between fricatives is less in children's speech than in that of adults, but that fricative noises show greater differences in the region of the second formant (F2) as a function of the upcoming vowel than those of adults at corresponding points in the fricative. These results have been interpreted as evidence that children produce fricatives that are not spatially differentiated as those of adults and that children initiate vowel gestures earlier during syllable production than adults do (Nittrouer, Studdert-Kennedy, & McGowan, 1989). The goals of the present study were (a) to replicate the previous age-related difference for F2 with FV syllables; (b) to test the alternative interpretation that age-related differences in fricative f2 reflect age-related differences in vocal-tract geometry; (c) to determine whether age-related differences in F2 (and so, by inference, in articulatory organization) might extend beyond the syllable boundaries, perhaps into the schwa of a preceding unstressed syllable; and (d) determine if gestures other than fricative gestures show less spatial differentiation in children's than in adults' speech. To these ends, F2 frequencies were measured in schwa-fricative-vowel utterances (consisting of the fricatives /s/ and [symbol:see text] and of the vowels /i/ and /a/) from 40 speakers (10 each of the ages of 3, 5, 7 years, and adults) at three locations (for the entire schwa, for 10 ms of fricative noise centered at 30 ms before voicing onset, and 10 pitch periods from vocalic center). Results of several analyses supported four conclusions: (a) the earlier finding was replicated; (b) age-related differences in vocal-tract geometry could not explain the age-related difference in vowel effects on fricative noise; (c) children master intersyllabic gestural organization prior to intrasyllabic gestural organization; and (d) unlike fricative gestures, children's vowel gestures are more spatially distinct than those of adults.

Adult↗

PubMed1996

The relation between speech perception and phonemic awareness: evidence from low-SES children and children with chronic OM.

The Developmental Weighting Shift (DWS) suggests that children adjust the weights they assign to the acoustic parameters of the speech signal as they gain experience with a native language, and that this developmental shift in perceptual weighting strategies is related to another developmental change: increased sensitivity to the phonetic structure of the speech signal. To test these claims, children presumed to differ in the amount of linguistic experience they had received during their preschool years participated in two kinds of tasks: a labeling task designed to estimate differences among groups in the weights assigned to various acoustic parameters, and tasks of phonemic awareness. The experimental groups were children from low-socioeconomic (low-SES) backgrounds, children with histories of chronic otitis media (OM), and children who experienced both conditions. A control group of children who experienced neither of these conditions also participated. The hypotheses were that, because of their diminished linguistic experience, children in the three experimental groups would display both more immature weighting strategies and poorer phonemic awareness than children in the control group, and that developmental advance in perceptual weighting strategies and phonemic awareness would be correlated. Results indicated that children with histories of chronic OM performed more poorly on both kinds of tasks than did children in the control group, and low-SES children performed more poorly still. Children experiencing both low-SES and chronic OM performed no differently than the low-SES children. These results provide support for the claim that the development of mature perceptual weighting strategies for speech and of phonemic awareness are related. Support is also provided for the claim that both depend on receiving sufficient and appropriate experience with a native language during the preschool years.

Child, Preschool↗

PubMed1995

"Say-stay" identification and psychoacoustic performance of hearing-impaired listeners.

Controversy exists over the extent to which psychoacoustic abilities explain speech perception. The present study addressed this issue by assessing the contribution of psychoacoustic abilities to speech identification by hearing-impaired listeners. Speech stimuli and nonspeech analogs were presented to normal-hearing and hearing-impaired listeners with varying degrees of hearing loss. Phonemic judgments for synthetic versions of "say-stay" stimuli were evaluated as a function of first formant onset frequency and of silence duration between the /s/ noise and the vocalic portion. Three psychoacoustic measures were obtained: glide onset frequency discrimination, gap detection in noise, and gap detection in speechlike composite signals. Although the resulting difference limens increased with increasing hearing loss, the acoustic cues to the speech contrast were available to all listeners. Nonetheless, the response patterns to the speech stimuli varied among groups in a manner that was not explained by the psychoacoustic results. Thus, although hearing-impaired listeners were able to detect and discriminate essential acoustic cues for speech, the perceptual organization of speech stimuli appeared to differ with degree of loss. Alternative explanations for the findings are considered, including the possible effect of hearing loss on auditory/linguistic experience.

Adolescent↗

PubMed1995

Children learn separate aspects of speech production at different rates: evidence from spectral moments.

One theoretical perspective on speech development holds that segmental structure gradually emerges in the utterances of children as their first words, realized as roughly specified patterns of gesture, are differentiated into patterns of precisely specified and carefully coordinated gestures. The purpose of the present study was to test one aspect of this theoretical position, namely that children's articulatory gestures are not as precisely specified as are those of adults. In addition, a related hypothesis was tested, namely that some patterns of gesture achieve adultlike precision sooner than others. To test these hypotheses, the first, third, and fourth spectral moments were derived for fricative (/s/ and /integral of) and for stop-burst (/t/ and /k/) noises in the speech samples of children (3 to 7 years of age) and of adults. First spectral moments for fricatives showed stronger consonant effects (i.e., /s/ vs /integral of/) for adults' than for children's samples. This acoustic finding replicated a previous result [Nittrouer et al, J. Speech Hear. Res. 32, 120-132 (1989)], and provided support for the hypothesis that some articulatory gestures are not as precisely specified in children's speech as in that of adults. First spectral moments for /t/ and /k/ revealed no age-related differences in the magnitude of the consonant effect, providing support for the hypothesis that some gestures achieve mature status sooner than others. Although not a focus of the present study, it was also found that children's /k/ first moments varied more than adults' as a function of vowel environment (/i/, /a/, or /u/). Thus further support was obtained for a finding described elsewhere: For at least some articulatory gestures, there is greater influence of one on another for children's than for adults' speech [e.g., Nittrouer et al., J. Speech Hear. Res. 32, 120-132 (1989); S. Nittrouer, J. Speech Hear. Res. 36, 959-971 (1993)].

Adult↗

PubMed1995

The perception of amplified speech by listeners with hearing loss: acoustic correlates.

Audibility-based approaches to hearing-aid selection generally have focused on the long-term average speech spectrum (LTASS). Advances in amplification technology (e.g., multiband signal processing, level-dependent frequency shaping, full dynamic range compression, adaptive compression) make it difficult to predict the audibility of short-term components of speech from the amplified LTASS. This study was designed to quantify the audibility of a specific phonemes as processed by two different hearing-aid circuits (linear and full dynamic range compression), and to investigate the relation between audibility and performance on a nonsense syllable recognition task. Data were obtained from three subjects with moderate sensorineural hearing loss. Nine unvoiced consonants were presented in two vowel contexts (/i/ and /a/) in both the pre- and post-vocalic position at three intensities. While the performance on selected conditions appeared to vary by hearing-aid type, only one subject showed a statistically significant difference between the two hearing-aid systems. Acoustic analyses revealed a variety of spectral and temporal changes to the speech signal following processing. Estimates of audibility were based upon each subject's thresholds and an acoustic analysis of the amplified signal that varied across phonemes and consonant position. A signal detection approach was used to predict performance from a simple measure of audibility.

Amplifiers, Electronic↗

PubMed1993

The emergence of mature gestural patterns is not uniform: evidence from an acoustic study.

Previous studies investigating the organization of articulatory gestures present conflicting accounts of age-related differences in the execution of the articulatory gestures themselves and in the organization of those gestures. Several methodological differences may help to explain these contradictions: First, different studies have used different measures, all of which reflect vocal-tract activity to varying extents; second, the articulatory gestures being analyzed differed across studies; third, the phonetic composition of syllables has varied; and finally, utterance length, and therefore complexity, has varied across studies. The purpose of this study was to investigate the possibility that the reason these methodological differences have led to contradictory results is because the emergence of mature gestural patterns in children's speech is not uniform. To accomplish this goal, detailed acoustic analyses were performed on schwa-stop-vowel utterances from adults and from children (3, 5, and 7 years of age). Temporal measures showed that some acoustic segments were longer in children's than in adults' samples, whereas others were similar in duration. Formant frequencies indicated that vocal-tract opening and closing achieve adult-like patterns of movement by the age of 3 years, but children's tongue gestures are constrained by phonetic context more than those of adults until at least the age of 7 years. Taken together, these results suggest that the pace of development for learning to produce and to coordinate articulatory gestures is not uniform. Thus, the contradictions in findings among earlier studies may very well reflect differences in choices of measurement and utterances to be analyzed, both of which may lead to evaluations of different aspects of gestural patterning.

Adult↗

PubMed1991

Phase relations of jaw and tongue tip movements in the production of VCV utterances.

A previous study by Nittrouer et al. [J. Acoust. Soc. Am. 84, 1653-1661 (1988)] found that the spatiotemporal relations between jaw and upper lip movements for speech were affected not only by the segmental structure of the utterance, but by stress pattern and rate of production, as well. Specifically, the angle on the vowel-to-vowel jaw cycle phase plane at which the upper lip began moving toward closure for an intervocalic consonant varied systematically and discretely with changes in vowel-cycle duration. The development of the X-ray microbeam has permitted the observation of these effects for gestures involving articulators other than the lips and jaw. In the present study, the onset of tongue tip movement for an intervocalic consonant was represented as an angle on the jaw cycle phase plane for vowel-consonant-vowel utterances. Although the tongue tip exhibited greater variability in its movement onset than the upper lip had, the relative phasing of tongue tip movement onset was also found to vary with jaw vowel-cycle duration: Any manipulation that shortened the jaw vowel cycle also served to reduce the phase angle at which the tongue tip began movement. This relation was not found to be continuous in nature, but rather a main effect of phonetic and nonphonetic factors.

Adult↗

PubMed1990

Acoustic measurements of men's and women's voices: a study of context effects and covariation.

Several acoustic measures of laryngeal activity were made on adult speech to help answer two questions left unresolved by previous work: (1) how each measure varies, if at all, with phonetic structure, and (2) what aspect of laryngeal activity each measure specifies. Speech samples of 15 syllables (three vowels in five prevocalic consonantal contexts) were collected from men and women at two times of the day (early morning and late afternoon). Eight measurements were made, mainly on slices extracted from the middle of the vocalic portions, and inferential and correlational statistics were applied to these measures. Results of the inferential tests indicated differences between men and women in how laryngeal adjustments are made, affecting relative amounts of vocal jitter and spectral tilt of the voicing source. In addition, the voicing and manner characteristics of the prevocalic consonant were found to affect fundamental frequency, cycle-to-cycle perturbations, and amount of aspiration noise. To a lesser extent, vowel height and front/back tongue placement also affected these acoustic source characteristics. Results of the correlational tests showed that different laryngeal mechanisms contributed differentially to signal-to-noise ratios for men and women, and these mechanisms were more greatly affected by fundamental frequency for men's samples. Finally, various acoustic measures of laryngeal noise were found to be related to the same underlying mechanism.

Adult↗

PubMed1990

Context effects in phoneme and word recognition by young children and older adults.

Perception is influenced both by characteristics of the stimulus, and by the context in which it is presented. The relative contributions of each of these factors depend, to some extent, on perceiver characteristics. The contributions of word and sentence context to the perception of phonemes within words and words within sentences, respectively, have been well studied for normal, young adults. However, far less is known about these context effects for much younger and older listeners. In the present study, measures of these context effects were obtained from young children (ages 4 years 6 months to 6 years 6 months) and from older adults (over 62 years), and compared with those of the young adults in an earlier study [A. Boothroyd and S. Nittrouer, J. Acoust. Soc. Am. 84, 101-114 (1988)]. Both children and older adults demonstrated poorer overall recognition scores than did young adults. However, responses of children and older adults demonstrated similar context effects, with two exceptions: Children used the semantic constraints of sentences to a lesser extent than did young or older adults, and older adults used lexical constraints to a greater extent than either of the other two groups.

Aged↗

PubMed1989

The perceptual effects of child-adult differences in fricative-vowel coarticulation.

Earlier work [Nittrouer et al., J. Speech Hear. Res. 32, 120-132 (1989)] demonstrated greater evidence of coarticulation in the fricative-vowel syllables of children than in those of adults when measured by anticipatory vowel effects on the resonant frequency of the fricative back cavity. In the present study, three experiments showed that this increased coarticulation led to improved vowel recognition from the fricative noise alone: Vowel identification by adult listeners was better overall for children's productions and was successful earlier in the fricative noise. This enhanced vowel recognition for children's samples was obtained in spite of the fact that children's and adults' samples were randomized together, therefore indicating that listeners were able to normalize the vowel information within a fricative noise where there often was acoustic evidence of only one formant associated primarily with the vowel. Correct vowel judgments were found to be largely independent of fricative identification. However, when another coarticulatory effect, the lowering of the main spectral prominence of the fricative noise for /u/ versus /i/, was taken into account, vowel judgments were found to interact with fricative identification. The results show that listeners are sensitive to the greater coarticulation in children's fricative-vowel syllables, and that, in some circumstances, they do not need to make a correct identification of the most prominently specified phone in order to make a correct identification of a coarticulated one.

Adult↗

PubMed1989

The emergence of phonetic segments: evidence from the spectral structure of fricative-vowel syllables spoken by children and adults.

A variety of evidence, including the speech errors of normal and aphasic speakers, and the metalinguistic skills of literate individuals, demonstrates that speech has an underlying phonemic organization. However, we know little about how this organization develops in the child. The purpose of the present study was to test the hypothesis that phoneme-sized phonetic segments emerge as functional units of perceptuomotor control from the child's gradual reorganization of the gestures forming its early words or syllables. We investigated the acoustic structure of syllables produced by young children and adults. Fricative-vowel syllables spoken by 40 subjects (eight adults and eight children at each of the ages 3, 4, 5, and 7 years) were analyzed acoustically to determine how well different syllables-initial fricatives were contrasted and how strongly they were affected by vocalic context. Results indicated two independent developmental trends: The extent to which speakers differentiated between /integral of/ and /s/ increased with age, while the extent to which they coarticulated each fricative with its following vowel decreased. The results support the hypothesis that children initially organize their speech gestures over a domain at least the size of the syllable and only gradually differentiate the syllable into patterns of gestures more closely aligned with its perceived segmental components.

Adult↗