Dissociations between vowel durations and formant frequency characteristics

Disagreement exists on the degree to which rate of speech and segmental duration affect the formant frequency characteristics of vowels. Post hoc analysis of the vowel characteristics of words uttered by women in conversational speech with both adult and child addressees indicates that there is no simple relationship between the length of vowels and the degree to which their formant frequency characteristics resemble those seen in citation forms of speech. In the case of women addressing children, it was possible for content and function words to share formant frequency characteristics that maximally differentiated their embedded vowels, despite the relatively shorter duration of function word vowels. Implications for the elicitation of "clear speech" are discussed.     

Examination of the neighborhood activation theory in normal and hearing-impaired listeners

OBJECTIVE: Experiments were conducted to examine the effects of lexical information on word recognition among normal hearing listeners and individuals with sensorineural hearing loss. The lexical factors of interest were incorporated in the Neighborhood Activation Model (NAM). Central to this model is the concept that words are recognized relationally in the context of other phonemically similar words. NAM suggests that words in the mental lexicon are organized into similarity neighborhoods and the listener is required to select the target word from competing lexical items. Two structural characteristics of similarity neighborhoods that influence word recognition have been identified; "neighborhood density" or the number of phonemically similar words (neighbors) for a particular target item and "neighborhood frequency" or the average frequency of occurrence of all the items within a neighborhood. A third lexical factor, "word frequency" or the frequency of occurrence of a target word in the language, is assumed to optimize the word recognition process by biasing the system toward choosing a high frequency over a low frequency word. DESIGN: Three experiments were performed. In the initial experiments, word recognition for consonant-vowel-consonant (CVC) monosyllables was assessed in young normal hearing listeners by systematically partitioning the items into the eight possible lexical conditions that could be created by two levels of the three lexical factors, word frequency (high and low), neighborhood density (high and low), and average neighborhood frequency (high and low). Neighborhood structure and word frequency were estimated computationally using a large, on-line lexicon-based Webster's Pocket Dictionary. From this program 400 highly familiar, monosyllables were selected and partitioned into eight orthogonal lexical groups (50 words/group). The 400 words were presented randomly to normal hearing listeners in speech-shaped noise (Experiment 1) and "in quiet" (Experiment 2) as well as to an elderly group of listeners with sensorineural hearing loss in the speech-shaped noise (Experiment 3). RESULTS: The results of three experiments verified predictions of NAM in both normal hearing and hearing-impaired listeners. In each experiment, words from low density neighborhoods were recognized more accurately than those from high density neighborhoods. The presence of high frequency neighbors (average neighborhood frequency) produced poorer recognition performance than comparable conditions with low frequency neighbors. Word frequency was found to have a highly significant effect on word recognition. Lexical conditions with high word frequencies produced higher performance scores than conditions with low frequency words. CONCLUSION: The results supported the basic tenets of NAM theory and identified both neighborhood structural properties and word frequency as significant lexical factors affecting word recognition when listening in noise and "in quiet." The results of the third experiment permit extension of NAM theory to individuals with sensorineural hearing loss. Future development of speech recognition tests should allow for the effects of higher level cognitive (lexical) factors on lower level phonemic processing.     

Acoustic and perceptual characteristics of vowels produced during simultaneous communication

This study investigated the acoustical and perceptual characteristics of vowels in speech produced during simultaneous communication (SC). Twelve normal hearing, experienced sign language users were recorded under SC and speech alone (SA) conditions speaking a set of sentences containing monosyllabic words designed for measurement of vowel duration, formant frequencies, and fundamental frequency in consonant-vowel-consonant (CVC) syllables and 60 listeners audited the speech samples. Although results indicated longer sentence and vowel durations for SC than SA, the data showed no difference in spectral characteristics of vowels produced during SC versus SA, indicating no degradation of vowel spectrum by rate alteration during SC. Further, no difference was found in listeners' ability to identify vowels produced during SC versus SA, indicating no degradation of vowel perceptual cues during SC. These conclusions are consistent with previous research indicating that temporal alterations produced by SC do not produce degradation of segmental acoustical characteristics of spoken English. LEARNING OUTCOMES: As a result of this activity, the participant will be able to (1) describe simultaneous communication; (2) explain the role of simultaneous communication in communication with children who are deaf; (3) describe vowel acoustics in English speech; (4) discuss methods of measuring vowel perception; (5) specify the acoustic characteristics of vowels produced during simultaneous communication; and (6) specify the ability of listeners to perceive vowels in speech produced during simultaneous communication.     

Acoustical analysis of Spanish vowels produced by laryngectomized subjects.

The purpose of this study was to describe the acoustic characteristics of Spanish vowels in subjects who had undergone a total laryngectomy and to compare the results with those obtained in a control group of subjects who spoke normally. Our results are discussed in relation to those obtained in previous studies with English-speaking laryngectomized patients. The comparison between English and Spanish, which diFfer widely in the size of their vowel inventories, will help us to determine specific or universal vowel production characteristics in these patients. Our second objective was to relate the acoustic properties of these vowels to the perceptual data obtained in our previous work (J. L. Miralles & T. Cervera, 1995). In that study, results indicated that vowels produced by alaryngeal speakers were well perceived in word context. Vowels were produced in CVCV word context by two groups of patients who had undergone laryngectomy: tracheoesophageal speakers (TES) and esophageal speakers. In addition a control group of normal talkers was included. Audio recordings of 24 Spanish words produced by each speaker were analyzed using CSL (Kay Elemetrics). Results showed that F1, F2, and vowel duration of alaryngeal speakers differ significantly from normal values. In general, laryngectomized patients produce vowels with higher formant frequencies and longer durations than the group of laryngeal subjects. Thus, the data indicate modifications either in the frequency or temporal domain, following the same tendency found in previous studies with English-speaking laryngectomized speakers.     

The impact of lexical factors on children's word-finding errors.

This retrospective, exploratory investigation examined the types of target words that 30 children with word-finding difficulties (aged 8 to 12 years) had difficulty naming and the types of errors they made on these words. Words were studied with reference to lexical factors that might influence naming performance: word frequency, age of acquisition, familiarity, and lexical neighborhood. Findings indicated that neighborhood density predicted word-finding success, and target word substitutions and error patterns manifested were affected by the lexical factors under study. Students tended to produce substitutions that were higher in frequency, learned earlier, and that resided in neighborhoods of greater density and higher frequency than the target word. Lexical factors also influenced children's error patterns. Neighborhood density predicted form-related errors: Children produced more blocked errors on words from sparse neighborhoods. Word frequency and neighborhood frequency predicted form-segment-related errors as phonologic errors occurred on rare words and words whose neighbors contained lower frequency, uncommon phonological patterns. This important first step in the examination of how lexical factors have an impact on word-finding errors in children suggests that different types of words are more likely to result in failures of lexical access at different stages of processing. Theoretical and practical implications of these preliminary findings are discussed.     

Acoustic differences between content and function words in amyotrophic lateral sclerosis.

Studies describing acoustic characteristics of speech produced by individuals with dysarthria may help to explain intelligibility deficits for these speakers. One goal of the current study was to investigate the manner and extent to which nine speakers with mild to moderate dysarthria associated with amyotrophic lateral sclerosis (ALS) and nine healthy speakers acoustically distinguished /i/, /ae/, /u/, and /a/ in content and function words. A further aim was to evaluate the relationship between impaired speech in ALS and the magnitude of acoustic differences for vowels in content and function words. Speakers read the Farm Passage at a comfortable or habitual rate. F1 and F2 midpoint frequencies were measured, and vowel space areas were calculated. Vowel durations also were measured. The magnitude of F1, F2, vowel space area, and duration differences for vowels in content and function words was not statistically different for speakers with ALS and healthy controls. In addition, with the exception of /i/ produced by some speakers with ALS, vowel duration tended to be shorter in function words. Average F1 and F2 values for function words also tended to be centralized relative to content words. Although vowel space area differences for the two speaker groups were not statistically significant, there was a tendency for the difference in vowel space area for content and function words to be smaller for speakers with ALS than for controls. Regression analyses further indicated that the magnitude of temporal differences for vowels in content and function words was a better predictor of impaired speech than the magnitude of spectral differences for vowels in content and function words. One clinical implication is that individuals with ALS may benefit from therapy techniques targeting temporal properties of the acoustic signal.     

Phonological neighborhood and word frequency effects in the stuttered disfluencies of children who stutter.

PURPOSE: The purpose of this study was to examine (a) the role of neighborhood density (number of words that are phonologically similar to a target word) and frequency variables on the stuttering-like disfluencies of preschool children who stutter, and (b) whether these variables have an effect on the type of stuttering-like disfluency produced. METHOD: A 500+ word speech sample was obtained from each participant (N = 15). Each stuttered word was randomly paired with the firstly produced word that closely matched it in grammatical class, familiarity, and number of syllables/phonemes. Frequency, neighborhood density, and neighborhood frequency values were obtained for the stuttered and fluent words from an online database. RESULTS: Findings revealed that stuttered words were lower in frequency and neighborhood frequency than fluent words. Words containing part-word repetitions and sound prolongations were also lower in frequency and/or neighborhood frequency than fluent words, but these frequency variables did not have an effect on single-syllable word repetitions. Neighborhood density failed to influence the susceptibility of words to stuttering, as well as the type of stuttering-like disfluency produced. CONCLUSIONS: In general, findings suggest that neighborhood and frequency variables not only influence the fluency with which words are produced in speech, but also have an impact on the type of stuttering-like disfluency produced.     

Effect of syllable-initial voicing on vowel duration during simultaneous communication

Vowel durations following the production of voiced and voiceless stop consonants produced during simultaneous communication (SC) were investigated by recording sign language users during SC and speech alone (SA). Under natural speaking conditions, or speaking alone (SA), vowels following voiced stop consonants are longer in duration than vowels following voiceless stops. Although the results indicated longer sentence durations for SC than SA, they showed no differences in the relative duration of vowels following voiced or voiceless stops. Vowel durations following voiced stop consonants were consistently longer than vowel durations following voiceless stops. This finding is consistent with previous research indicating that global temporal alterations in SC do not degrade temporal or spectral cues of spoken English. LEARNING OUTCOMES: As a result of this activity, the participant will be able to (1) describe simultaneous communication; (2) explain the role of simultaneous communication in communication with persons who are hearing-impaired; (3) describe how the voicing characteristic of syllable-initial consonants affects the duration of subsequent vowels; and (4) explain that simultaneous communication does not influence the relative durations of vowels following voiced and voiceless stop consonants.     

Phonological pattern frequency and speech production in adults and children.

Recent studies have suggested that both adults and children are sensitive to information about phonological pattern frequency; however, the influence of phonological pattern frequency on speech production has not been studied extensively. The current study examined the effect of phonological pattern frequency on the fluency and flexibility of speech production. Normal- and fast- rate nonsense-word repetitions of three groups of participants (preschool children, school-aged children, and adults) were analyzed. Subjective ratings of the wordlikeness of nonsense words, percentage phonemes correctly repeated, mean duration, and durational variability were measured. In the first experiment, ratings of the wordlikeness of nonsense words were found to correlate with the pattern frequency of sequences embedded in them. In the second analysis, it was found that children, but not adults, repeated infrequent sequences of phonemes less accurately than frequent sequences. In the third experiment, infrequent sequences were produced with longer durations than frequent ones, with children demonstrating a larger difference between frequent and infrequent sequences than adults. Phonological pattern frequency also influenced variability in duration: infrequent sequences of sounds were more variable than frequent ones. Thus, there appears to be an influence of phonological pattern frequency on speech, and, for some measures, a larger effect size is noted for children.     

Talker differences in clear and conversational speech: acoustic characteristics of vowels.

PURPOSE: To determine the specific acoustic changes that underlie improved vowel intelligibility in clear speech. METHOD: Seven acoustic metrics were measured for conversational and clear vowels produced by 12 talkers-6 who previously were found (S. H. Ferguson, 2004) to produce a large clear speech vowel intelligibility effect for listeners with normal hearing identifying vowels in background noise (the big benefit talkers), and 6 who produced no clear speech vowel intelligibility benefit (the no benefit talkers). RESULTS: For vowel duration and for certain measures of the overall acoustic vowel space, the change from conversational to clear speech was significantly greater for big benefit talkers than for no benefit talkers. For measures of formant dynamics, in contrast, the clear speech effect was similar for the 2 groups. CONCLUSION: These results suggest that acoustic vowel space expansion and large vowel duration increases improve vowel intelligibility. In contrast, changing the dynamic characteristics of vowels seems not to contribute to improved clear speech vowel intelligibility. However, talker variability suggested that improved vowel intelligibility can be achieved using a variety of clear speech strategies, including some apparently not measured here.     

The effect of stimulus duration on perception of Turkish vowels in normal-hearing and hearing-impaired children

The objective of the study was to examine the effects of stimulus duration on vowel perception in normal-hearing and hearing-impaired children. For this purpose, 80 semisynthetic vowel stimuli consisting of eight different Turkish vowels with ten different durations were presented to 14 normal-hearing and 15 hearing impaired children, and they were asked to identify the vowel they heard. Thirteen normal-hearing adults served as speaker subjects to get normative data on mean durations of the Turkish vowels. While there was no significant effect of duration on perception in normal-hearing children, perception errors for very short and very long vowels were observed in hearing-impaired children. The most frequent responses as a function of duration showed four different patterns: (1) three vowels were perceived correctly in all durations; (2) two were perceived correctly in middle and longer durations; (3) two were perceived correctly in middle duration; and (4) only one was perceived correctly in short duration. It was concluded that the effects of stimulus duration on vowel perception were determined by natural duration of the vowel in a given language, and unnaturally short and long vowels were misperceived by hearing impaired subjects.     

Phonological space in the speech of the hearing impaired

The vowels /a/, /i/, and /u/ form the extreme points of vowel triangle in Kannada language. First and second formant frequencies of these vowels were measured to determine the phonological space in the speech of the 30 deaf subjects and 30 normally hearing subjects. The phonological space was found to be reduced in the speech of the hearing-impaired subjects, and the reduction was primarily due to the lowering of the second formant of the vowel /i/. Therapeutic implications have been drawn.     

Voice onset time, frication, and aspiration in word-initial consonant clusters.

The voice onset time (VOT) and the duration of the burst of frication noise at the release of a plosive consonant were measured from spectrograms of word-initial consonant clusters. Mean data from three speakers reading English words in a sentence frame indicated that the VOT changed as a function of the place of articulation of the plosive and as a function of the identity of the following vowel or sonorant consonant. Burst durations varied in a similar way such that the remaining interval of aspiration in /p, t, k/ was nearly the same duration in comparable phonetic environments. The VOT was longer before sonorants and high vowels than before mid- and low vowels. Aspiration was also seen in an /s/-sonorant cluster. To explain these regularities, production strategies and perceptual cues to a voicing decision for English plosives are considered. Variations in VOT are explained in terms of articulatory mechanisms, perceptual constraints, and phonological rules. Some VOT data obtained from a connected discourse were also analyzed and organized into a set of rules for predicting voice onset time in any sentence context.     

Feature characteristics of spontaneous speech production in young deaf children

Sixty-five 6-yr-old deaf children from state supported schools were given an adaptation of the Goldman Fristoe test of articulation to assess their spontaneous speech production. Responses were measured in terms of features of manner, place, voice visibility, position, and error type and compared to imitative samples. A rank order of difficulty for each phoneme, error type, and word position is presented. Results show that of the phonemes, low back vowels, diphthongs, laterals, and voiced consonants were more easily produced. A relationship could be found between fundamental frequency, formant frequency, intensity, and phoneme production, suggesting that these variables and features may be providing the governance underlying the phonological rules in the development of speech in the deaf. Suggestions for training are given.     

Vowel space characteristics and vowel identification accuracy.

PURPOSE: To examine the relation between vowel production characteristics and intelligibility. METHOD: Acoustic characteristics of 10 vowels produced by 45 men and 48 women from the J. M. Hillenbrand, L. A. Getty, M. J. Clark, and K. Wheeler (1995) study were examined and compared with identification accuracy. Global (mean f0, F1, and F2; duration; and amount of formant movement) and fine-grained measures (vowel space area; mean distance among vowels; f0, F1, and F2 ranges; duration ratio between long and short vowels; and formant movement ratio between dynamic and static vowels) were used to predict identification scores. Acoustic measures of the most frequently confused pairs (/ae/-/epsilon/ and /a/-/inverted v/) were compared. RESULTS: Global and fine-grained measures accounted for less than 1/4 of variance in identification scores: Vowel space area alone accounted for 9%-12% of variance. Differences in vowel identification were largely due to poor identification of /ae/, /epsilon/, /a/, or /inverted v/. Well-identified vowels were distinctive in formant frequencies, duration, and amount of formant movement over time. CONCLUSIONS: Distinctiveness among neighboring vowels is more important in determining vowel intelligibility than vowel space area. Acoustic comparison of confused vowels may be more useful in studying intelligibility of normal and disordered speech than in measuring vowel space area.     

Training effects on vowel production by two profoundly hearing-impaired speakers

Two profoundly hearing-impaired adolescents received systematic speech training to improve their production of the vowels /i/ and /ae/. Acoustic measures of F1, F2, and duration, and listener judgements of vowel acceptability, were used to quantify vowel production before and after training. Both subjects demonstrated significant changes in their production of the two vowels at the acoustic and perceptual levels following treatment. The changes were highly individualized. For some features, significant improvement occurred posttreatment with differences between the hearing-impaired subject and a control group of subjects with normal hearing no longer present. There was a significant improvement in the acceptability of the two vowels in each subject's speech after training. Vowel duration remained unchanged in the speech of one subject whereas it increased in the speech of the other subject following training. There was a trend toward reduced token-to-token variation in the posttreatment samples. Acoustic and perceptual measures also were obtained on two vowels not directly trained in the program. Significant changes occurred in the production of these segments but some of the changes resulted in greater deviation in the post- than in the pretreatment samples.     

Lexical representations in children with SLI: evidence from a frequency-manipulated gating task.

PURPOSE: This study investigated lexical representations of children with specific language impairment (SLI) and typically developing, chronological age-matched (CA) peers on a frequency-manipulated gating task. The study tested the hypothesis that children with SLI have holistic phonological representations of words, that is, that children with SLI would exhibit smaller effects of neighborhood density on gating durations than CA peers and that children with SLI would be as efficient as CA peers in accessing high-frequency words but that they would differ from their age-matched peers in accessing low-frequency words. METHOD: Thirty-two children (ages 8;5-12;3 [years;months]) participated: 16 children with SLI and 16 typically developing peers matched on age and nonverbal IQ. Children's word guesses after different gating durations were investigated. RESULTS: Contrary to predictions, no group differences in effects of distributional regularity were found: Children in both groups required equally longer acoustic chunks to access words that were low in frequency and came from dense neighborhoods. However, children with SLI appeared to vacillate between multiple word candidates at significantly later gates when compared with children in the CA group. CONCLUSIONS: Children with SLI did not exhibit evidence for phonologically holistic lexical representations. Instead, they appeared more vulnerable to competing words.     

Speech and phonological characteristics of individual children with a history of tracheostomy.

The present investigation studied the speech production and phonological skills of 6 children between the ages of 2;8 and 6;8 (years;months) who had undergone tracheostomy before age 8 months. Each child's speech was analyzed for size and composition of phonetic inventory, use of phonological processes, production of vowels, and production of the voicing contrast for stops. Analyses were completed once consistent air support for vocalization was established for each child and 3 months after that date. This study highlights the slow development of sound acquisition, vowel production, and the distinction between voiced and voiceless stops for some, but not all, children with a history of tracheostomy. Each child exhibited his or her own pattern of speech production difficulties on four tasks. Excessive use of inappropriate phonological processes relative to age was the most prevalent speech production problem. Five of 6 subjects exhibited clinically significant use of Stridency Deletion, Liquid Deviation, and/or Cluster Reduction. Adjustments were noted in the speech of all subjects during a 3-month period.