Acoustical-perceptual correlates of "whisper pitch" in synthetically generated vowels.

The purpose of this investigation was to clarify acoustical-perceptual relationships in identification of "pitch" during whispered vowel production. The experimenters systematically varied selected acoustic features of synthetically generated "whispered" vowels to control which formant frequencies were shifted (F1, F2, or F1&F2), the direction of formant frequency shifts (up or down), and the magnitude of formant frequency shifts (20 Hz, 40 Hz, 60 Hz). Two sets of stimuli were produced to simulate the resonance characteristics of the vowel /a/: one set for male talkers and one for female talkers. Ninety-four pairs of synthesized vowel tokens were randomly presented to 17 listeners who judged if the "pitch" of the second member of the pair was the same, higher, or lower than the "pitch" of the first member. The results showed an inverse relationship between the magnitude of formant frequency changes presented to the judges and the number of perceptual mismatches in "whisper pitch." Also, fewer mismatches in the identification of whisper pitch occurred when both F1 and F2 were changed simultaneously than when either F1 or F2 was changed individually. No differences were found between the perceptual responses to "male" and "female" vowel simulations. The primary implication of this study is that whisper pitch is more influenced by simultaneous changes in F1 and F2 than by changes in only one of the formants.

Consonant-vowel interdependencies in babbling and early words: preliminary examination of a locus equation approach.

Consonant-vowel productions at two distinct stages of language development were studied in a single female child. At 12 months canonical babbling syllables (N = 144) identified by a panel of listeners as comprising [bV], [dV], and [gv] tokens were acoustically analyzed by measuring F2 transition onset and F2 midvowel frequencies and plotting their relationship as locus equations for each stop category. A regression analysis performed on these scatterplots revealed differential slopes and y-intercepts as a function of stop place. The same analysis was performed 9 months later on CV utterances (N = 243) produced as syllable-initial segments of real words by the same child. Whereas labial and velar locus equation parameters moved toward more adult-like values, alveolar slope and y-intercept moved away from adult values and more in the direction of decreased coarticulation between vowel and consonant. There was greater scatter of data points around the regression line for production of words compared to babbling. These results are compared to locus equations obtained from 3-5-year-olds and adults. Locus equations appear to be useful as an empirical developmental probe to document how CV productions gradually approach adult categorical standards.

Measures of vocal function during changes in vocal effort level.

The purpose of this article is to present the results of a controlled study of the day-to-day variabilities of three acoustic parameters (jitter, shimmer, and normalized noise energy), and two electroglottographic parameters (contact quotient and contact quotient perturbation) for vowels produced at three vocal efforts (low, normal, high). Data were obtained with use of a sophisticated bilinear interpolation pitch detection method. A repeated measures design required subjects to produce the vowels /ae/ and /a/ five times a day over 3 days at each vocal effort level. The jitter, shimmer, and normalized noise energy values from acoustic measures and contact quotient and contact quotient perturbation values varied significantly among the three vocal effort levels. The clinical implication of this finding is that vocal effort must be controlled in order to obtain consistent clinical measures. Furthermore, day-to-day variability must be taken into account if representative measures are to be obtained for clinical use.

Effects of temporal alterations on speech intelligibility in parkinsonian dysarthria.

The effect of two types of temporal alterations, paced and synthetic, on the intelligibility of parkinsonian dysarthric speech was investigated. Six speakers with idiopathic Parkinson's disease served as subjects. Paced temporal alterations were created by slowing each speaker to 60% of his/her habitual speaking rate. The synthetic alterations were created by modifying the habitual rate speech samples using digital signal processing. Three types of synthetic alterations were examined: Pause Altered, Speech Duration Altered, and Pause and Speech Duration Altered. The 60% of habitual speaking rate condition was more intelligible than the synthetic conditions. In addition, none of the synthetic alterations were found to be more intelligible than samples produced at habitual speaking rates. The results suggest that simple alterations of speech signals do not explain the differences in intelligibility that have been observed when parkinsonian dysarthric speakers reduce speaking rates. Reasons for the failure of synthetic alterations to increase speech intelligibility scores are discussed.

Acoustical effects of endotracheal intubation.

Certain acoustical consequences of endotracheal intubation were examined in 13 male cardiovascular-surgery patients. Each subject recorded three tokens of a sustained vowel 1 day before intubation, 1 day after, upon discharge, and during a follow-up visit. Eight acoustical measures were obtained from the audio-recorded vowels: (a) mean fundamental frequency (Fo), (b) Fo standard deviation, (c) Fo perturbation quotient, (d) mean sound pressure level (SPL), (e) SPL standard deviation, (f) SPL perturbation quotient, (g) spectral flatness of the residue signal, and (h) coefficient of excess. Mean Fo, Fo standard deviation, mean SPL, SPL standard deviation, and coefficient of excess did not differ significantly across recording sessions, although certain predictable trends were apparent. Fo perturbation quotient, SPL perturbation quotient, and spectral flatness of the residue signal varied significantly across sessions, implying that these acoustical measures may be useful in the identification and monitoring of even minor intubation-related laryngeal trauma.

Tempo of spectrum change as a cue in speech-sound discrimination by infants.

Six- to seven-month-old infants were tested on their ability to discriminate among three speech sounds which differed on the basis of formant-transition duration, a major cue to distinctions among stop, semivowel and diphthong classes. The three speech sounds, [see text] were produced in two different ways. The stimuli for one experiment were two-formant synthetic tokens which differed in formant-transition duration. The stimuli for a second experiment was produced with a computer-modification technique which artificially shortened or lengthened the formant-transition portion of a naturally produced [see text], resulting in tokens of [see text]. The discrimination procedure involved visual reinforcement of a head-turn response following a change from a repeating background stimulus to a contrasting stimulus. Infants in both experiments discriminated [see text]; evidence for [see text] discrimination was obtained for the "computer modified" tokens only. These findings are discussed in terms of possible mechanisms underlying speech perception in infancy.

An ultrasonic--EMG transducer for biodynamic research.

This note describes a newly developed single-element muscle action potential/motion transducer. The transcuer was specially designed for speech research. Techniques for use of the transducer are described. Sample data are presented illustrating the capability of the transducer, and applications of the device are discussed.

Rhythm and syllable timing in phrase level stress patterning.

The rhythm of syllables in repetitions of a phrase was measured with a finger-tapping task. These rhythm measurements were shown to vary with phrase level stress patterning. However, this relationship was not invariant. Acoustic measurements of the time between syllables showed stress pattern relationships similar to those observed in the rhythm-tapping task. The temporal differences between stress patterns appear to be (1) evident even when acoustic measurements exclude syllable duration, (2) significant even at a fast speaking rate, and (3) variable between speakers.

Fricative discrimination in early infancy.

In three separate experiments using controlled natural stimuli and a high-amplitude sucking paradigm, infants' ability to detect differences between /s/ and /v/, /s/ and /f/, and /s/ and /z/, respectively, was investigated. Evidence for discrimination was obtained for /s/ versus /v/ and /s/ versus /f/ but not for /s/ versus /z/. Implications for a theory of infant speech perception are discussed.