Frequency-discrimination ability of hearing-impaired listeners.
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The chest wall vibrations generated by phonation were examined with respect to origin, amplitude, and spectrum in seven singers. The vibrations were picked up in male and female singer subjects by means of small accelerometers, which were fastened to the skin on the center of the sternum, and, for the purpose of comparison, on the thyroid cartilage and on the trachea a few cm below the larynx. Among the factors which influence the chest wall vibrations, the subglottal pressure oscillations seem to represent the most important excitation, while the mechanical shocks from the vocal fold vibrations seem secondary. Supra- and subglottal resonances seem moderately influential. The results of the investigation suggest that it is the voice source, particularly the amplitude of its fundamental, which is reflected in the chest wall vibrations. The amplitude of these vibrations seem to lie above the threshold of the Pacinian receptors for vibratory sensation as long as the fundamental frequency is below approximately 300 Hz. The amplitude of the voice source fundamental and hence the sensation of chest vibrations vary considerably as phonation is changed along the phonatory dimension which ranges from "pressed/tense/strained" through "flow" to "breathy" phonation. For this reason it seems likely that the sensation of chest vibrations can serve as a useful nonauditory and hence room-independent signal for the voluntary control of phonation.
Two-tone unmasking, psychophysical tuning curves and pure-tone masking patterns were measured at 500 and 1000 Hz in 17 listeners having high-frequency sensorineural hearing loss due to noise exposure. Results were compared to similar data obtained from 20 normal-hearing young adults. In addition, measures of word-recognition ability were obtained in quiet and in noise for both groups. The primary findings were as follows: (a) 29% (n = 5) of the hearing-impaired subjects exhibited abnormal results on at least one of the psychoacoustic tasks investigated; (b) the observed abnormalities were reliable; and (c) there appeared to be a relation between the presence of midfrequency dysfunction and degree of difficulty on word-recognition tasks. These results and their implications are discussed.
The ultimate goal of hearing aid selection procedures is successful use of amplification in everyday communication. The need to validate selection procedures is widely recognized, but the development of relevant criterion measures is a prerequisite to evaluation of predictive validity. This study explored the feasibility of using a self-report method of measuring success with amplification. A 64-item questionnaire was administered to 128 experienced hearing aid users who rated the benefit received from amplification in a variety of situations. Internal consistency reliability was excellent (alpha = .96), indicating that the perceived benefit is sufficiently consistent across situations to yield reliable measures of individual differences among patients. Factor analysis of the interitem correlation matrix, however, led to the identification of four types of situations that might be assessed separately: (a) noisy situations; (b) quiet situations with the speaker in proximity; (c) situations with reduced signal information; and (d) situations with nonspeech stimuli. In general, patients reported significantly more benefit from their aids in quiet situations than in noise. A self-report methodology for measuring successful use of amplification in daily life appears promising as a criterion measure in predictive validation studies of hearing aid selection procedures.
Two experiments were performed for this study. The purpose of both experiments was to examine the validity of pure-tone hearing thresholds obtained near the rising portion of a sensorineural hearing loss. Recent work by other investigators has suggested that thresholds obtained near the rising portion of the audiogram may not correspond to the severity of damage at the cochlear place associated with the test frequency. In the first experiment this issue was addressed in 11 subjects having low-frequency sensorineural hearing loss, whereas 12 subjects (19 ears) having notch-shaped high-frequency sensorineural hearing losses were examined in the second experiment. The results indicated that thresholds obtained from the rising portion of the audiometric configuration were, in most instances, determined by sensitivity at test frequency. An exception to this generalization involved low-frequency sensorineural hearing loss with a slope for the rising portion of the audiogram exceeding -25 dB/octave. In these cases the severity of the loss may be underestimated for test frequencies immediately adjacent to the rising portion of the audiogram.
Frequency discrimination for 500- and 2000-Hz pure tones at durations of 5, 10, 20, 50, and 200 ms was determined for 10 normal-hearing and 10 cochlear-impaired listeners. Listeners from both groups demonstrated monotonic increases in frequency difference limens as stimulus duration decreased. The functions of the hearing-impaired listeners were parallel to those of the normal-hearing listeners for stimulus durations between 10 and 200 ms, but the overall performance of the hearing-impaired group was poorer than that of the normal-hearing group. The functions of many of the cochlear-impaired subjects were less steep than normal for the shortest durations tested (between 5 and 10 ms). There appeared to be no relation between temporal integration for frequency discrimination and temporal integration for detection threshold. The results are discussed in terms of processes of temporal integration and frequency selectivity.
The influence that repeated tympanometric trials have on the aural-acoustic admittance characteristics of the middle-ear transmission system was studied in 24 young adults. The 226-Hz and 678-Hz data were generated by concurrently digitizing the conductance and admittance tympanograms at 25 daPa/s for both ascending and descending pressure directions. Ten successive trials for each frequency and direction of pressure change were made. Changes in admittance corrected for ear canal volume across the 10 tympanometric trials were computed. The results demonstrated that generally admittance increases as the number of trials increases. For many subjects, the complexity of the tympanometric configuration also increases across trials. The results from eight subjects with single-peaked 678-Hz tympanograms were compared with the results from eight subjects with notched 678-Hz tympanograms to explain the mean decrease in susceptance across tympanometric trials. Finally, the pressure peak locations of the conductance, susceptance, and admittance tympanograms were evaluated and are discussed. The effects that differences in peak pressure location have on the computed static admittance values are presented.
The relations between frequency selectivity and consonant intelligibility were investigated in subjects with sensorineural hearing loss in an attempt to derive predictive indices. Three matched pairs of subjects with similar audiometric configurations (high-frequency, flat or low-frequency hearing loss) but significantly different word-intelligibility scores were tested. Characteristics of psychophysical tuning curves (PTCs) for high- and low-frequency probes were compared with speech-intelligibility performance for high- and low-frequency consonant-vowel syllables. Frequency-specific relations between PTC characteristics and consonant-intelligibility performance were observed in the subject pairs with high-frequency and flat sensorineural hearing loss. Corresponding results for the subject pair with low-frequency sensorineural hearing loss were equivocal.
Five nonsingers and five singers vocally matched the pitches of frequency modulated tones. Subject responses to the shadowing task were analyzed in terms of accuracy, and in terms of duration and speed characteristics of pitch changes. In addition, each frequency change was categorized according to hit, overshoot, undershoot, or oscillate patterns. Singers were found to effect pitch changes in significantly less time than the nonsingers. This finding was attributed to more direct patterns (hits) and faster maximum speeds obtained by the singers. Both groups demonstrated a direct relationship between the size of the pitch change and each of the duration and speed parameters examined. Similarly, for both groups, pitch lowering was faster than pitch raising. Faster speeds and more direct paths in effecting pitch changes were viewed as evidence of greater vocal proficiency in singers as compared to nonsingers. Implications of the data for mechanical and physiological aspects of voice frequency control are discussed.
The purpose of this study was to employ measures of frequency resolution obtained from individual subjects to predict each subject's vowel recognition performance. Input filter patterns at six test frequencies were obtained from normal-hearing and hearing-impaired subjects. These patterns were used to correlate frequency resolution with vowel recognition in those same subjects. Vowels were presented at levels at which the entire spectrum was fully audible to each subject. Using each subject's measured filter characteristics (and interpolated values for intermediate frequencies), an "internal spectrum" of each vowel was calculated by determining the outputs of all filter channels for the vowel as the input signal. It was speculated that the more similar two internal spectra for a subject were, the more often they would be confused in the vowel recognition task. This expectation received some support when the measure of similarity was a point-by-point Euclidean distance between the two internal spectra. Stronger support was obtained when the measure of similarity was based upon Klatt's (1982) "weighted slope metric" that emphasizes similarities of spectral peak locations. The present study demonstrates a relation between impairments of frequency resolution and vowel recognition. The described filter-bank model of vowel recognition suggests that measures of frequency resolution along with the acoustic spectra of vowel stimuli may be useful in predicting the recognition of vowels by individuals.
Frequency modulation characteristics of sustained vowel phonations in vocal vibrato were investigated. Eight male singers produced sustained /a/ in vibrato at low-, middle-, and high-pitch levels with comfortable loudness. The recorded voice samples were digitized and analyzed by a program yielding a plot of fundamental frequencies (Fo) of individual fundamental cycles. Modulation frequency, extent, rates of Fo increase and decrease, and modulation jitter and modulation shimmer were measured for individual modulation cycles. Central tendency and variability of these measures, intercorrelations among these measures, and temporal patterns of frequency modulations were investigated. Results indicated (1) significant effects of pitch levels on modulation frequency, (2) more regularity in modulation frequency than extent, (3) predominantly linear temporal patterns of frequency modulation, and (4) faster Fo increase than decrease. Implications of these findings for the nature of underlying mechanisms of frequency control in vocal vibrato are discussed.
Children between 9 and 12 months of age were studied to determine if they would spontaneously imitate either the average fundamental frequency or the fundamental frequency contour of their speaking partners. In the first experiment, children were recorded at home as they interacted with their fathers and mothers. Acoustic analyses failed to reveal any tendency on the part of the infants to adjust vocal pitch, amplitude, or duration to those of their speaking partners. In a second experiment, children were recorded while interacting with their parents in a laboratory setting. Again, there were no indications that the children imitated the vocal patterns of their speaking partners.
A new method to calculate a spectral harmonics-to-noise ratio (HNR) in speech signals is presented. The method involves discrimination between harmonic and noise energy in the magnitude spectrum by means of a comb-liftering operation in the cepstrum domain. Sensitivity of HNR to (a) additive noise and (b) jitter was tested with synthetic vowel-like signals, generated at 10 fundamental frequencies. All jitter and noise signals were analyzed at three window lengths in order to investigate the effect of the length of the analysis frame on the estimated HNR values. Results of a multiple linear regression analysis with noise or jitter, F0, and window length as predictors for HNR indicate a major effect of both noise and jitter on HNR, in that HNR decreases almost linearly with increasing noise levels or increasing jitter. The influence of F0 and window length on HNR is small for the jittered signals, but HNR increases considerably with increasing F0 or window length for the noise signals. We conclude that the method seems to be a valid technique for determining the amount of spectral noise, because it is almost linearly sensitive to both noise and jitter for a large part of the noise or jitter continuum. The strong negative relation between HNR and jitter illustrates that spectral noise measures cannot simply be taken as indicators of the actual amount of noise in the time signal. Instead, HNR integrates several aspects of the acoustic stability of the signal. As such, HNR may be a useful parameter in the analysis of voice quality, although it cannot be directly interpreted in terms of underlying glottal events or perceptual characteristics.
Voice perturbation measures, such as jitter and shimmer, depend on accurate extraction of fundamental frequency (Fo) and amplitude of various waveform types. The extraction method directly affects the accuracy of the measures, particularly if several waveform types (with or without formant structure) are under consideration and if noise and modulation are present in the signal. For frequency perturbation, high precision is defined here as the ability to extract Fo to +/- 0.01% under conditions of noise and modulation. Three Fo-extraction methods and their software implementations are discussed and compared. The methods are cycle-to-cycle waveform matching, zero-crossing and peak-picking. Interpolation between samples is added to make the extractions more accurate and reliable. The sensitivity of the methods to different parameters such as sampling frequency, mean Fo, signal-to-noise ratio, frequency modulation, and amplitude modulation are explored.
It has been shown that visual display systems of intonation can be employed beneficially in teaching intonation to persons with deafness and in teaching the intonation of a foreign language. In this paper, the question is addressed whether important audible differences between two pitch contours correspond with visually conspicuous differences between displayed pitch contours. If visual feedback of intonation is to be effective in teaching situations, such correspondence must exist. In two experiments, phoneticians rated the dissimilarity of two pitch contours. In the first experiment they rated the two pitch contours auditorily (i.e., by listening to two resynthesized utterances). In the second, they rated the same two pitch contours visually (i.e., by looking at the two contours displayed on a computer screen). The results indicate why visual feedback may be very effective in intonation training if pitch contours are displayed in such a way that only auditorily relevant features are represented.
It has been shown that visual display systems of intonation can be employed beneficially in teaching intonation to persons with deafness and in teaching the intonation of a foreign language. In current training situations the correctness of a reproduced pitch contour is rated either by the teacher or automatically. In the latter case an algorithm mostly estimates the maximum deviation from an example contour. In game-like exercises, for instance, the pupil has to produce a pitch contour within the displayed floor and ceiling of a "tunnel" with a preadjusted height. In an experiment described in the companion paper, phoneticians had rated the dissimilarity of two pitch contours both auditorily, by listening to two resynthesized utterances, and visually, by looking at two pitch contours displayed on a computer screen. A test is reported in which these dissimilarity ratings were compared with automatic ratings obtained with this tunnel measure and with three other measures, the mean distance, the root-mean-square (RMS) distance, and the correlation coefficient. The most frequently used tunnel measure appeared to have the weakest correlation with the ratings by the phoneticians. In general, the automatic ratings obtained with the correlation coefficient showed the strongest correlation with the perceptual ratings. A disadvantage of this measure, however, may be that it normalizes for the range of the pitch contours. If range is important, as in intonation teaching to persons with deafness, the mean distance or the RMS distance are the best physical measures for automatic training of intonation.
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.
This study investigated maturational changes in children's ability to discriminate the frequency of short-duration tone pulses. Frequency difference limens (DLs) were measured for digitally generated 1000-Hz tones with pulse durations of 200, 50, and 20 ms using a two-alternative, two-interval, forced-choice procedure. Participants were 16 5-year-old children; 10 children each in the age categories of 7, 9, and 11 years; and a control group of 10 young adults. Eleven of the 5-year-old children were unable to learn the experimental task. All children in the three older groups and the adults successfully completed the study. The five 5-year-old children who completed the task performed similarly to the 7-year-old children. All groups of participants showed an inverse relationship between duration of the signal and the size of the DL. The DLs at all three tone durations were significantly larger for the 7-year-old children than they were for the older children and adults. There were no significant differences in DL size among the 9-year-old, 11-year-old, and adult subjects at any tone duration. These findings suggest that the sensory and/or cognitive skills required to discriminate the frequency of brief-duration tones may not reach maturity until after age 7 years.