Biomedical subjects

D D Dirks

Publications and source records attributed to D D Dirks.

At least 19 recordsLinked to original sources

PubMed1992

Frequency-importance functions for words in high- and low-context sentences.

The relative importance and absolute contributions of various spectral regions to speech intelligibility under conditions of either neutral or predictable sentential context were examined. Specifically, the frequency-importance functions for a set of monosyllabic words embedded in a highly predictive sentence context versus a sentence with little predictive information were developed using Articulation Index (AI) methods. Forty-two young normal-hearing adults heard sentences presented at signal-to-noise ratios from -8 to +14 dB in a noise shaped to conform to the peak spectrum of the speech. Results indicated only slight differences in 1/3-octave importance functions due to differences in semantic context, although the crossovers differed by a constant 180 Hz. Methodological and theoretical aspects of parameter estimation in the AI model are discussed. The results suggest that semantic context, as defined by these conditions, may alter frequency-importance relationships in addition to the dynamic range over which intelligibility rises.

Adolescent↗

PubMed1990

Associations among frequency and temporal resolution and consonant recognition for hearing-impaired listeners.

To examine the association between frequency and temporal resolution and speech recognition, auditory filter parameters, rates of masking decay, and stop-consonant recognition were determined for 9 normal-hearing and 24 hearing-impaired subjects. Speech-presentation levels were selected for each subject based on articulation index (AI) predictions. Results suggest that auditory filter widths and dynamic ranges were strongly correlated with pure-tone threshold, while time constants were not. Stop-consonant recognition scores for most hearing-impaired listeners were not significantly poorer than predicted by the AI model. Furthermore, differences between observed recognition scores and those predicted by the AI were poorly correlated with derived psychophysical parameter values, suggesting that measures of frequency and temporal resolution and speech recognition may appear to be associated primarily because of their dependence on auditory threshold.

Adult↗

PubMed1989

Closed-set effects in consonant confusion patterns.

Invariance of error patterns in confusion matrices of varying dimensions were examined. Normal-hearing young adults were presented closed-set arrangements of digitized syllable tokens, spoken by 1 male and 1 female talker, and selected from a set of 14 consonants (stops and fricatives). Each consonant was paired with the vowel/a/ in a vowel-consonant format and presented at three intensity levels. Patterns of errors among voiceless stops and among voiced fricatives were dependent on the set of alternatives. Voiceless fricatives and voiced stops were not significantly affected by the number of response alternatives. Speaker differences, individual differences among listeners, and implications relating to the generalization of confusion data collected in small closed-set arrangements are discussed.

Adolescent↗

PubMed1989

Interactive factors in consonant confusion patterns.

Confusion patterns among English consonants were examined using log-linear modeling techniques to assess the influence of low-pass filtering, shaped noise, presentation level, and consonant position. Ten normal-hearing listeners were presented consonant-vowel (CV) and vowel-consonant (VC) syllables containing the vowel /a/. Stimuli were presented in quiet and in noise, and were either filtered or broadband. The noise was shaped such that the effective signal level in each 1/3 octave band was equivalent in quiet and noise listening conditions. Three presentation levels were analyzed corresponding to the overall rms level of the combined speech stimuli. Error patterns were affected significantly by presentation level, filtering, and consonant position as a complex interaction. The effect of filtering was dependent on presentation level and consonant position. The effects stemming from the noise were less pronounced. Specific confusions responsible for these effects were isolated, and an acoustical interaction is suggested, stressing the spectral characteristics of the signals and their modification by presentation level and filtering.

Adult↗

PubMed1989

Stop-consonant recognition for normal-hearing listeners and listeners with high-frequency hearing loss. I: The contribution of selected frequency regions.

The purpose of this study is to specify the contribution of certain frequency regions to consonant place perception for normal-hearing listeners and listeners with high-frequency hearing loss, and to characterize the differences in stop-consonant place perception among these listeners. Stop-consonant recognition and error patterns were examined at various speech-presentation levels and under conditions of low- and high-pass filtering. Subjects included 18 normal-hearing listeners and a homogeneous group of 10 young, hearing-impaired individuals with high-frequency sensorineural hearing loss. Differential filtering effects on consonant place perception were consistent with the spectral composition of acoustic cues. Differences in consonant recognition and error patterns between normal-hearing and hearing-impaired listeners were observed when the stimulus bandwidth included regions of threshold elevation for the hearing-impaired listeners. Thus place-perception differences among listeners are, for the most part, associated with stimulus bandwidths corresponding to regions of hearing loss.

Adult↗

PubMed1989

Stop-consonant recognition for normal-hearing listeners and listeners with high-frequency hearing loss. II: Articulation index predictions.

Articulation index (AI) theory was used to evaluate stop-consonant recognition of normal-hearing listeners and listeners with high-frequency hearing loss. From results reported in a companion article [Dubno et al., J. Acoust. Soc. Am. 85, 347-354 (1989)], a transfer function relating the AI to stop-consonant recognition was established, and a frequency importance function was determined for the nine stop-consonant-vowel syllables used as test stimuli. The calculations included the rms and peak levels of the speech that had been measured in 1/3 octave bands; the internal noise was estimated from the thresholds for each subject. The AI model was then used to predict performance for the hearing-impaired listeners. A majority of the AI predictions for the hearing-impaired subjects fell within +/- 2 standard deviations of the normal-hearing listeners' results. However, as observed in previous data, the AI tended to overestimate performance of the hearing-impaired listeners. The accuracy of the predictions decreased with the magnitude of high-frequency hearing loss. Thus, with the exception of performance for listeners with severe high-frequency hearing loss, the results suggest that poorer speech recognition among hearing-impaired listeners results from reduced audibility within critical spectral regions of the speech stimuli.

Adult↗

PubMed1989

Auditory filter characteristics and consonant recognition for hearing-impaired listeners.

To examine the association between frequency resolution and speech recognition, auditory filter parameters and stop-consonant recognition were determined for 9 normal-hearing and 24 hearing-impaired subjects. In an earlier investigation, the relationship between stop-consonant recognition and the articulation index (AI) had been established on normal-hearing listeners. Based on AI predictions, speech-presentation levels for each subject in this experiment were selected to obtain a wide range of recognition scores. This strategy provides a method of interpreting speech-recognition performance among listeners who vary in magnitude and configuration of hearing loss by assuming that conditions which yield equal audible spectra will result in equivalent performance. It was reasoned that an association between frequency resolution and consonant recognition may be more appropriately estimated if hearing-impaired listeners' performance was measured under conditions that assured equivalent audibility of the speech stimuli. Derived auditory filter parameters indicated that filter widths and dynamic ranges were strongly associated with threshold. Stop-consonant recognition scores for most hearing-impaired listeners were not significantly poorer than predicted by the AI model. Furthermore, differences between observed recognition scores and those predicted by the AI were not associated with auditory filter characteristics, suggesting that frequency resolution and speech recognition may appear to be associated primarily because both are degraded by threshold elevation.

Adolescent↗

PubMed1987

Basic acoustic considerations of ear canal probe measurements.

This publication contains a review of several acoustic investigations in which the effects of probe location on real-ear gain were examined through theoretical models based on acoustic properties of the average human ear and ear simulator studies. The results of these investigations are used to demonstrate the effect of standing waves and eardrum impedance on probe measurements made in the ear canal. Investigations were also conducted in the sound field with a KEMAR manikin. A commercial probe microphone system was used to measure the SPL and real-ear gain at various locations with the KEMAR ear canal. The results emphasize the critical effect of probe location on absolute or relative ear canal measurements and indicate the necessity to establish clinical procedures for probe measurements based on relevant acoustic principles.

Acoustic Impedance Tests↗

PubMed1987

Effects of hearing loss on utilization of short-duration spectral cues in stop consonant recognition.

The purpose of this experiment was to evaluate the utilization of short-term spectral cues for recognition of initial plosive consonants (/b,d,g/) by normal-hearing and by hearing-impaired listeners differing in audiometric configuration. Recognition scores were obtained for these consonants paired with three vowels (/a,i,u/) while systematically reducing the duration (300 to 10 ms) of the synthetic consonant-vowel syllables. Results from 10 normal-hearing and 15 hearing-impaired listeners suggest that audiometric configuration interacts in a complex manner with the identification of short-duration stimuli. For consonants paired with the vowels /a/ and /u/, performance deteriorated as the slope of the audiometric configuration increased. The one exception to this result was a subject who had significantly elevated pure-tone thresholds relative to the other hearing-impaired subjects. Despite the changes in the shape of the onset spectral cues imposed by hearing loss, with increasing duration, consonant recognition in the /a/ and /u/ context for most hearing-impaired subjects eventually approached that of the normal-hearing listeners. In contrast, scores for consonants paired with /i/ were poor for a majority of hearing-impaired listeners for stimuli of all durations.

Aged↗

PubMed1987

Recognition of nonsense syllables by hearing-impaired listeners and by noise-masked normal hearers.

In the present study, speech-recognition performance was measured in four hearing-impaired subjects and twelve normal hearers. The normal hearers were divided into four groups of three subjects each. Speech-recognition testing for the normal hearers was accomplished in a background of spectrally shaped noise in which the noise was shaped to produce masked thresholds identical to the quiet thresholds of one of the hearing-impaired subjects. The question addressed in this study is whether normal hearers with a hearing loss simulated through a shaped masking noise demonstrate speech-recognition difficulties similar to those of listeners with actual hearing impairment. Regarding overall percent-correct scores, the results indicated that two of the four hearing-impaired subjects performed better than their corresponding subgroup of noise-masked normal hearers, whereas the other two impaired listeners performed like the noise-masked normal listeners. A gross analysis of the types of errors made suggested that subjects with actual and simulated losses frequently made different types of errors.

Adolescent↗

PubMed1986

Application of the Articulation Index and the Speech Transmission Index to the recognition of speech by normal-hearing and hearing-impaired listeners.

The present article is divided into four major sections dealing with the application of acoustical indices to the prediction of speech recognition performance. In the first section, two acoustical indices, the Articulation Index (AI) and the Speech Transmission Index (STI), are described. In the next section, the effectiveness of the AI and the STI in describing the performance of normal-hearing and hearing-impaired subjects listening to spectrally distorted (filtered) and temporarily distorted (reverberant) speech is examined retrospectively. In the third section, the results of a prospective investigation that examined the recognition of nonsense syllables under conditions of babble competition, filtering and reverberation are described. Finally, in the fourth section, the ability of the acoustical indices to describe the performance of 10 hearing-impaired listeners, 5 listening in quiet and 5 in babble, is examined. It is concluded that both the AI and the STI have significant shortcomings. A hybrid index, designated mSTI, which takes the best features from each procedure, is described and demonstrated to be the best alternative presently available.

Hearing Loss↗

PubMed1986

Log-linear modeling of consonant confusion data.

Log-linear models, in conjunction with the G2 statistic, were developed and applied to several existing sets of consonant confusion data. Significant interactions of consonant error patterns were found with signal-to-noise ratio (S/N), presentation level, vowel context, and low-pass and high-pass filtering. These variables also showed significant interactions with error patterns when categorized on the basis of feature classifications. Patterns of errors were significantly altered by S/N for place of articulation (front, middle, back), voicing, frication, and nasality. Low-pass filtering significantly affected error patterns when categorized by place of articulation, duration, or nasality; whereas, high-pass filtering only affected voicing and frication error patterns. This paper also demonstrates the utility of log-linear modeling techniques in applications to confusion matrix analysis: specific effects can be tested; variant cells in a matrix can be isolated with respect to a particular model of interest; diagonal cells can be eliminated from the analysis; and the matrix can be collapsed across levels of variables, with no violation of independence. Finally, log-linear techniques are suggested for development of parsimonious and predictive models of speech perception.

Humans↗

PubMed1986

Acoustics of ear canal measurement of eardrum SPL in simulators.

The effect of standing waves on the ear canal measurement of eardrum sound pressure level (SPL) was determined by both calculation and measurement. Transmission line calculations of the standing wave were made using the dimensions of the ANSI S3.25-1979 ear simulator and three different eardrum impedances. Standing wave curves have been obtained for the standard eardrum impedance at 1-kHz intervals in the range of 1-8 kHz. The changes in standing wave position due to each of the three eardrum impedances and their effects on ear canal measurements of SPL were computed for each of the eardrum impedances. Ear canal SPL measurements conducted on simulators modified to correspond to the eardrum impedances used in the calculations were compared to the computed values. Differences between eardrum SPLs and those measured at different locations in the ear canal approached a standing wave ratio (SWR) of 10-12 dB as the position of the measuring probe approached the standing wave minimum at each frequency. These maximum differences compared favorably with data developed by other investigators from real ears. Differences due to the eardrum impedance were found to be significant only in the frequency region of 2-5 kHz. Calibration of probes in a standard or modified ANSI simulator at the same distance from the eardrum as in the real ear reduces the eardrum SPL measurement errors to those resulting from differences in eardrum impedance.

Acoustic Stimulation↗

PubMed1986

Articulation index predictions of contextually dependent words.

Three investigations were conducted to determine the application of the articulation index (AI) to the prediction of speech performance of hearing-impaired subjects as well as of normal-hearing listeners. Speech performance was measured in quiet and in the presence of two interfering signals for items from the Speech Perception in Noise test in which target words are either highly predictable from contextual cues in the sentence or essentially contextually neutral. As expected, transfer functions relating the AI to speech performance were different depending on the type of contextual speech material. The AI transfer function for probability-high items rises steeply, much as for sentence materials, while the function for probability-low items rises more slowly, as for monosyllabic words. Different transfer functions were also found for tests conducted in quiet or white noise rather than in a babble background. A majority of the AI predictions for ten individuals with moderate sensorineural loss fell within +/- 2 standard deviations of normal listener performance for both quiet and babble conditions.

Adolescent↗

PubMed1985

Speech recognition and the Articulation Index for normal and hearing-impaired listeners.

The purpose of this experiment was to determine the applicability of the Articulation Index (AI) model for characterizing the speech recognition performance of listeners with mild-to-moderate hearing loss. Performance-intensity functions were obtained from five normal-hearing listeners and 11 hearing-impaired listeners using a closed-set nonsense syllable test for two frequency responses (uniform and high-frequency emphasis). For each listener, the fitting constant Q of the nonlinear transfer function relating AI and speech recognition was estimated. Results indicated that the function mapping AI onto performance was approximately the same for normal and hearing-impaired listeners with mild-to-moderate hearing loss and high speech recognition scores. For a hearing-impaired listener with poor speech recognition ability, the AI procedure was a poor predictor of performance. The AI procedure as presently used is inadequate for predicting performance of individuals with reduced speech recognition ability and should be used conservatively in applications predicting optimal or acceptable frequency response characteristics for hearing-aid amplification systems.

Adult↗

PubMed1984

Effects of age and mild hearing loss on speech recognition in noise.

Using an adaptive strategy, the effects of mild sensorineural hearing loss and adult listeners' chronological age on speech recognition in babble were evaluated. The signal-to-babble ratio required to achieve 50% recognition was measured for three speech materials presented at soft to loud conversational speech levels. Four groups of subjects were tested: (1) normal-hearing listeners less than 44 years of age, (2) subjects less than 44 years old with mild sensorineural hearing loss and excellent speech recognition in quiet, (3) normal-hearing listeners greater than 65 with normal hearing, and (4) subjects greater than 65 years old with mild hearing loss and excellent performance in quiet. Groups 1 and 3, and groups 2 and 4 were matched on the basis of pure-tone thresholds, and thresholds for each of the three speech materials presented in quiet. In addition, groups 1 and 2 were similar in terms of mean age and age range, as were groups 3 and 4. Differences in performance in noise as a function of age were observed for both normal-hearing and hearing-impaired listeners despite equivalent performance in quiet. Subjects with mild hearing loss performed significantly worse than their normal-hearing counterparts. These results and their implications are discussed.

Adult↗

PubMed1984

A probe earmold system for measuring eardrum SPL under hearing-aid conditions.

A miniature probe-microphone assembly for use with earmolds was developed to measure the sound pressure level (SPL) of a signal at the eardrum under hearing-aid conditions. The probe-earmold (PE) system was designed with the earmold as an integral part of the acoustic measurement system so that no part of the probe itself projects into the ear canal. Data obtained during a previous investigation with an ear simulator indicated that the PE system could be used to measure eardrum SPL accurately (+/- 3 dB) up to 6.0 kHz. In the current investigation, a behavioral experiment was conducted to validate the accuracy of the PE system on human ears. Comparisons were made between pure-tone thresholds obtained with a conventional earphone and those measured by the PE system using a hearing-aid receiver into an earmold-occluded ear. The basis for the study was the premise that the estimates of the eardrum SPL obtained from pure-tone thresholds are equivalent when the thresholds are determined by sound generated by an earphone into an unobstructed ear or by a hearing aid receiver into an earmold-occluded ear. Results of the study showed no statistically significant differences between the thresholds as determined by the two procedures confirming the simulator data. These results on human ears, together with the physical measurements in a simulator, suggest that the PE system can be used to measure eardrum SPL up to 6.0 kHz in an occluded ear.

Acoustic Impedance Tests↗

PubMed1983

Suggestions for optimizing reliability with the synthetic sentence identification test.

The reliability of the Synthetic Sentence Identification (SSI) test was determined for a group of 33 listeners with mild-to-moderate sensorineural hearing loss. Randomizations of the 10-item test were administered 12 times (six trials on each of two days) under identical listening conditions. Lists were presented monaurally, under earphones, at 90 dB SPL with a cafeteria background noise set at a signal-to-noise ratio (S/N) estimated (by adaptive procedure for each subject) to obtain 50% performance. Average scores ranged from 48.8% for Trial 1 to 67.9% for Trial 9. Reliability of the 12 measurements was determined by Pearson correlation, analyses of variance, and by testing individual differences in scores against a theoretical statistical distribution. Results evidenced large intra-subject variability, especially for the initial trials conducted in each testing session. However, if sufficient practice trials are presented each day under relatively difficult listening conditions, the scores on subsequent lists tend to remain relatively stable. Suggested procedures to optimize reliability are included.

Adolescent↗