Biomedical subjects

D D Dirks

Publications and source records attributed to D D Dirks.

At least 37 records · Page 2Linked to original sources

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↗

PubMed1983

Accuracy of adaptive procedure estimates of PF-max level.

A measure of maximum speech recognition ability (PB max) is often obtained in the clinical audiologic evaluation of patients. However, without developing a complete performance-intensity function (PIF), it is often difficult to determine an appropriate intensity level for measuring PB max. Levitt (1978) has described an adaptive procedure designed to estimate an intensity level at which maximum speech recognition performance could be measured. We have investigated the accuracy of this procedure by comparing speech recognition performance on a CNC word list presented at the level estimated by the adaptive procedure with maximum performance as measured on the listener's performance-intensity function. Using the presentation level indicated by the adaptive procedure, PB max scores were obtained for 12 of 16 normally hearing subjects and 19 of 25 listeners with mild-to-moderate sensorineural hearing loss. Similar accuracy was obtained for the hearing-impaired subjects using a single presentation level of 95 dB SPL, while use of a 40 dB SL speech level would have resulted in a lower proportion of PB-max measurements. Although PB max is most accurately estimated by delineating the entire performance-intensity function, the current results suggest that, if speech recognition is to be measured only at a single level, scores obtained at the level estimated by the adaptive procedure or at 95 dB SPL may serve as reasonable estimates of PB max for listeners with primarily cochlear hearing losses of less than or equal to 50 dB.

Adolescent↗

PubMed1982

A procedure for quantifying the effects of noise on speech recognition.

This paper describes the results of two experiments in which speech recognition performance was determined for listeners with sensorineural hearing loss, while listening in babble. Adaptive strategies were used in both experiments to measure the signal-to-babble ratio required to achieve a preselected level of performance at several speech presentation levels encountered in normal conversation or when listening through an amplification system. The results suggest that the proposed adaptive strategy may provide a practical method by which the relative effects of competition on speech recognition may be quantified in an individual listener.

Adolescent↗

PubMed1982

Evaluation of hearing-impaired listeners using a Nonsense-Syllable Test. I. Test reliability.

The reliability of a closed-set Nonsense-Syllable Test was determined on a group of 38 listeners with mold-to-moderate sensorineural hearing loss. Eight randomizations of the 91-item test (four trials on each of two days) were presented monaurally, under earphones, at 90 dB SPL with a cafeteria background noise set at a +20-dB S/N ratio. Performance under these conditions ranged from 21.4 to 91.2%, reflecting the wide range of syllable-recognition ability of these subjects. Reliability of the eight measurements was determined by analysis of variance and analysis of covariance structure (parallel-test modelling) for the entire test and each of 11 subtests. Overall and individual subject results failed to show any systematic differences in scores over eight trials. Likewise, no significant differences were found in performance on individual syllables, nor were changes in the relative occurrence of specific syllable confusions noted. The test is highly reliable when evaluating hearing-impaired subjects, and thus is appropriate for use in investigations where identical items are administered under multiple experimental conditions.

Adult↗

PubMed1982

Evaluation of hearing-impaired listeners using a Nonsense-syllable Test. II. Syllable recognition and consonant confusion patterns.

Syllable recognition ability and consonant confusion patterns were evaluated for 38 listeners with mild-to-moderate sensorineural hearing loss using the closed-set Nonsense-Syllable Test (NST). Performance for these materials varies as a function of consonant voicing, the position of the consonant in the syllable, and the accompanying vowel. Scores for listeners with steeply sloping audiometric configurations were consistently poorer than those for listeners with gradually sloping or flat audiograms. Consonant confusion analyses revealed place of articulation errors to be the most frequent, regardless of the listener's audiometric configuration. Analysis of consonant confusion patterns indicates the existence of a systematic relationship between consonant confusions and audiometric configuration. The NST findings are discussed in terms of the test's potential use and are compared to the results of existing confusion analyses.

Aged↗

PubMed1982

Some effects of spectral shaping on recognition of speech by hearing-impaired listeners.

The effects of spectral shaping on speech recognition were investigated for hearing-impaired listeners with flat and steep audiometric configuration. Three frequency responses were tested: uniform frequency gain, high pass filtering, and a response shaped relative to each subject's loudness discomfort level curve. Speech-recognition performance was measured at four levels (from 80 to 95 dB SPL) using nonsense syllable (NST) and synthetic sentence (SSI) tests, presented against a background of "cafeteria noise." No significant differences in performance on the NST were observed between the two subject groups across all spectral shapes (frequency response) and presentation levels. On the SSI, performance of subjects with flat audiometric configuration was highest using the uniform frequency response, while performance of listeners with steep configuration was poorest for the uniform response. The recognition data were compared with predictions of relative performance using a modification of the Articulation index (AI). The AIs provided accurate estimates of relative performance across spectral shapes but were not consistent with relative performance as a function of presentation level. The results indicate that the selection of spectral shape for optimal performance is influenced by the particular speech task used to test recognition and also suggest that, with further validation, the AI may provide an objective technique for selecting optimal spectral shape.

Aged↗

PubMed1981

The effect of occluded ear impedances on the eardrum SPL produced by hearing aids.

The purpose of the investigation was to determine the effect of eardrum and earmold impedance on eardrum sound pressure level (SPL) produced by a hearing aid receiver. Acoustic interactions between receivers and ears occurring at receiver resonances were explored and analyzed. Results with ear simulators showed that the effect of simulator eardrum impedance was increased in regions where ear and receiver impedance approached each other during resonances. Earmold acoustics were also significant factors at frequencies where their impedance were comparable to ear impedances. Resonant frequency shifts of 540 Hz in the region between 800 and 1500 Hz were observed for the range of simulator eardrum and earmold impedances employed, with SPL changes of 10 dB occurring at some frequencies. Results were different for each of the five receivers tested confirming the effect of the receiver characteristics on the eardrum SPL. A subsequent test was performed using real ears with results that agreed substantially with those obtained with the simulators.

Acoustics↗

PubMed1981

Speech recognition performance at loudness discomfort level.

The purpose of this experiment was to determine the relationship between the loudness discomfort level (LDL) and maximum speech recognition performance for listeners with sensorineural hearing loss. Performance-intensity functions were obtained for 30 listeners with mild to moderate sensorineural hearing impairment at five speech levels from -18 to +4 dB re: the LDL. Recognition scores were obtained for three speech materials. For all speech materials, recognition scores at levels below the LDL were equivalent to or higher than scores obtained at and above the LDL. These results support the contention that the LDL represents a sound pressure level above which no improvement in speech recognition occurs, and thus, might reasonably be used as the appropriate level for the saturation sound pressure level of a hearing aid.

Amplifiers, Electronic↗

PubMed1980

Use of digitized speech materials in audiological research.

Computer methods, based on the theory and application of signal processing, combined with numerical methods for simulating mathematical processes, facilitate greater objectivity in most aspects of speech intelligibility testing, including specification of the stimuli, control of the tests, evaluation of the responses, corrective feedback, and automatic interpretation. This paper discusses several basic issues in digital signal processing, and also describes the application of computer-aided procedures for recording and delivery of speech materials for audiologic research. Examples of the use of computer procedures for manipulation of digitized stimuli demonstrate the increased efficiency and versatility of these procedures compared to more conventional tape recording methods. In addition, the use of digitized recordings allows more reliable specification of speech levels than conventional calibration methods involving observations of signal peaks on a VU-meter.

Audiology↗