Biomedical subjects

R M Cox

Publications and source records attributed to R M Cox.

At least 37 records · Page 2Linked to original sources

PubMed1994

Prediction of hearing aid benefit: the role of preferred listening levels.

The listening level chosen by a hearing aid wearer for receiving amplified speech in noise has a substantial impact on the benefit that the hearing aid can provide. Chosen listening levels determine (1) the extent to which audibility of speech cues is improved by amplification, (2) the in situ distortion generated by the hearing aid, and sometimes (3) the auditory resolution abilities available to the hearing-impaired listener. All of these variables have been shown to affect hearing aid benefit. Thus, to predict benefit in any particular listening environment, the listening level that the wearer would choose in that setting must be known with some precision. This paper reports two studies of chosen, or preferred, listening levels. We present evidence to show that preferred listening levels vary with changes in the listening environment, especially when the signal-to-noise ratio is favorable. We describe a method for predicting preferred listening level changes in some environments that differ in talker levels and/or signal-to-noise ratios.

Acoustic Stimulation↗

PubMed1994

Relationship between in-situ distortion and hearing aid benefit.

In-situ hearing aid distortion is defined as distortion measured in the ear canal with stimulus inputs and hearing aid settings that are similar to those the hearing aid wearer will experience in daily life. This preliminary study examined possible relationships between in-situ distortion and benefit for appropriately fitted contemporary hearing aids. Simulated in-situ distortion was determined for 97 hearing aid fittings, divided among three typical listening environments: living room, classroom lecture, and social event. Measures included intermodulation, harmonic, and transient distortion. Overall results of between- and within-subject analyses of data suggested that there was a significant relationship between distortion and benefit in both reverberant and noisy environments similar to a classroom lecture and a social event, respectively. This outcome was seen despite the fact that distortion was quite low in absolute terms. Analyses also suggested that in-situ harmonic distortion was most closely related to benefit and that the other types of distortion measured did not make additional contributions to benefit prediction. We propose that measurements of in-situ harmonic distortion might be a valuable addition to hearing aid evaluations.

Aged↗

PubMed1993

Prediction of benefit from linear hearing aids in nonreverberant listening environments.

Hearing aid benefit, defined in terms of improved speech intelligibility, was measured for 16 elderly hearing-impaired subjects. Twelve conditions were tested, simulating a range of daily situations from typical home environments to moderate-sized social gatherings, and assuming a small talker-listener distance (thus maintaining essentially nonreverberant listening conditions). Each subject was fitted with the same type of programmable hearing aid. The goals were to develop a model for the prediction of benefit based on hearing loss, listening environment, and amplification variables, and to assess the potential accuracy of the model. Two models were developed using multiple linear regression analyses. The prefitting model used data that would be available before a hearing aid fitting, that is, audiogram and listening environment data. This model, although potentially useful as a counseling tool, was relatively inaccurate. Six of the 16 subjects yielded benefit data that were consistently different from the model's predictions. The postfitting model used information that could be obtained during a hearing aid fitting about audibility changes resulting from amplification. This model produced more accurate, but still imperfect predictions of benefit. Benefit obtained by three subjects deviated substantially from the predictions of the postfitting model. It was concluded that a model producing fairly accurate benefit predictions must encompass additional variables beyond those considered here. Nevertheless, these models may be useful for prediction of typical benefit for potential hearing aid wearers.

Acoustics↗

PubMed1993

Indices of frequency and temporal resolution as a function of level.

Several investigators have suggested that between-subject variations in hearing aid benefit may be related to between-subject variations in auditory resolution. Evaluation of this relationship is complicated by the need to assess resolution at several frequencies and levels in hearing-impaired listeners who may not tolerate lengthy test procedures. This paper reports data from normal-hearing listeners for abbreviated indices of frequency and temporal resolution. For a particular frequency-stimulus level combination, both indices may be derived from three pure-tone thresholds obtained with different masking stimuli. Norms are reported as a function of masker level for each index at four test frequencies. Changes in the indices as a function of masker level were consistent with expectations based on related studies by other investigators. Norms were obtained using a supra-aural earphone. Comparison of results from supra-aural and insert earphones suggested that low-frequency sound leakage substantially affected the norms for 500 Hz. Reliability of individual indices was good to excellent.

Acoustic Stimulation↗

PubMed1993

On the evaluation of a new generation of hearing aids.

Hearing aids with new technological features offer the promise of novel speech-processing and loudness-control capabilities. Full exploitation and assessment of these capabilities will call for the acceptance of fitting and evaluation strategies different from those currently used for traditional linear hearing aids. Until an appropriate set of procedures comes into relatively widespread use, it will be difficult to draw definitive conclusions about the desirability and effectiveness of the new options in amplification systems. This paper reviews some of the issues that should be considered as new evaluation procedures are explored.

Amplifiers, Electronic↗

PubMed1992

Evaluation of the speech intelligibility rating (SIR) test for hearing aid comparisons.

The SIR test was created for use in hearing aid comparisons. The test protocol obtains listener judgments of the intelligibility of connected speech passages. This study was conducted to evaluate the effectiveness of the SIR test in differentiating among hearing aids. Specific research questions were (a) Is the sensitivity of the SIR test sufficient for differentiating among very similar and slightly dissimilar hearing aids? (b) Does the SIR test result in reliable hearing aid rankings? and (c) What are the effects of using shortened connected speech passages? Ten listeners with hearing impairments rated the intelligibility of both full-length and shortened SIR test passages while wearing each of four individually selected hearing aids representing three different frequency/gain prescriptions. Results suggested that the SIR test is capable of differentiating among slightly dissimilar hearing aids and that hearing aid rankings resulting from speech intelligibility ratings were reliable. The decision to use full-length or shortened SIR test passages depends on the outcome the user wishes to maximize. Under the conditions used in this study, maximum sensitivity was achieved with ratings from five shortened passages, whereas maximum reliability was obtained with three full-length passages.

Adult↗

PubMed1992

Maturation of hearing aid benefit: objective and subjective measurements.

The goals of this investigation were to determine whether hearing aid benefit improved significantly over the first 10 weeks of hearing aid use and whether time-related changes in benefit (if any) were affected by the type of benefit measurement (i.e., objective or subjective). A total of 17 hearing-impaired subjects participated, with different subjects completing different phases of the study. Benefit was measured soon after the hearing aid fitting and again after 10 weeks of adjustment to hearing aid use. Objective benefit data were determined using the Connected Speech Test. No significant changes in objective benefit were noted in noisy or reverberant listening environments when visual cues were available. However, in a low-noise setting and in a noisy setting without visual cues, improvements in objective benefit were seen over time. Subjective benefit data were derived from responses to the Profile of Hearing Aid Benefit. These data indicated significant benefit improvement over time in all five types of daily life situations assessed, although the improvement was small in reverberant and noisy environments. Significant, but modest, correlations were found between objective and subjective data for low-noise and reverberant listening environments. Comparison of experienced and novice hearing aid wearers suggested that although experienced wearers obtain more benefit than novice wearers, they evidence similar time-related changes in benefit during the first 10 weeks of new hearing aid use.

Aged↗

PubMed1992

Predictability and reliability of hearing aid benefit measured using the PHAB.

This investigation explored the extent to which self-assessed hearing aid benefit measured by the Profile of Hearing Aid Benefit (PHAB) could be predicted from adaptation to hearing loss and/or from communication difficulties reported without amplification. Adaptation to hearing loss was measured using 13 scales of the Communication Profile for the Hearing Impaired (CPHI). These were combined to produce three composite CPHI scores. Results from 58 experienced hearing aid wearers indicated that benefit was significantly related to magnitude of unaided difficulties for all seven PHAB subscales. In addition, one of the three composite CPHI scores contributed to benefit prediction for the two sound perception subscales of the PHAB. Test-retest reliability of PHAB subscale scores was evaluated for 28 subjects using correlations and difference distributions. Reliability was found to be consistent with previous studies but modest. Critical differences were large compared with the anticipated size of benefit differences due to, for example, different hearing aid prescriptions. It is concluded that the PHAB is best suited for group research: when used for individual subjects, the PHAB may not be sensitive enough to detect important differences between hearing aid conditions.

Adaptation, Psychological↗

PubMed1991

Comparison of objective and subjective measures of speech intelligibility in elderly hearing-impaired listeners.

Three experiments were performed to evaluate the use of subjective intelligibility estimations as a method for measuring hearing aid benefit. Subjective and objective speech intelligibility scores were compared for young normal-hearing and elderly hearing-impaired listeners. Objective intelligibility scores were obtained using the Connected Speech Test (CST). This test consists of conversationally produced passages of speech that the listener repeats sentence by sentence. To provide subjective intelligibility scores, listeners estimated the percentage that they understood of each CST passage. Comparison of the two types of scores revealed that they were closely related in both groups of subjects (r = .82-.92). Although the two types of scores were essentially equal for normal-hearing subjects, the hearing-impaired listeners tended to produce subjective estimations of intelligibility that were significantly lower than their objective scores. Manipulation of visual cues and amplification, in an attempt to influence the hearing-impaired listeners' expectation of understanding speech, had no effect on the subjective-objective score differential. The difference between subjective and objective scores in the hearing-impaired group was not related to audiometric variables such as speech reception threshold, audiogram, or duration of hearing loss. It was concluded that comparative hearing aid evaluations using subjective intelligibility estimates would usually produce the same relative outcome as evaluations using the objective intelligibility measurement procedure. However, scores obtained with the objective procedure had smaller critical differences. Thus, when both types of scores are based on the same number of passages, the objective measurement procedure would be the more sensitive to differences among hearing aids.

Adolescent↗

PubMed1991

Preferred hearing aid gain in everyday environments.

Thirty-three hearing-impaired individuals were each fitted with three hearing aids. The instruments conformed to three frequency-gain prescriptions, differing by a total of 8 dB/octave, with the middle prescription derived using the MSU version 3.0 procedure. The subjects were divided into three matched groups of eleven. Each group used the fitted hearing aids in one of three everyday listening environments representing quiet, reverberant, and noisy situations, respectively. In each listening environment, preferred hearing aid gain for conversationally produced speech was measured in each hearing aid condition for each subject. Preferred gain in daily listening situations was compared to prescribed gain. Results indicated that: (1) preferred gain averaged across all three environments was about equal to prescribed gain, (2) mean preferred gain in each separate environment was substantially different from the prescribed level, (3) volume control adjustments of about +/- 8 dB relative to the prescribed level would be necessary to accommodate the preferred gain settings of the typical hearing aid wearer in daily life. Guidelines are presented for establishing recommended volume control settings for hearing aid users who may be unable to set the volume control independently.

Acoustics↗

PubMed1991

Hearing aid benefit in everyday environments.

Hearing aid benefit was measured for three matched groups of eleven hearing-impaired subjects, each serving in one typical listening environment. Benefit was quantified in terms of improvement in intelligibility score for the Connected Speech Test. Each subject was individually fitted with three hearing aids, differing in nominal frequency response slope by a total of 8 dB/octave. Research questions centered on the amount of benefit typically realized in everyday environments and the interactions of this benefit with frequency response and/or visual cues. Results revealed: (1) mean benefit in a living-room type setting was about 24% and significantly greater than in a reverberant setting (7%) and a noisy setting (-1%); (2) despite the relatively large mean difference in benefit between the reverberant and noisy environments, the difference was not statistically significant (p greater than 0.05); (3) the addition of visual cues did not change hearing aid benefit in any tested environment; (4) there was no significant overall trend for any of the three different frequency-response slopes to give superior benefit in any environment; (5) 76% of the subjects achieved significantly different benefit (p less than 0.05) in at least one hearing aid condition when data were considered on an individual basis; and (6) articulation indices in the aided conditions did not successfully predict the observed within-subject benefit differences. Benefit was significantly related to speech reception threshold in the living-room environment. However, in the less favorable environments, benefit and hearing loss were not related despite the fact that benefit varied considerably across subjects.

Acoustics↗

PubMed1991

Comparison of two questionnaires for patient-assessed hearing aid benefit.

Two questionnaires, the Profile of Hearing Aid Benefit (PHAB) and the intelligibility Rating Improvement Scale (IRIS), were developed to measure self-assessed hearing aid benefit. The response format differed in the two instruments: the PHAB required estimation of the proportion of time that certain situations presented communication problems, whereas the IRIS required estimation of the percentage of speech that could be understood in the same situations. The purpose of the study was to evaluate the potential of each questionnaire for clinical and research applications. They were compared in terms of the amount of self-assessed benefit they produced and their sensitivity to benefit differences in different listening situations. Both questionnaires were completed by 42 hearing aid wearers. Analyses of the results indicated that (1) the PHAB produced a significantly lower overall estimate of hearing aid benefit than the IRIS; (2) the PHAB was more sensitive than the IRIS to benefit differences in different listening situations; and (3) the pattern of self-assessed benefit determined with the PHAB was in agreement with previous investigations, whereas the pattern derived from the IRIS scores was not.

Adult↗

PubMed1990

Development of the Profile of Hearing Aid Performance (PHAP).

This paper reports the development of the Profile of Hearing Aid Performance (PHAP), a 66-item self-administered inventory that quantifies performance with a hearing aid in everyday life using both seven-score and four-score profiles. The profiles assess experience with amplification in terms of speech communication in three types of listening situations and in terms of reactions to amplified environmental sounds. The PHAP has been evaluated using groups consisting mainly of elderly hearing aid wearers having mild to moderate hearing impairments. Internal consistency reliability of the scales and subscales ranges from .70 to .91. Test-retest correlations range from .66 to .88. Ninety percent and 95% critical differences are presented to facilitate evaluation of differences between scores for the same individual under different conditions. It is envisioned that the PHAP will have its principal application in research evaluating and comparing different approaches to hearing aid fittings. In addition, the inventory can be used clinically to assess existing hearing aid fittings.

Activities of Daily Living↗

PubMed1990

Evaluation of an in-situ output probe-microphone method for hearing aid fitting verification.

Several hearing aid prescription procedures specify frequency gain functions in terms of the desired levels of amplified speech. The most direct method for verifying hearing aid fittings based on these procedures requires a measurement of amplified speech in the ear canal. This paper describes the evaluation of a probe microphone measurement procedure designed to measure amplified speech to verify hearing aid fittings using the MSUv3 prescription procedure. With minor modifications, the same protocol could be used with other prescriptive procedures. Hearing aids were fitted to a group of subjects with sensorineural hearing impairment. Data derived from the fittings were analyzed to assess several issues relating to the procedure itself and to prescriptive fittings in general. The main results were: (1) with over the ear hearing aids, most prescriptions can be matched with an RMS error of 5 dB or less through the frequency range from 500 to 2500 Hz; (2) even though actual fittings usually do not perfectly correspond with their prescriptions, differences among frequency gain prescriptions are preserved in hearing aid fittings if the RMS error of the fitting is 5 dB or less; (3) if sound field stimuli presented to the hearing aid are precisely controlled, an in situ output verification method produces valid results; (4) when hearing aids are fitted with gain similar to that prescribed by the MSUv3 procedure, the maximum comfortable speech input level is typically about 72 dB; (5) the SSPL90 prescription generated by the MSUv3 procedure overestimates desired SSPL90 by 7 dB on average.

Audiometry↗

PubMed1989

Development of the Speech Intelligibility Rating (SIR) test for hearing aid comparisons.

The Speech Intelligibility Rating (SIR) Test has been developed for use in clinical comparisons of hearing aid conditions. After listening to a short passage of connected speech, subjects generate a rating proportional to its intelligibility using an equal-appearing interval scale from 0 to 10. Before test passages are presented, the signal-to-babble ratio (SBR) is adjusted to a level that elicits intelligibility ratings of 7-8 for a "setup" passage. Then, with SBR held constant, three or more test passages are rated and the results averaged for each aided condition. This paper describes the generation of recorded test materials and their investigation using normally hearing listeners. Based on these data, a critical difference of about 2 scale intervals is recommended. A future paper will deal with results for hearing-impaired subjects.

Hearing Aids↗

PubMed1989

The Connected Speech Test version 3: audiovisual administration.

The Connected Speech Test (CST) is used to measure the intelligibility of everyday speech; it is intended primarily for quantifying hearing aid benefit. The test consists of 48 passages of conversationally produced connected speech, each passage concerning a familiar topic and comprising 10 sentences. Listeners are apprised of the passage topic in advance and are required to repeat the sentences one at a time. Each passage contains 25 scoring words. The test is recorded audiovisually. In previous papers, we have reported the development of the test materials and investigations of the use of the audio portion with normally hearing and hearing-impaired listeners. Audio versions of the test have been developed for use with normal hearers (CST version 1), and for hearing-impaired listeners (CST version 2). In the present paper, we report a study of the test administered audiovisually. Twenty-six normally hearing subjects responded to audiovisual presentation of all 48 test passages. On the basis of the results, a new version of the test (CST version 3) was generated. In this new version, the test passages are presented in designated sets of four or six passages. The critical difference between two scores is estimated to be the same for both audio and audiovisual administration.

Adult↗

PubMed1989

Comfortable loudness level: stimulus effects, long-term reliability, and predictability.

This paper reports the results of a series of investigations of comfortable loudness levels with particular reference to their application to hearing aid gain prescriptions. Experiment 1 studied the effects of several stimulus waveforms, bandwidths, and durations on comfortable loudness levels for normal and hearing impaired listeners. Speech band comfort levels were found to be significantly higher than equal-duration noise band or warble tone comfort levels. Comfortable loudness levels were found to be independent of warble tone modulation parameters and of stimulus bandwidth (stimuli did not exceed critical bandwidths). In Experiment 2, reliability of comfortable loudness levels was evaluated in hearing-impaired subjects over two consecutive 1-year periods. Results indicated that comfortable loudness levels were slightly less reliable than thresholds. In addition, the results were consistent with a hypothesis that exposure to amplified sound produces a small increase in comfortable loudness levels. In Experiment 3, data from 67 hearing-impaired subjects were used to develop regression equations for prediction of comfortable loudness levels. Thresholds at the test frequencies were combined with comfortable loudness data at 500 Hz and 4,000 Hz. The prediction method was then evaluated using a new group of 25 subjects. Accuracy of predictions of comfort levels was substantially better with the new method than with an older method that relied exclusively on threshold data. Relevance of the outcomes to hearing aid fitting procedures is discussed.

Adult↗

PubMed1988

Composite speech spectrum for hearing and gain prescriptions.

Average long-term RMS 1/3-octave band speech spectra were generated for 30 male and 30 female talkers. The two spectra were significantly different in both low and high frequency bands but were similar in the mid-frequency region. It was concluded that a single spectrum could validly be used to represent both male and female speech in the frequency region important for hearing aid gain prescriptions: 250 Hz through 6300 Hz. In addition, the male and female spectra were compared with analogous spectra reported by Byrne (1977) and Pearsons, Bennett, and Fidell (1977). For each sex, significant differences were found among the three spectra in a few frequency bands. The best estimate of the average speech spectrum for each sex was obtained from a weighted average of the three sets of data, excluding the significantly different data points. The long-term RMS 1/3-octave band speech spectrum for male and female talkers combined was derived for use in hearing aid gain prescriptions.

Adult↗