Licensure of graduates of foreign medical schools.
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Educational Measurement↗
Biomedical subjects
R M Cox
Publications and source records attributed to R M Cox.
Demonstration of binaural advantage in audiometric test rooms.
Binaural advantage was measured for 12 normally hearing subjects in a typical rectangular audiometric test room with a loudspeaker located in each corner. Four different loudspeaker configurations for presentation of signal and competition were evaluated. The results indicated that a configuration in which uncorrelated competition was delivered from both sides of the subject while the signal was presented from a 0 degree azimuth was the most resistant to interaural asymmetries resulting from the room geometry and produced the most consistent binaural advantages. Binaural advantage was then measured using this loudspeaker configuration for 15 hearing-impaired individuals wearing hearing aids. Although the group results indicate a mean unaided binaural advantage only slightly smaller than seen in the normal hearers, when hearing aids were worn an interaural asymmetry in a signal-to-competition ratio developed that reduced the clinical usefulness of the data for individuals. This outcome emphasizes that a valid clinical demonstration of binaural advantage is critically dependent on interaural symmetry in signal-to-competition ratios for both aided and unaided tests. Such symmetry may be difficult to achieve in a typical audiometric test room.
Adult↗
Combined effects of earmold vents and suboscillatory feedback on hearing aid frequency response.
The effect of setting the gain control of a hearing aid to a position just lower than that required to produce audible oscillation was investigated in the condition where the main feedback pathway was an earmold vent of either diagonal (side-branch) or parallel configuration. Results indicated that, with this gain control setting, suboscillatory feedback effects were superimposed on the filtering effect of the earmold vent. The outcome was the formation of spurious peaks in the frequency response of the hearing aid. Most of the data were collected using a KEMAR manikin and the effects were confirmed by measurements made in real ear canals. It is recommended that this gain control setting be avoided in hearing aid fitting.
Acoustics↗
Prediction of aided preferred listening levels for hearing aid gain prescription.
Relative accuracy was assessed for two methods for predicting preferred listening levels as estimated by measurements of the upper limit of the comfortable loudness range (ULCL). Sixteen hearing-impaired subjects provided ULCL data for eight test stimuli on each of five occasions. The stimuli were four narrow bands of noise centered at 500, 1000, 2000, and 4000 Hz and four narrow bands of speech babble also centered at 500, 1000, 2000, and 4000 Hz. Best estimates of ULCL were determined to be the means of the five measurements for each subject for each of the eight test signals. Results revealed that the mean ULCL for each speech-band stimulus was predicted more accurately from that subject's first measurement of ULCL for that speech-band than from his/her threshold for the same signal. However, the accuracy with which noise-band ULCLs could be used to predict the mean speech-band ULCL varied with frequency and with the number of trials averaged. Relationship of ULCL to preferred listening levels was explored by comparing results obtained in this study with work of previous investigators. Implications of the results for hearing aid gain prescription are discussed.
Acoustic Stimulation↗
Acoustic versus electronic modifications of hearing aid low-frequency output.
The rated quality and intelligibility of speech processed by hearing aids in which the low-frequency output had been reduced by either electronic modification (low-cut tone controls) or acoustic modification (vented or open earmolds) was investigated. Fifteen subjects with high-frequency hearing loss provided data for nine commercial hearing aids and both high and low background noise levels. Results for both background noise levels indicated that for hearing aids with a low-frequency cut off at or above 750 Hz (as measured in this investigation), the use of a vented or open earmold significantly improved both quality and intelligibility even when it had essentially no effect on the hearing aid's low-frequency output. The implication of the outcome is that for an individual with essentially normal low-frequency sensitivity and a high-frequency hearing loss, an earmold incorporating an opening should be used whenever possible, even though it may not be used for the purpose of controlling low-frequency amplification.
Acoustics↗
Relationship between aided preferred listening level and long-term listening range.
The long-term listening range was defined as extending, at any frequency, from the threshold of audibility to the upper limit of the comfortable loudness range. The relationship between the aided preferred listening level and the long-term listening range was investigated by analyzing data obtained from 16 hearing impaired subjects. Results support a tentative conclusion that the aided preferred listening level is equal to the midpoint of the long-term listening range. Application of this relationship to the specification of frequency/gain function is discussed.
Adult↗
A structured approach to hearing aid selection.
Many different procedures have been suggested for use in hearing aid selection: the practicing audiologist must choose among them. A structured approach to the hearing aid selection process is most likely to result in an optimal choice for each patient. This paper describes one such approach to the process of hearing aid selection which attempts to customize the selection procedure to make maximum use of each individual patient's response capabilities. The approach is presented in generic form and one implementation is described in detail.
Decision Making↗
Earmold modification effect measured by coupler, threshold and probe techniques.
The validity of probe tube microphone measurements in providing data indicative of the magnitude of the change in subjects' threshold resulting from changes in earmold configuration was investigated. The relationship between these measures in the real ear canal and the changes observed in 2-cm3 and Zwislocki couplers under similar circumstances or earmold modification was also measured. Standard, vented and 'open' earmold conditions were utilized. Threshold and probe-tube measurements were made. Statistical evaluation revealed that these two techniques did not produce significantly different results except at 125--165 Hz, where noise masking may have been a factor influencing the threshold data. Neither coupler as used gave an accurate quantitative estimate of the in-use effects of vented earmolds or the open earmold configuration, but the Zwislocki coupler gave a better approximation than the 2-cm3 coupler.
Acoustic Stimulation↗
Hearing-aid-processed signals: a new approach.
A new protocol for obtaining and utilizing hearing-aid-processed signals in hearing aid research or hearing aid selection is described. Data are presented which illustrate the extent to which this procedure may be expected to result in a signal spectrum at the subject's eardrum which is the same as the spectrum the subject would have received if the hearing aid itself had been placed on his ear (a directly-aided situation). An earlier investigation by the authors indicated that the traditional protocol for the production and utilization of hearing-aid-processed signals results in substantial discrepancies between these two spectra. The data presented were obtained using the KEMAR as the subject with a Zwislocki coupler as the KEMAR's ear canal/eardrum. The discrepancy between directly-aided and hearing-aid-processed spectra was typically +/- 2 dB for ear-level hearing aids fitted using standard, vented, or open earmolds (in open earmold fittings only the amplified component of the directly-aided spectrum is reproduced).
Acoustic Stimulation↗
Expectations about hearing aids and their relationship to fitting outcome.
Clinicians are often concerned that unrealistic prefitting expectations can have a negative impact on fitting success for new, hearing aid wearers. To investigate this concern and to explore the potential value of measuring expectations, we developed the Expected Consequences of Hearing aid Ownership (ECHO) questionnaire as a companion to the Satisfaction with Amplification in Daily Life questionnaire. Four experiments were conducted to (1) determine realistic expectations for hearing aids, (2) evaluate expectations of new users, (3) measure reliability of prefitting expectations, and (4) assess relationships between prefitting expectations and postfitting satisfaction. Novice hearing aid users were found to have stable prefitting expectations about hearing aids, and these expectations were unrealistically high for the typical individual. There were many different expectation patterns across subjects. Of the four subscales of the ECHO, only one was predictive of the corresponding satisfaction data. Potential clinical applications are described.
Aged↗
Spectral changes produced by earphone-cushion reproduction of hearing aid-processed signals.
This investigation was conducted to assess the extent to which hearing aid-processed signals present an acoustic signal to the subject which has a frequency response equivalent to that which the hearing aid itself would have provided. The frequency response of a hearing aid receiver which was coupled directly to the ear canal ("aided" condition) was compared with the frequency response of the same receiver when its output was recorded on magnetic tape and then presented to the subject via a TDH-49 earphone ("pseudoaided" condition). Results indicated that when the earphone was mounted in an MX-41/AR cushion or either of two circumaural cushions, the spectrum of the sound arriving at the subject's eardrum in the pseudoaided condition was substantially different from the spectrum delivered in the aided condition.
Hearing Aids↗
Side branch and parallel vent effects in real ears and in acoustical and electrical models.
The purpose of the project was to demonstrate and explain the acoustic effects of side branch and parallel vents in individual real ears. It was shown that parallel and side branch vents produce similar low frequency filtering effects and vent-associated reactance resonances. However, when the input system incorporates a side branch vent the sound pressure produced in the ear canal at frequencies above the vent-associated resonance is less than that produced when the input system is unvented. This effect is not seen when the input system is associated with a parallel vent. Data obtained in the real ear canals were compared to analogous measurements made using an acoustical model (the Zwislocki coupler) and an electrical model designed to simulate the hearing aid receiver, input tubing, earmold, ear canal, and eardrum. Both models yielded data very similar to the real ear results. The advantages of each model in predicting the effects of individual earmold vents are discussed.
Ear Canal↗
Sound levels in a 2-cc cavity, a Zwislocki coupler, and occluded ear canals.
Probe-tube measurements of the differences in sound levels at three locations in ear canals were compared to the differences in levels measured at analogous positions in a Zwislocki coupler and a 2-cc cavity. The results support the recommendation of Sachs and Burkhard that probe tube measurements should not be made with the probe tube flush with the earmold tip and close to the sound inlet bore. In real ear canals the transfer functions to the eardrum presented by Bruel, Frederikson, and Rasmussen and by Studebaker agree well with each other but differ somewhat from the one used by Sachs and Burkhard. In agreement with Bruel et al., the data of this study reveal a plateau in the relationship between real ear and 2-cc cavity responses between about 1.6 and 4.0 kHz, the relative intensity level of which may depend upon residual ear canal volume.
Acoustics↗