Björn Hagerman

Efficient Adaptive Methods for Measuring Speech Reception Threshold in Quiet and in Noise

An adaptive method for measuring speech reception threshold in noise (S/N-threshold) was evaluated with regard to reliability and learning effect. A corresponding method was also tested for speech reception threshold in quiet (SRT). The methods are designed for use with a speech and noise material developed by Hagerman (1982a). Ten normal-hearing subjects and 40 hearing-impaired subjects were tested, the results showing that the test-retest reliability of the S/N-threshold was much better with the new, adaptive, method than with the old one, which was not adaptive. With the new method, a S/N-threshold can be measured within two minutes for most patients (after the initial short training) with a reliability, i.e. standard deviation, of 0.78 dB and a learning effect that is negligible for most subjects if one training list is presented before the test session. It was also concluded that the adaptive method designed for the sentences in quiet gives at least as reliable an SRT result as the old spondée method (including learning effects), but in a shorter time.

Clinical Measurements of Speech Reception Threshold in Noise

New lists of spoken sentences, edited in a computer, word by word, were tested clinically together with a noise, spectrally shaped as the speech. The purpose was to investigate the reliability and the learning effect of the speech reception threshold in noise, and also to assess the relations of this threshold to conventional audiometric measures. The threshold values ranged from -7 to +7 dB signal-to-noise ratio for the 97 ears investigated. Reliability, expressed as standard deviation for repeated measurements, deteriorated from 0.7 to 1.1 dB as the threshold deteriorated. Learning effect between the first and the second threshold increased from 0 to 1 dB as the threshold deteriorated. No conventional audiometric test showed a high correlation to this threshold measure. The discrimination of the sentences without noise as well as the self-rated speech recognition in noise were also investigated.

Perceived sound quality of reproductions with different frequency responses and sound levels

Three programs (female voice, jazz music, and pink noise) were reproduced using four different frequency responses and two different sound levels. Fourteen normal hearing subjects listened to the reproduction via earphones and judged the sound quality on seven perceptual scales (loudness, clarity, fullness, spaciousness, brightness, softness/gentleness, and nearness) and a fidelity scale. Significant differences among the reproductions appeared in all scales and could be attributed to the differences in frequency response or sound level or both. Interactions between the reproductions and the programs could be explained by the relations between the spectrum of the programs and the frequency responses used. The results for the noise program were similar to those for the jazz music program.

The efficacy of N-acetylcysteine to protect the human cochlea from subclinical hearing loss caused by impulse noise: A controlled trial

In military outdoor shooting training, with safety measures enforced, the risk of a permanent, noise-induced hearing loss is very small. But urban warfare training performed indoors, with reflections from walls, might increase the risk. A question is whether antioxidants can reduce the negative effects of noise on human hearing as it does on research animals. Hearing tests were performed on a control group of 23 military officers before and after a shooting session in a bunker-like room. The experiments were repeated on another group of 11 officers with peroral adminstration of N-acetyl-cysteine (NAC), directly after the shooting. The measurements performed were tone thresholds; transient-evoked otoacoustic emissions, with and without contralateral noise; and psycho-acoustical modulation transfer function (PMTF), thresholds for brief tones in modulated noise. Effects from shooting on hearing thresholds were small, but threshold behavior supports use of NAC treatment. On the PMTF, shooting without NAC gave strong effects. Those effects were like those from continuous noise, which means that strict safety measures should be enforced. The most striking finding was that the non-linearity of the cochlea, that was strongly reduced in the group without NAC, as manifested by the PMTF-results, was practically unchanged in the NAC-group throughout the study. NAC treatment directly after shooting in a bunkerlike room seems to give some protection of the cochlea.

Speech recognition threshold in slightly and fully modulated noise for hearing-impaired subjects

A previously developed speech test with sentences in noise was modified in an attempt to increase its efficiency. Thus the original, slightly modulated (SM) noise was changed to be fully modulated (FUM), and the speech-to-noise ratio of each word was controlled to make all the words equally difficult. The new and the old version were compared in 41 hearing-impaired subjects. The learning effect was similar for both noises, but the variability was higher for the FUM noise. However, the efficiency of the speech test was slightly better for the FUM noise. Speech recognition in both types of noise was correlated with pure-tone thresholds at high frequencies, i.e. 2000 Hz and above, but not to tone thresholds at lower frequencies. Results in FUM noise and in SM noise were highly correlated, with a correlation coefficient of 0.86. Sumario Se modificó una prueba de frases en ruido previamente desarrollada con la intención de incrementar su eficiencia. A diferencia de la original, los sonidos levemente modulados (SM) fueron cambiados para que tuvieran modulación total (FUM), y la tasa de relación lenguaje/ruido de cada palabra se controló para que todas las palabras tuvieran el mismo nivel de dificultad. Se comparó la nueva y la vieja versión de la prueba en un grupo de 41 sujetos hipoacúsicos. El efecto de aprendizaje fue el mismo para ambos ruidos, pero la variabilidad fue mayor para el ruido FUM. Sin embargo, la eficiencia de la prueba de lenguaje fue levemente mejor para el ruido FUM. El reconocimiento del lenguaje en medio de ambos tipos de ruidos se correlacionó con los umbrales tonales puros a altas frecuencias, p.ej., 2000 Hz y por encima, pero no para umbrales tonales en bajas frecuencias. Los resultados con ruido FUM y con ruido SM correlacionaron fuertemente, con un coeficiente de correlación de 0.86.

Questionnaires on Desirable Properties of Hearing Aids

Three questionnaires were presented to 49 hearing-impaired patients. They were asked to rank different properties of behind-the-ear hearing aids with regard to their importance. The first questionnaire dealt with physical properties such as size, weight, and battery-cost, but also with the importance of good sound quality. The second questionnaire focused on the relative importance of various sound quality dimensions, such as softness, clarity, fullness, and others. The third questionnaire asked for suitable sound programs to be used in the procedure of hearing aid fitting in the clinic. Sound quality scored the highest rank by 43 of the patients, and clarity was considered to be the most important sound quality dimension. The most preferred sound programs included male and female voices with or without a background of other voices.

Successful and unsuccessful users of bilateral amplification: Differences and similarities in binaural performance

Abstract Bilateral amplification seems to be the best solution for bilaterally hearing-impaired persons. Nevertheless, some individuals are unsuccessful with this strategy. The goals of the present study were to develop tests to improve the diagnostic test battery before rehabilitation of hearing-impaired persons with bilateral or unilateral amplification, and to evaluate the tests with normally-hearing subjects and with two groups of hearing-impaired persons. The latter two groups contained 11 successful and 11 unsuccessful users of bilateral amplification respectively. Hearing thresholds, speech recognition in noise, signal analysis ability, binaural abilities, and dichotic tests were used in the investigation. The subjects answered a questionnaire and hearing aid gain curves were measured. The results for the two groups were similar for peripheral hearing functions and binaural performance. The unilateral amplification group showed significantly worse results in speech-in-noise and dichotic tests. Spatial aspects within the questionnaire were correlated to amplification preference. We therefore suggest the inclusion of speech-in-noise, dichotic tests, and questions on spatial orientation into the diagnostic scheme before rehabilitation with hearing aids. Sumario La amplificación bilateral parece ser la mejor solución para las personas con daño auditivo bilateral. Sin embargo, algunos individuos no tienen éxito con esta estrategia. Las metas del presente estudio fueron desarrollar pruebas para mejorar la batería diagnósticas de exámenes antes de la rehabilitación de personas hipoacúsicas con amplificación unilateral o bilateral, y evaluar las pruebas en personas con audición normal, y con dos grupos de personas con daño auditivo. Los últimos dos grupos incluían 11 usuarios exitosos y 11 usuarios no exitosos de amplificación bilateral, respectivamente. Se utilizaron en esta investigación umbrales auditivos, reconocimiento de lenguaje en ruido, capacidad de análisis de la señal, capacidades binaurales y pruebas dicóticas. Los sujetos contestaron un cuestionario y se midieron las curvas de ganancia para auxiliares auditivos. Los resultados para los dos grupos fueron similares para las funciones auditivas periféricas y para el desempeño binaural. El grupo de amplificación unilateral mostró resultados significativamente peores en las pruebas dicóticas y de lenguaje en ruido. Los aspectos espaciales dentro del cuestionario se correlacionaron con las preferencias en la amplificación. Sugerimos, por tanto, la inclusión de pruebas dicóticas, de lenguaje en ruido y preguntas sobre orientación espacial en el esquema diagnóstico antes de la rehabilitación con auxiliares auditivos.

Efficiency of speech audiometry and other tests

A formula for expressing the efficiency of audiological tests is proposed: E = (vb/vw - 1)/T where vb is the variance between subjects, vw is the variance within subjects and T is the testing time. This makes it possible to compare various tests even if they require different testing times. The formula has been used on various speech tests and on pure-tone thresholds for a specific group of hearing-impaired subjects, showing that pure-tone threshold tests are much more efficient than speech tests. Some suggestions are given on how to make speech tests in noise more efficient. It is concluded that the proposed formula of test efficiency should be considered when new tests are designed in order to get quick tests which add as much information as possible.

Perceived sound quality in a hearing aid with vented and closed earmould equalized in frequency response.

Nine normal-hearing subjects listened to speech and music in a hearing aid, either through a vented earmould or a closed earmould. The complex frequency responses of the two systems were made equal by compensating the aid and closed mould combination with a digital filter. The subjects rated the perceived sound quality of the systems on seven perceptual scales and a scale for overall impression. The results of the ratings support the hypothesis that there is no difference in perceived sound quality between vented and closed earmoulds that are equalized in frequency response, provided that the perceived loudness is the same in both cases.

The effect of presentation level and compression characteristics on sentence recognition in modulated noise

The effect of fast-acting compression on speech recognitionin fully modulated (FUM) noise in listeners with normaland impaired hearing was investigated in two experiments. We wanted to determine the relationships between the benefitfrom compression and some audiological factors.Furthermore, the sensitivity to changes in compressionparameters was also evaluated. The results showed thattwo-thirds of the listeners performed worse with fast-actingcompression than with linear processing. Normal-hearinglisteners showed the most benefit from compression. A significantrelationship was found between benefit from compressionand speech-to-noise ratio at threshold (SNRT) inslightly modulated (SM) noise. Pure-tone threshold wasfound to be a weak predictor of benefit from compression.No relationship was found between benefit from compressionand the release of masking for the FUM noise. Thevariability in the results across different compressionparameters was related to SNRT in SM noise. The resultssuggest an inverse relationship between benefit from compressionand the severity of the suprathreshold hearing loss. Sumario Se investigó en dos experimentos el efecto de una compresiónde acción rápida sobre el reconocimiento dellenguaje con ruido totalmente modulado (FUM), ensujetos con una audición normal o alterada. Quisimosdeterminar la relación entre el beneficio de la compresióny algunos otros factores audiológicos. Más aún, se evaluóla sensibilidad a los cambios en los parámetros de compresión.Los resultados mostraron que dos tercios de lossujetos mostraron un beneficio negativo de la compresión.Los sujetos normo-oyentes mostraron el mayorbeneficio de la compresión. Se encontró una relación significativaentre el beneficio de la comprensión y larelación señal/ruido a nivel del umbral (SNRT), conruido levemente modulados (SM). Se encontró que elumbral tonal puro fue un débil pronosticador del benefi-cio de la compresión. No se halló relación entre el benefi-cio de la compresión y la liberación del enmascaramientopara el ruido FUM. La variabilidad en los resultadossegún los diferentes parámetros de compresión se relacionócon el SNRT en ruido SM. Los resultados sugierenuna relación inversa entre el beneficio de la compresión yla severidad de la hipoacusia supra-liminar.