Uncomfortable loudness levels in experienced unilateral and bilateral hearing aid users: Evidence of adaptive plasticity following asymmetrical sensory input?

Abstract

Abstract

Munro and Trotter [Inter J Audiol 45, 684-688, 2006] reported an asymmetry in uncomfortable loudness levels (ULLs) in a preliminary study using 12 experienced unilateral hearing aids users. The aim of the present study was to investigate ULLs in a larger sample of listeners with unilateral and bilateral hearing aid experience. Participants were adults with symmetrical high-frequency hearing impairment. There were 48 listeners with unilateral experience, 13 listeners with bilateral experience and a control group of 47 listeners with no hearing aid experience. The minimum duration of hearing aid experience was 2 years. ULLs were measured at 0.5, 1, 2 and 4 kHz. The unilateral group showed a statistically significant inter-aural asymmetry of 3-5 dB. Compared to the controls, there was a non-significant trend of higher ULLs in the fitted ear and lower ULLs in the not-fitted ear. ULLs in the bilateral group were symmetrical and similar to the control group. The findings suggest that changes in ULL may be a feature of asymmetrical sensory input and are consistent with a central gain mechanism.

Sumario

Munro y Rotter [Inter J Audiol 45, 684-688, 2006] reportaron asimetría en los niveles de molestia de intensidad subjetiva (ULLs) en un estudio preliminar, en el que participaron 12 usuarios experimentados unilaterales de auxiliares auditivos. El objetivo de este estudio fue investigar los ULLs en una muestra grande de usuarios, con experiencias uni o bilaterales. Los participantes fueron adultos con pérdida auditiva simétrica en frecuencias agudas y fueron 48 personas con experiencia unilateral, 13 con experiencia bilateral y un grupo control de 47 personas sin experiencia con auxiliares auditivos. La duración minima del uso de los auxiliares auditivos fue de 2 años. Se midieron las ULLs en 0.5, 1, 2 y 4 kHz. El grupo unilateral mostró una asimetría inter-aural de 3-5 dB, estadísticamente significativa. En comparación con los controles no hubo una tendencia significativa hacia mayores ULLs en el oído adaptado y menores ULLs en el oído sin auxiliar. Los ULLs en el grupo bilateral fueron simétricos y similares a los del grupo control. Estos hallazgos sugieren que los cambios en los ULL pueden ser un rasgo de estimulación sensorial asimétrico y que son consistentes con un mecanismo central de ganancia.

Key Words:

• Uncomfortable loudness level
• Hearing aid
• Acclimatisation
• Reorganisation
• Functional plasticity
• Central gain process

Acknowledgements

Grateful thanks to Chris Wynne, Audiology Department, Glan Clwyd hospital for facilitating data collection. The data were presented at the fourth annual convention of the British Academy of Audiology, 21-23 November 2007, Telford, UK. We are grateful to Professor Colette McKay and Dr Richard Baker who provided comments on an earlier draft of this manuscript.

Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.