Aided cortical auditory evoked potentials in response to changes in hearing aid gain

Abstract

Abstract

Objective: There is interest in using cortical auditory evoked potentials (CAEPs) to evaluate hearing aid fittings and experience-related plasticity associated with amplification; however, little is known about hearing aid signal processing effects on these responses. The purpose of this study was to determine the effect of clinically relevant hearing aid gain settings, and the resulting in-the-canal signal-to-noise ratios (SNRs), on the latency and amplitude of P1, N1, and P2 waves. Design & Sample: Evoked potentials and in-the-canal acoustic measures were recorded in nine normal-hearing adults in unaided and aided conditions. In the aided condition, a 40-dB signal was delivered to a hearing aid programmed to provide four levels of gain (0, 10, 20, and 30 dB). As a control, unaided stimulus levels were matched to aided condition outputs (i.e. 40, 50, 60, and 70 dB) for comparison purposes. Results: When signal levels are defined in terms of output level, aided CAEPs were surprisingly smaller and delayed relative to unaided CAEPs, probably resulting from increases to noise levels caused by the hearing aid. Discussion: These results reinforce the notion that hearing aids modify stimulus characteristics such as SNR, which in turn affects the CAEP in a way that does not reliably reflect hearing aid gain.

Sumario

Objetivo: Existe interés en el uso de los potenciales evocados auditivos corticales (CAEP) para evaluar la adaptación de auxiliares auditivos y la plasticidad relacionada con la experiencia, asociada a la amplificación; no obstante, se sabe poco sobre los efectos del procesamiento de las señales de los auxiliares auditivos sobre esas respuestas. El propósito de esta investigación fue determinar el efecto clínicamente relevante de los ajustes de ganancia de auxiliares auditivos y las relaciones señal/ruido (SNR) resultantes en el conducto auditivo, sobre la latencia y la amplitud de las ondas P1, N1 y P2. Diseño y muestra: Se registraron en nueve adultos normoyentes los potenciales evocados y las mediciones acústicas en el conducto auditivo externo en condiciones de amplificación o sin ella. En la primera condicion, se envió una señal de 40-dB al auxiliar auditivo programado para proveer cuatro niveles de ganancia (0, 10, 20 y 30 dB). Como control, se parearon niveles de estímulos sin amplificación con las salidas de los estímulos amplificados (p.ej., 40, 50, 60 y 70 dB) para efectos comparativos. Resultados: Cuando los niveles de la señal están definidos en términos de niveles de salida, los CAEP con amplificación fueron sorprendentemente menores y tardíos que los CAEP sin amplificación, probablemente como resultado de los incrementos en los niveles de ruido, causados por el auxiliar auditivo. Discusion: Estos resultados refuerzan la idea de que los auxiliares auditivos modifican las características de los estímulos como la SNR, la cual a su vez afecta los CAEP en una forma que no refleja confiablemente la ganancia del auxiliar auditivo.

Key Words::

• Cortical auditory evoked potentials (CAEPs)
• Event-related potentials (ERPs)
• Signals in noise
• Signal-to-noise ratio (SNR)
• N1
• Auditory cortex
• Hearing aids
• Amplification

Acknowledgements

The authors wish to thank Pamela Souza for helpful discussions about these data, and Wendy Tolin for assistance with data processing. This work was supported by the National Institutes of Health through the National Institute on Deafness and Other Communication Disorders, and the Department of Veterans Affairs through the Rehabilitation Research and Development Service [F31-DC007296 and C6971M (CJB); R01-DC007705 (KLT); P30-DC004661].

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

Notes

1. We use the term ‘aided CAEPs’ to refer to CAEPs recorded from an individual who is wearing a hearing aid at the time of testing, such that sound field stimuli are processed by the hearing aid and delivered to the individual's ear canal.