Question
Are there any suggested fitting protocols to following with regards to fitting a patient with hearing aids who has been identified as having cochlear dead regions? Do protocols differ depending on whether the dead region is in the low frequency range versus the high frequency range?
Answer
There are not validated fitting protocols specifically for patients with cochlear dead regions. However, there has been quite a bit of research looking at how amplifying speech well within a dead region affects speech understanding. The results of these studies suggest that amplification needs do vary based on whether the dead region extends into the high or low frequency range.
Early research in this area focused on individuals with very severe high frequency hearing loss and dead regions that extended well into the high frequencies. Results suggested that these individuals benefited from amplification of speech to frequencies up to about 1.7 times the edge of the dead region. For example, if the dead region started at 2000 Hz, speech recognition improved with amplification up to about 3400 Hz. Recognition tended to remain the same or, in some cases, decrease if amplification was provided above this cutoff (Vickers et al., 2001;Baer et al., 2002).
Mackersie et al. (2004) did similar work in individuals with high frequency dead regions but with less hearing loss in the high frequencies (high-frequency thresholds
Although less work has been done in this area, current research suggests a somewhat different outcome in individuals with dead regions extending into the low frequencies. Vinay and colleagues (2007, 2008) suggest that for these individuals a low frequency cutoff of about 0.57 times the edge of the dead region to optimize speech recognition. For example, if a low frequency dead region starts at 1000 Hz and extends downward in frequency, amplification down to about 570 Hz would be beneficial. In contrast to outcomes in individuals with high frequency dead regions, extending amplification well into the low frequency dead region frequently resulted in a decrease in performance. In some cases the degradation was quite large (e.g., up to 30%) No such degradation was observed in the control group (low frequency hearing loss but no dead regions). These findings suggest that knowledge of the presence or absence of dead regions in individuals with low frequency hearing loss may be particularly important.
For a review of this topic and how to identify individuals with dead regions see Moore (2004) or my online course OC Fittings: Potential Impact of Cochlear Dead Regions on OC Candidacy
Benjamin W.Y. Hornsby, Ph.D. is an Assistant Professor at Vanderbilt University. His current research interests include the perceptual abilities of persons with hearing loss and how they impact the design, implementation and efficacy of hearing aids and other auditory prosthetics.
References
Baer, T., Moore, B. C. and Kluk, K. (2002). Effects of low pass filtering on the intelligibility of speech in noise for people with and without dead regions at high frequencies. J Acoust Soc Am 112(3 Pt 1): 1133-44.
Cox, R., Alexander, G., Johnson, J., Rivera, I. (2011). Cochlear dead regions in typical hearing aid candidates: Prevalence and implications for use of high-frequency speech cues. Ear and Hearing 32(3), 339 - 348.
Mackersie, C. L., Crocker, T. L. and Davis, R. A. (2004). Limiting high-frequency hearing aid gain in listeners with and without suspected cochlear dead regions. J Am Acad Audiol 15(7): 498-507.
Moore, B. C. (2004). Dead regions in the cochlea: conceptual foundations, diagnosis, and clinical applications. Ear Hear 25(2): 98-116.
Vinay and Moore, B. C. (2007). Speech recognition as a function of high-pass filter cutoff frequency for people with and without low-frequency cochlear dead regions. J Acoust Soc Am 122(1): 542-53.
Vinay, Baer, T. and Moore, B. C. (2008). Speech recognition in noise as a function of highpass-filter cutoff frequency for people with and without low-frequency cochlear dead regions. J Acoust Soc Am 123(2): 606-9.
