Binaural processing in hearing impairment
A typical complaint of those with hearing impairment is understanding speech in the presence of background noise. A laboratory measure used to assess performance in this situation is known as spatial release from masking (SRM). It has been established that normative SRM, using speech-shaped noise as the interferer, provides ~ 11 dB of benefit when the interferer moves from 0° to 112° azimuth (Plomp & Mimpem, 1981).
Many studies have reported a poorer SRM in those with hearing impairment (e.g. Noble et al. 1997). It would appear audibility is not a key predictor of SRM performance as there has been a varying level of correlation between SRM and PTA thresholds reported in the literature (e.g. Ter-Horst et al. 1993; Peissig & Kollmeier, 1997). Poor temporal fine structure (TFS) processing has been postulated as a reason behind the poorer performance of those with hearing impairment in SRM.
In this study we investigated the relationship between SRM, measures of binaural TFS processing and independent use of interaural time and level differences. Hearing loss has been reported to impact on binaural processing of TFS even when age is partialled out (King et al. 2014) so we would expect poorer SRM linked to poorer binaural TFS processing. In analysing results on an individual basis it is now emerging that our results are heterogeneous and do not support our predictions for this association. The independent use of different interaural cues and the link to SRM performance will help elucidate this matter.
King, A., Hopkins, K. & Plack, C. (2014). The effects of age and hearing loss on interaural phase discrimination. J. Acoust. Soc. Am. 135, 342-351.
Noble, W., Byrne, D. & Ter-Horst, K. (1997). Auditory localization, detection of spatial separateness, and speech hearing in noise by hearing impaired listeners. J. Acoust. Soc. Am. 102, 2343-2352.
Peissig, J. & Kollmeier, B. (1997). Directivity of binaural noise reduction in spatial multiple noise-source arrangements for normal and impaired listeners. J. Acoust. Soc. Am. 101, 1660-1670.
Plomp, R. & Mimpen, A. M. (1981). Effect of the orientation of the speaker’s head and the azimuth of a noise source on the speech-reception threshold for sentences. Acustica. 48, 325-328.
Ter-Horst, K., Byrne, D & Noble, W. (1993). Ability of hearing-impaired listeners to benefit from separation of speech and noise. Australian Journal of Audiology. Aust J Audiol. 15, 71-84.