Characterizing the Speech Reception Threshold in hearing-impaired listeners in relation to masker type and masker level.

The Speech Reception Threshold [SRT, (dB SNR)] is often used as an outcome measure to quantify the acuity for speech perception in noise. The majority of studies observe speech intelligibility in noise at a fixed noise level. However, the observed SNR might be an ambiguous outcome measure because it is dependent on the sensation level (SL) of the noise in the case of a non-stationary noise. Due to their higher thresholds, hearing-impaired listeners are usually tested at a different SL compared to normal-hearing listeners. Therefore, the observed SNR "itself" might not be a robust outcome measure to characterize the differences in performance between normal-hearing and hearing-impaired listeners, within and between different studies. In this paper, the SRTs are measured at a fixed absolute noise level (80 dBA) and at a fixed SL (25 dB). The results are discussed and described with an extension to the SRT model of Plomp [(1986). "A signal-to-noise ratio model for the speech-receptionthreshold of the hearing-impaired," J. Speech Hear. Res. 29, 146-154] and the Extended Speech Intelligibility Index. In addition, two alternative outcome measures are proposed which are, in contrast to the SNR, independent of the noise level. These outcome measures are able to characterize the SRT performance in fluctuating noise in a more uniform and unambiguous way.