The effects of hearing loss on the importance of high- and low-frequency information to speech understanding

Recent research results have suggested that sensorineural hearing loss (SNHL) has a larger detrimental effect on high- than low-frequency speech information. To examine the effect of SNHL on the importance of low- and high-frequency speech information, sentence recognition in noise was assessed in multiple high, low, and band widening filter conditions. Study subjects included a hearing loss group (HI), consisting of persons with essentially “flat” SNHL, and a control group of subjects with normal hearing (NHS), listening to the same materials under comparable conditions of audibility and presentation level. Masked thresholds in the speech background noise were also obtained to ensure that the levels of masking noise, rather than auditory thresholds, determined audibility for both groups. Finally, the role that cochlear dead regions may play in limiting the utility of speech information in specific frequency regions was examined.; Results suggest that SNHL reduces the contribution of speech information across a wide frequency range. This general reduction in scores across all filter conditions can be explained, in part, by the elevation of thresholds in noise for the HI subjects compared to the NHS group. On average, masked thresholds for the HI were about 5 dB greater than those for the NHS group and did not vary significantly across frequency. In contrast to recent reports, however, the HI subjects in this study were able to use high frequency information, as well or better than low frequency information, to improve their speech understanding. In addition, the patterns of performance changes were similar for the HI group and the NHS group suggesting that hearing loss causes a uniform rather than frequency-specific degradation of speech information, at least for subjects with flat SNHL. Finally, despite substantially poorer speech recognition performance of the HI subjects, compared to the NHS group, no evidence of large-scale cochlear dead regions was found. This indicates that cochlear dead regions are not a prerequisite for SNHL to have a significant negative impact on speech understanding.