Understanding the speech-understanding problems of the hearing impaired.

This article presents a tutorial overview of the speech-recognition difficulties of the hearing impaired. Much recent research indicates that the primary problem underlying the speech-recognition difficulties of the hearing impaired is the loss of hearing sensitivity and accompanying loudness recruitment. This tutorial demonstrates why loss of hearing sensitivity plays such an important role and why hearing aids fitted with contemporary fitting strategies provide only limited benefit in noise for many of these individuals. In addition, low-pass noise is often said to present the hearing-impaired listener with greater difficulties than broad-band noise. This observation is also explained quite simply by careful consideration of the loss of hearing sensitivity. Finally, two clinical articulation index (AI) calculation schemes, designed to quantify the effects of hearing loss on speech understanding, are reviewed and evaluated.