Fitting and Evaluating a Hearing Aid for Recipients of a Unilateral Cochlear Implant: The NAL Approach

32 THE HEARING REVIEW AUGUST 2004 reach the right ear a bit sooner than it will reach the left ear. It will also be slightly louder in the right than in the left ear. This head diffraction effect will enhance speech intelligibility in noise when speech and noise come from different sides of the head, because the brain can selectively attend to the ear with a better signal-to-noise ratio (SNR) for understanding speech. Even when the same signal and noise reach both ears, the brain can combine both inputs to produce more salient central representations of the speech signal (binaural redundancy) than if only input from one ear is available. The brain can also make use of the inter-aural time differences to partially reduce the deleterious effect of noise (binaural squelch). For unilateral cochlear implant users who have residual hearing in the nonimplanted ear, it is possible to provide binaural hearing by fitting a hearing aid to that ear. Increasing evidence points to the binaural benefits that are possible with the use of bimodal hearing devices, including improved speech intelligibility, better sound localization, and functional improvements in real-life environments. This article examines this research and discusses clinical issues related to bimodal device use.