Background-Patients with unilateral sensorineural hearing loss (USNHL) experience great difficulty listening to speech in noisy environments. A directional microphone (DM) could potentially improve speech recognition in this difficult listening environment. It is well known that DMs in behind-the-ear (BTE) and custom hearing aids can provide a greater signal-to-noise ratio (SNR) in comparison to an omnidirectional microphone (OM) to improve speech recognition in noise for persons with hearing impairment. Studies examining the DM in bone anchored auditory osseointegrated implants (Baha), however, have been mixed, with little to no benefit reported for the DM compared to an OM.

Digital signal processing (DSP) has provided significant advances and improvements in hearing aid technology. These advances, and the increased processing speed that DSP offers, have resulted in improved and expanded features in current hearing aid technology. These advances have also served to expand the fitting range of amplification for patients who previously could not benefit from amplification. This article reviews the advances and supporting research in specific hearing aid features, devices, and assistive technology developments that allow a greater number of patients access to amplification. These features and devices include directional microphones, Bluetooth and other wireless technology, digital noise reduction, devices for patients with single-sided deafness, frequency transposition, selflearning and adaptation managers, and integrated real ear measures. Despite the changes in hearing aids created by DSP, limitations still exist. Additionally, peer-reviewed research is not yet available to support the reported benefits of some of these advances.