Effect of hearing aids on speech perception in noisy situations.

Hearing-impaired people often complain about poor speech intelligibility when they are in noisy surroundings. Several authors have published data suggesting that hearing aids add distortion to the signal and thus make speech less intelligible. Given the tendency of people to speak louder in competing noise, it means that some patients might understand better in such circumstances without an aid than with an aid. The present study investigated the effect of modern commercial hearing aids on the ability of patients to understand speech monaurally in noisy circumstances. The results in general showed speech to be equally understandable with and without an aid if the effects of presentation level (amplification) are excluded. The results, however, varied considerably between patients. Statistical analysis showed that the variance could be explained primarily by the degree of high-frequency loss and the slope of the audiogram. Patients with steep sloping audiograms understand better and patients with a conductive hearing loss component understand less in noisy circumstances with a hearing aid. Speech intelligibility in noisy situations did not correlate at all with the hearing loss averaged over the mid-frequencies (500, 1,000 and 2,000 Hz) but it did correlate with the high-frequency hearing loss (2,000 and 4,000 Hz) and the slope of the audiogram, indicating the importance of high-frequency emphasis in hearing aids.