The effects of hearing protection on speech intelligibility in noise

Abstract

Speech intelligibility was investigated in subjects with and without the use of hearing protection in a high noise environment. Fifteen normal hearing subjects and fifteen subjects with high-frequency hearing losses were given the California Consonant Test (CCT) with and without the use of a circurnaural muff-type hearing protector. The CCT was selected as the test stimuli due to its design as a sensitive measure for persons experiencing a high-frequency hearing loss. Testing was conducted in a sound-treated room with the speech and noise stimuli delivered at a high intensity level (85dBA); signal-to-noise ratio was zero.

A two-way analysis of variance on the resulting CCT scores indicated a significant difference between the normal hearing subject scores and the hearing impaired subject scores. Statistical significance was also found between the CCT scores obtained with hearing protection and those obtained without hearing protection. Interaction effects between hearing sensitivity and the hearing protection condition were not significant. However, examination of raw score means indicated a trend toward decreased CCT scores with hearing protection use for the hearing impaired subject group. Individual variability in the CCT scores may have accounted for the lack of significance in the interaction effects. A factor in this variability probably was the broad range of muff attenuation values for the experimental subjects. Future research is recommended to identify factors which cause variability in hearing protection attenuation across individual users.

Future researchers may also focus upon investigating specific variables such as test stimuli, noise levels, signal-to-noise ratios, types of noise, or types of hearing protection. Research in this area is needed to further study the effects of hearing protection onspeech intelligibility in high noise environments.