An Evaluation of Hearing Aid Beamforming Microphone Arrays in a Noisy Laboratory Setting.

BACKGROUND: People with hearing loss experience difficulty understanding speech in noisy environments. Beamforming microphone arrays in hearing aids can improve the signal-to-noise ratio (SNR) and thus also speech recognition and subjective ratings. Unilateral beamformer arrays, also known as directional microphones, accomplish this improvement using two microphones in one hearing aid. Bilateral beamformer arrays, which combine information across four microphones in a bilateral fitting, further improve the SNR. Early bilateral beamformers were static with fixed attenuation patterns. Recently adaptive, bilateral beamformers have been introduced in commercial hearing aids.

PURPOSE: The purpose of this article was to evaluate the potential benefits of adaptive unilateral and bilateral beamformers for improving sentence recognition and subjective ratings in a laboratory setting. A secondary purpose was to identify potential participant factors that explain some of the variability in beamformer benefit.

RESEARCH DESIGN: Participants were fitted with study hearing aids equipped with commercially available adaptive unilateral and bilateral beamformers. Participants completed sentence recognition testing in background noise using three hearing aid settings (omnidirectional, unilateral beamformer, bilateral beamformer) and two noise source configurations (surround, side). After each condition, participants made subjective ratings of their perceived work, desire to control the situation, willingness to give up, and tiredness.

STUDY SAMPLE: Eighteen adults (50-80 yr, M = 66.2, σ = 8.6) with symmetrical mild sloping to severe hearing loss participated.

DATA COLLECTION AND ANALYSIS: Sentence recognition scores and subjective ratings were analyzed separately using generalized linear models with two within-subject factors (hearing aid microphone and noise configuration). Two benefit scores were calculated: (1) unilateral beamformer benefit (relative to performance with omnidirectional) and (2) additional bilateral beamformer benefit (relative to performance with unilateral beamformer). Hierarchical multiple linear regression was used to determine if beamformer benefit was associated with participant factors (age, degree of hearing loss, unaided speech in noise ability, spatial release from masking, and performance in omnidirectional).

RESULTS: Sentence recognition and subjective ratings of work, control, and tiredness were better with both types of beamformers relative to the omnidirectional conditions. In addition, the bilateral beamformer offered small additional improvements relative to the unilateral beamformer in terms of sentence recognition and subjective ratings of tiredness. Speech recognition performance and subjective ratings were generally independent of noise configuration. Performance in the omnidirectional setting and pure-tone average were independently related to unilateral beamformer benefits. Those with the lowest performance or the largest degree of hearing loss benefited the most. No factors were significantly related to additional bilateral beamformer benefit.

CONCLUSIONS: Adaptive bilateral beamformers offer additional advantages over adaptive unilateral beamformers in hearing aids. The small additional advantages with the adaptive beamformer are comparable to those reported in the literature with static beamformers. Although the additional benefits are small, they positively affected subjective ratings of tiredness. These data suggest that adaptive bilateral beamformers have the potential to improve listening in difficult situations for hearing aid users. In addition, patients who struggle the most without beamforming microphones may also benefit the most from the technology.