Directional Benefit Is Present with Audiovisual Stimuli: Limiting Ceiling Effects

Background: Past research demonstrates that as the speech recognition performance of listeners fitted with omnidirectional hearing aids approaches maximum (ceiling), the benefit afforded by directional microphones is necessarily lessened. This effect could potentially eliminate the benefit provided by directional microphones in easier listening situations, such as environments with visual cues and favorable signal-to-noise ratios (SNRs). Purpose: The purpose of this study was to evaluate directional benefit using auditory-visual stimuli in SNRs commonly found in the real world (ranging from +3 to +12 dB). In order to maximize the possibility of directional benefit, a bilateral beamformer was used, which functions as a highly directional microphone. Research Design: Sentence recognition was evaluated in three SNRs and in two levels of reverberation (low and moderate). For each SNR and reverberation combination, sentence recognition was evaluated using omnidirectional and bilateral beamformer microphone modes. Study Sample: A total of 15 adults with hearing loss participated. Only listeners who had significant difficulty understanding speech in noise were included. Data Collection and Analysis: Sentence recognition scores were evaluated using analysis of variance with three within-participant variables (SNR, reverb, microphone mode). Follow-up analyses were conducted using linear contrast while controlling for family-wise error rate. Results: Results revealed significant bilateral beamformer benefit ranging from approximately 22–30 rationalized arcsine units (˜20–28 percentage points) in both low and moderate reverberation across all tested SNRs (+3 to +12 dB). Conclusions: These results provide support for the use of bilateral beamformers, even at relatively favorable SNRs and in the presence of visual cues, for listeners who demonstrate poor sentence recognition in noise.

Factors Influencing Individual Variation in Perceptual Directional Microphone Benefit

Background: Large variations in perceptual directional microphone benefit, which far exceed the variation expected from physical performance measures of directional microphones, have been reported in the literature. The cause for the individual variation has not been systematically investigated. Purpose: To determine the factors that are responsible for the individual variation in reported perceptual directional benefit. Research Design: A correlational study. Physical performance measures of the directional microphones obtained after they had been fitted to individuals, cognitive abilities of individuals, and measurement errors were related to perceptual directional benefit scores. Study Sample: Fifty-nine hearing-impaired adults with varied degrees of hearing loss participated in the study. Data Collection and Analysis: All participants were bilaterally fitted with a Motion behind-the-ear device (500 M, 501 SX, or 501 P) from Siemens according to the National Acoustic Laboratories' non-linear prescription, version two (NAL-NL2). Using the Bamford-Kowal-Bench (BKB) sentences, the perceptual directional benefit was obtained as the difference in speech reception threshold measured in babble noise (SRTn) with the devices in directional (fixed hypercardioid) and in omnidirectional mode. The SRTn measurements were repeated three times with each microphone mode. Physical performance measures of the directional microphone included the angle of the microphone ports to loudspeaker axis, the frequency range dominated by amplified sound, the in situ signal-to-noise ratio (SNR), and the in situ three-dimensional, articulation-index weighted directivity index (3D AI-DI). The cognitive tests included auditory selective attention, speed of processing, and working memory. Intraparticipant variation on the repeated SRTn's and the interparticipant variation on the average SRTn were used to determine the effect of measurement error. A multiple regression analysis was used to determine the effect of other factors. Results: Measurement errors explained 52% of the variation in perceptual directional microphone benefit (95% confidence interval [CI]: 34–78%), while another 37% of variation was explained primarily by the physical performance of the directional microphones after they were fitted to individuals. The most contributing factor was the in situ 3D AI-DI measured across the low frequencies. Conclusions: Repeated SRTn measurements are needed to obtain a reliable indication of the perceptual directional benefit in an individual. Further, to obtain optimum benefit from directional microphones, the effectiveness of the microphones should be maximized across the low frequencies.

Effect of Age on Directional Microphone Hearing Aid Benefit and Preference

Background: Despite the recognition that the directional microphone hearing aid (DMHA) is an important intervention aimed at helping older hearing-impaired adults understand speech in noisy environments, there is little evidence that older listeners can actually benefit from directional processing. Purpose: The objective of this study was to determine if older and younger adults can obtain and perceive comparable benefit afforded by DMHAs. Study Sample: Twenty-four hearing-impaired adults aged 36 through 79 yr were fit with switchable-microphone hearing aids and tested in the laboratory and the field. Data Collection and Analysis: In the laboratory, the listeners’ directional benefit and preferences for microphone modes (directional vs. omnidirectional) were assessed using various speech-recognition-in-noise tests. In the four-week field trial, a paired-comparison technique and paper-and-pencil journals were used to determine the benefit provided by directional processing. The effects of age on directional benefit/preference were analyzed using generalized linear models with controlling for the effect of hearing loss. Results: The results revealed that age did not have a significant effect on directional benefit and preference as measured in the laboratory. However, the field data showed that older age was significantly associated with a lower preference for the directional mode. Conclusion: These results indicate that although listeners of different ages may obtain and perceive comparable benefit from DMHAs in laboratory testing, older users tend to perceive less benefit than do younger users in the real world. The implications of these findings are discussed.