Using the Mismatch Negativity to Evaluate Hearing Aid Directional Enhancement Based on Multistream Architecture.

OBJECTIVES

To evaluate whether hearing aid directivity based on multistream architecture (MSA) might enhance the mismatch negativity (MMN) evoked by phonemic contrasts in noise.

DESIGN

Single-blind within-subjects design. Fifteen older adults (mean age = 72.7 years, range = 40 to 88 years, 8 females) with a moderate-to-severe degree of sensorineural hearing loss participated. Participants first performed an adaptive two-alternative forced choice phonemic discrimination task to determine the speech level-that is, signal to noise ratio (SNR)-required to reliably discriminate between two monosyllabic stimuli (/ba/ and /da/) presented in the presence of ongoing fixed-level background noise. Participants were then presented with a phonemic oddball sequence alternating on each trial between two loudspeakers located in the front at 0° and -30° azimuth. This sequence presented the same monosyllabic stimuli in the same background noise at individualized SNRs determined by the phonemic discrimination task. The MMN was measured as participants passively listened to the oddball sequence in two hearing aid conditions: MSA-ON and MSA-OFF.

RESULTS

The magnitude of the MMN component was significantly enhanced when evoked in MSA-ON relative to MSA-OFF conditions. Unexpectedly, MMN magnitudes were also positively related to degrees of hearing loss. Neither MSA nor the participant's hearing loss was found to independently affect MMN latency. However, MMN latency was significantly affected by the interaction of hearing aid condition and individualized SNRs, where a negative relationship between individualized SNR and MMN latency was observed only in the MSA-OFF condition.

CONCLUSIONS

Hearing aid directivity based on the MSA approach was found to improve preattentive detection of phonemic contrasts in a simulated multi-talker situation as indexed by larger MMN component magnitudes. The MMN may generally be useful for exploring the underlying nature of speech-in-noise benefits conferred by some hearing aid features.