Effects of Directionality, Compression, and Working Memory on Speech Recognition.
Varsha Rallapalli, Gregory Ellis, Pamela Souza
PMID 33136708WHAT IT FOUND
In noise, fixed-directional settings reduced signal distortion from fast compression, but only at higher signal-to-noise ratios.
Working memory predicted speech recognition better when distortion was low. Directionality helps, but does not eliminate the cognitive cost of fast compression for everyone.
Key findings
01Fixed-directional processing reduced signal modification compared to omnidirectional settings when noise was present.
02At 10 dB SNR, fast-acting compression caused greater signal modification than slow-acting compression only in the omnidirectional setting, not in the fixed-directional setting.
03Working memory ability was significantly associated with speech recognition scores when signal modification was low (fixed-directional settings), but not when signal modification was high (omnidirectional settings).
STILL TO COME
How it was doneWhat they foundWhat it means for SLPs
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What it does not show
The study included only 23 participants, limiting the generalizability of the findings. The participants had normal cognitive functioning (MoCA >= 23), so results may not apply to patients with dementia or significant cognitive impairment. The study used a fixed-directional setting (hypercardioid), which may not represent the performance of adaptive or beamforming directional microphones commonly used in modern hearing aids. Signal modification was measured using a manikin (KEMAR) rather than real-ear measurements from the participants themselves, which may not perfectly capture individual ear acoustics. Working memory was correlated with degree of hearing loss in this cohort, making it difficult to fully separate the effects of cognition from audibility in some analyses.
Declared interests
The authors have no conflicts of interest to disclose. The study was supported by the National Institutes of Health.
The easy way to misread this
Do not assume that turning on directional microphones eliminates the negative impact of fast-acting compression on all patients. At lower signal-to-noise ratios (0 dB and 5 dB), fast compression still caused more signal distortion than slow compression, regardless of the directionality setting. Directional processing only neutralized the difference between fast and slow compression at the higher 10 dB SNR.