Speech perception with hearing aids: Effects of noise reduction and directional microphone systems on amplified signals

Our objective was to measure the variations of speech reception threshold (SRT) in noise induced by hearing aids with or without noise reduction (NR) and directional microphone systems (DM). Data were collected from 10 normal hearing volunteers wearing bilateral hearing aids and tested in a sound field of speech and noise. SRT was measured in function of: 1) speech source azimuth (0°,90°,180°); 2) background noise (monophonic vs. quadraphonic); 3) amplification (unaided vs. linearly aided); 4) amplification mode (linear, NR, DM, NR + DM). Compared using a hearing aid linear setting, NR does not improve the SRT in monophonic noise, while it improves the SRT by 2–3dB in quadraphonic noise with frontal and lateral speech. DM in monophonic noise improves frontal SRT (1dB) and worsens lateral and posterior SRT, while in quadraphonic noise frontal SRT is further advantaged and the DM negative effect disappears. With both devices activated a stronger positive effect is evident for frontal SRT in both noise fields (2–4dB) and for lateral SRT in quadraphonic noise. These results confirm that NR and DM can facilitate SRT in adverse noise conditions for normal hearing persons, and the results are useful as a reference for hearing impaired persons.