Effects of intermodulation distortion on speech intelligibility

Area of Science:

• Audiology
• Hearing Aid Technology
• Speech Perception

Background:

• Intermodulation distortion (IMD) is a common artifact in hearing aids.
• The impact of IMD on speech intelligibility, particularly for individuals with hearing loss, requires further investigation.

Purpose of the Study:

• To analyze intermodulation distortion in hearing aids.
• To assess the effect of hearing aid IMD on speech intelligibility in different listening conditions.

Main Methods:

• Four hearing aids were evaluated for IMD levels across frequencies.
• Speech intelligibility was tested using recorded sentences presented to normally hearing and sensorineurally impaired listeners in quiet and noise.

Main Results:

• Higher IMD levels were observed at lower frequencies (below 1 kHz).
• Low-frequency IMD significantly reduced speech intelligibility for sensorineural listeners in quiet.
• No significant intelligibility differences were found for normally hearing listeners or in noise conditions.

Conclusions:

• Low-frequency IMD can cause upward spread of masking, hindering high-frequency speech cue perception in sensorineural hearing loss.
• The masking effect of IMD is less apparent when a competing speech signal is present.