Benefit of Amplification at Low Input Levels in Normal-Hearing Listeners

Hearing devices such as hearables, personal sound amplification products, hearing aids, and active hearing protectors providing amplification in some settings are increasingly used by individuals with normal hearing. However, the benefits of providing amplification in this population remain unclear. This study investigated the effects of amplification on hearing thresholds, speech intelligibility in quiet, and experienced listening effort in normal-hearing listeners. Forty-four young adults with clinically normal hearing participated in two experiments comparing three conditions: open ear, aided with 0 dB insertion gain to approximate acoustic transparency, and aided with 15 dB flat insertion gain. Amplification was provided using a research hearing aid fitted with closed foam earplugs. Speech intelligibility was assessed with the Oldenburg Sentence Test, and experienced listening effort was measured using Adaptive CAtegorical Listening Effort Scaling (ACALES). Listening through the nominally transparent device introduced consistent disadvantages, including elevated hearing thresholds, reduced speech intelligibility, and increased listening effort. Providing 15 dB of amplification partially compensated hearing threshold elevation, fully restored speech intelligibility and reduced experienced listening effort beyond the unaided condition. Benefits of amplification at low input levels were primarily limited by the equivalent input noise of the hearing-aid microphones. These findings suggest that amplification can provide meaningful benefits for normal-hearing listeners at low speech levels, particularly when listening effort is considered alongside speech intelligibility. Future studies should examine these effects under more ecologically valid listening conditions, and potential benefits of increased amplification in hearing-impaired listeners.