Speech intelligibility in noise-induced hearing loss: effects of high-frequency compensation

The speech-recognition ability of six listeners with permanent noise-induced hearing losses above 1 kHz was evaluated with the Pascoe High-Frequency Work List spoken by a female talker and presented in the field. In experiment I the words were presented at five intensity levels through five different amplification systems (one with a uniform response and four with increasing amounts of high-frequency emphasis). In experiment II the frequency response of the system associated with the highest scores in experiment I was modified in four ways: elimination of frequences above 6.3 kHz, addition and deletion of 1/3-octave emphasis at the low-frequency boundary of the hearing loss, and addition of 6-dB high-frequency emphasis. The frequency response that was associated with the highest word-identification score for each listener had between 20 and 33 dB more gain in the frequency region of the hearing loss than did the uniform response. Three major factors were found to affect the work-identification scores: audibility of the speech energy, separation of the third-octave-band levels of the words from the discomfort threshold, and balance between the low- and high-frequency levels of the speech signal.