Auditory detection, discrimination and speech processing in ageing, noise-sensitive and hearing-impaired listeners.

The aims of this research were to document changes in hearing and speech intelligibility in noise that occur with ageing, noise sensitivity, and progressive bilateral sensorineural hearing loss. Five groups defined by age, clinical complaint and degree of hearing loss were tested. Each of 73 subjects participated in nine different procedures, including detection in quiet and in continuous 90 dB SPL helicopter noise, frequency and duration discrimination, consonant recognition and word identification. The effects of different types of background noise and speech-to-noise ratio were investigated. Ageing, without concomitant hearing loss, resulted in significantly greater DLs both for frequency and for duration with a 20 ms standard at both 500 Hz and 4,000 Hz. Hearing loss, unconfounded by ageing, affected masked detection and frequency discrimination at 4,000 Hz and speech intelligibility in noise. The sole finding for subjects with noise sensitivity was an upward spread of masking for detection. Across tests, the best predictors of speech processing decrements were the detection thresholds for 2,000 Hz and 4,000 Hz in quiet or in noise.