Psychophysical suppression measured with bandlimited noise extended below and/or above the signal: Effects of age and hearing loss

The objectives of this study were to measure suppression with bandlimited n oise extended below and above the signal, at lower and higher signal freque ncies, between younger and older subjects, and between subjects with normal hearing and cochlear hearing loss. Psychophysical suppression was assessed by measuring forward-masked thresholds at 0.8 and 2.0 kHz in bandlimited m askers as a function of masker bandwidth. Bandpass-masker bandwidth was inc reased by introducing noise components below and above the signal frequency while keeping the noise centered oil the signal frequency, and also by add ing noise below the signal only, and above the signal only. Subjects were y ounger and older adults with normal hearing and older adults with cochlear hearing loss. For all subjects, suppression was larger when noise was added below the signal than when noise was added above the signal, consistent wi th some physiological evidence of stronger suppression below a fiber's char acteristic frequency than above. For subjects with normal hearing, suppress ion was greater at higher than at lower frequencies. For older subjects wit h hearing loss, suppression was reduced to a greater extent above the signa l than below and where thresholds were elevated. Suppression for older subj ects with normal hearing was poorer than would be predicted from their abso lute thresholds, suggesting that age may have contributed to reduced suppre ssion or that suppression was sensitive to changes in cochlear function tha t did not result in significant threshold elevation. (C) 2001 Acoustical So ciety of America.