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 noise extended below and above the signal, at lower and higher signal frequencies, 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 maskers as a function of masker bandwidth. Bandpass-masker bandwidth was increased by introducing noise components below and above the signal frequency while keeping the noise centered on the signal frequency, and also by adding noise below the signal only, and above the signal only. Subjects were younger 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 with some physiological evidence of stronger suppression below a fiber's characteristic frequency than above. For subjects with normal hearing, suppression was greater at higher than at lower frequencies. For older subjects with hearing loss, suppression was reduced to a greater extent above the signal than below and where thresholds were elevated. Suppression for older subjects with normal hearing was poorer than would be predicted from their absolute thresholds, suggesting that age may have contributed to reduced suppression or that suppression was sensitive to changes in cochlear function that did not result in significant threshold elevation.