Do adaptive frequency response (AFR) hearing aids reduce 'upward spread' of masking?

Speech recognition scores in noise are improved for some subjects who wear hearing aids that reduce low-frequency noise with an adjustable high-pass filter circuit. To evaluate whether these improvements were related to a reduction in upward spread of masking, pure-tone masking patterns for a low-frequency band-pass noise were measured in normal and hearing-impaired subjects. The filter skirt of the noise masker was very steep, with attenuation above the 1000 Hz cutoff greater than 120 dB per octave. Masking patterns for the same noise were also obtained in the presence of a high-pass filter that simulated the effects of an adaptive frequency response (AFR) hearing aid. Differences in the masking patterns were considered a measure of upward spread of masking. On average, subjects with high-frequency hearing loss demonstrated greater amounts of upward spread of masking than did normal-hearing listeners. Further, monosyllabic speech recognition in noise testing indicated improvements in performance of the hearing-impaired subjects related to the decrease of upward spread of masking in the high-pass filtering conditions.