Minimal upward spread of masking: correlations with speech and auditory brainstem response masked thresholds

Much less than predicted upward spread of masking, termed undermasking, was previously noted in three elderly listeners, who are the focus of this report. Three aspects of undermasking were studied: Reliability, facilitation of speech recognition in noise, and correlation with physiological measurements. The masker was a 90-dB-SPL 1-kHz low-pass-filtered noise. Reliability of undermasking was assessed from serial measurements made over an approximately 2-year interval. Masked speech thresholds were measured with an adaptive procedure for two types of stimuli: spondaic words and the California Consonant Test. Subjects with undermasking had substantially lower masked speech thresholds than either audiometrically matched elderly subjects or young, normal-hearing subjects. It appears that undermasking is a stable characteristic that provides the listener with exceptionally good communication abilities in noise. Finally, a strong positive correlation was observed between the masked auditory brainstem response (wave V) threshold and the masked behavioral threshold, suggesting that the mechanism producing undermasking is in the auditory periphery.