MINIMAL UPWARD SPREAD OF MASKING - CORRELATIONS WITH SPEECH AND AUDITORY BRAIN-STEM RESPONSE MASKED THRESHOLDS

Much less than predicted upward spread of masking, termed undermasking , was previously noted in three elderly listeners, who are the focus o f this report. Three aspects of undermasking were studied: Reliability , facilitation of speech recognition in noise, and correlation with ph ysiological measurements. The masker was a 90-dB-SPL 1-kHz low-pass-fi ltered noise. Reliability of undermasking was assessed from serial mea surements made over an approximately 2-year interval. Masked speech th resholds were measured with an adaptive procedure for two types of sti muli: spondaic words and the California Consonant Test. Subjects with undermasking had substantially lower masked speech thresholds than eit her 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 mas ked behavioral threshold, suggesting that the mechanism producing unde rmasking is in the auditory periphery.