ASA 127th Meeting M.I.T. 1994 June 6-10

5aPP18. Additivity of notched-noise and broadband-noise masking in normal-hearing and hearing-impaired listeners.

Marjorie R. Leek

Van Summers

Army Audiol. & Speech Ctr., Walter Reed Army Med. Ctr., Washington, DC 20307-5001

Walt Jesteadt

Boys Town Natl. Res. Hospital, Omaha, NE 68131

The threshold elevations produced by a combination of two or more maskers can be modeled as the sum of nonlinear transformations of the individual masker effects, along with an additional compressed term representing the listener's threshold in quiet [L. E. Humes and W. Jesteadt, J. Acoust. Soc. Am. 85, 1285--1294 (1989)]. In this study, this modified power law (MPL) model has been applied to data recently published by Leek and Summers [M. R. Leek and V. Summers, J. Acoust. Soc. Am. 94, 3127--3137 (1993)]. They used notched-noise maskers to measure auditory filter shapes at 500 and 2000 Hz in quiet and in 20- or 35-dB spectrum level broadband noise in both normal-hearing and hearing-impaired listeners. Thresholds measured in combined notched and broadband noise are well-predicted from the individual masker effects according to the MPL model. Best-fitting compression parameters indicate greater linearity at 500 Hz than at 2000 Hz, but no significant difference in linearity between listeners with normal hearing and those with hearing loss. We are currently exploring alternative analyses of the data for hearing-impaired listeners, based on treating their sensitivity loss as an additional internal masker added to normal quiet thresholds. [Work supported by NIDCD.]