Frequency selectivity as a potential measure of noise damage susceptibility.

The notched-noise procedure of Patterson (1974, Journal of the Accoustical Society of America, 55, 802-809; 1976, Journal of the Acoustical Society of America, 59, 640-654) was employed in revealing changes in auditory frequency selectivity (FS) in noise-exposed industrial workers in manufacturing plants in which noise levels in the working environment exceeded 90 dB(A). With 4 kHz as the test frequency, both threshold and FS measures were applied to three groups of non-exposed young adults (total N = 61) for reference values and to workers in three different factories, some ('noise-exposed') working in noise levels over 90 dB(A) (total N = 222). In another study involving 185 workers only the FS test was repeated after a work session, and the results are reported on 31 who worked in high noise levels. Pre-work-shift data showed that when thresholds were better than 30-dB HL most FS values were 10 dB or more, while subjects with hearing threshold levels beyond that showed reduced FS. Two post-work-shift studies of 144 ears of the noise-exposed workers showed significant deleterious changes in both thresholds and FS but the relationships were different in the two studies. The findings indicate that the notched-noise test is sensitive to noise-induced auditory damage, even after a single work-shift. Attractive features of the procedure are that it reduces the need for a quiet test environment and that it can be more resistant to testee manipulation or threshold 'learning' effects, often seen in industrial audiometric testing.