Masking of spondees by interrupted noise in hearing-impaired listeners.

The effects of changing the duty cycle of an interrupted-broad band masker on the spondee thresholds of hearing-impaired subjects were explored. Two diagnostic groups of sensorineural hearing loss, presbycusics and cochlear otosclerotics, were investigated. The interruption rate of the masker was 10/sec, and its duty cycle was varied at 25% intervals. Thresholds also were obtained in continuous noise and in quiet. Results when compared with earlier data from normal listeners revealed that subjects with sensorineural impairment exhibited poorer performance in all instances, including the continuous noise condition, when mean masker levels were adjusted to comparable sound pressure levels. The overall pattern of masking was more similar for the normal and hearing-impaired groups when performance was equated in terms of the mean threshold shift each group experienced in continuous noise. Even under these circumstances, however, hearing-impaired subjects demostrated notably greater residual masking under the 25 and 50% noise-on conditions. A major determinant of speech reception in fluctuating noise backgrounds is the dependence of the pattern of masking upon the difference between an individual's masked threshold in continuous noise and his threshold in quiet, rather than upon the sound pressure level of the masker.