Effect of forward and backward masking on speech intelligibility.

Abstract

Monaural-intelligibility functions for monosyllabic words were obtained for seven subjects with normal hearing under the following major experimental conditions: (1) speech interrupted by silence at the rates of 1, 10, and 100 interruptions per second (ips); (2) speech alternating with noise (80 dB SPL) at rates of 1, 10, and 100 ips; (3) speech in interrupted noise (80 dB SPL) at rates of 1, 10, and 100 ips. The comparison between the intelligibility functions for Conditions 1 and 2 yielded a measure of the effects of forward and backward masking during the noise-free interval. The comparison between the intelligibility functions for Conditions 2 and 3 yielded a measure of the extent to which the speech signal during the noise burst contributed to intelligibility. The results indicated that the effect of forward and backward masking on intelligibility was substantial at 10 ips and even more pronounced at 100 ips. However, at 1 ips little masking effect was observed except at very adverse signal-to-noise (S/N) ratios. The findings also demonstrated that the speech heard within the noise burst contributed to intelligibility at favorable S/N ratios when the noise was interrupted one time per second. At 100 ips, the speech signal within the noise burst made only a small contribution to the total intelligibility score, and at 10 ips the function was formed almost entirely by the speech heard during the noise-free intervals.