Threshold Shifts Produced by Pulsed and Continuous Maskers at Equal Sound Pressure and Effective Masking Levels

The effectiveness of pulsed and continuous masking was investigated as a function of frequency, with the masker presented at equal sound‐pressure levels and then at equal effective‐masking levels. Thresholds at 250, 1000, and 4000 cps were recorded by 10 subjects via a graphic attenuator while a wide‐band random noise was delivered either to the test ear (monotic) or the contralateral ear (dichotic). Three methods of presentation were used: (1) pulsed tone and pulsed noise, simultaneous; (2) pulsed tone and continuous noise; and (3) continuous tone and continuous noise. In both the monotic and dichotic conditions, the effectiveness of the pulsed masker, whether presented at equal sound‐pressure levels or at effective levels, increased with signal frequency. The threshold shifts in the monotic and dichotic conditions also increased with frequency but the changes were slightly less than for the pulsed‐pulsed condition. When noise was present, changes in the variability around threshold as estimated by frequency of excursions over time were observed under certain conditions. This finding was related to the theoretical interpretation of the results. [This work was supported by the National Institutes of Health, U. S. Department of Health, Education, and Welfare.]