Off-frequency masking for monaural and binaural detection

Measures of critical bands reveal larger binaural than monaural critical bands [J. C. Sever, Jr., and A. M. Small, Jr., J. Acoust. Soc. Am. 66, 1343–1349 (1979)]. To date, the largest binaural critical band reported for a 500-Hz pure tone signal is 220 Hz [J. W. Hall, R. S. Tyler, and M. A. Fernandes, J. Acoust. Soc. Am. 73, 894–898 (1983)]. Our study suggests an appreciably larger binaural critical band when a procedure other than the traditional bandlimiting approach is used. We determined So and Sπ thresholds for a 500-Hz pure tone masked by an No 50-Hz narrow band of noise centered at 500 Hz. Then, to the 50-Hz masker, we added a 30-Hz narrow band of noise centered at one of 11 different frequencies from 200–2000 Hz. The 50-Hz band was always No whereas the 30-Hz band was No or Nπ. We observed increases in binaural thresholds when 30-Hz narrow bands of noise as far as 500 Hz from the signal were added. These results suggest that a masking noise spectrum as wide as 1000 Hz influences binaural threshold for a 500-Hz pure tone; a value almost five times larger than previously reported estimates.