Differences between psychophysical "suppression effects" under diotic and dichotic listening conditions.

A forward-masking paradigm was used in an attempt to measure and compare "suppression effects" under one monaural system condition, NOSO, and two binaural system conditions, NOSM and NOSII. The signal was a 500-Hz tone burst of 10-ms duration (measured at the 6-dB down points) and was presented 12.5 ms after the termination of the masker. In the diotic condition, as the masker bandwidth increased, masking at first increased, reached a maximum between bandwidths of 50 and 150 Hz, and then decreased with further increases of the bandwidth. The pattern of results was very different for the dichotic conditions: Here, masking never decreased with increases in the masker bandwidth; unlike the NOSO condition, there was no evidence of a "suppression effect." These data are used to argue that diotic "suppression effects" obtained with noiseband maskers are actually produced by a combination of off-frequency listening and quality-difference cues.