DIOTIC AND DICHOTIC DETECTION USING MULTIPLIED-NOISE MASKERS

Detection thresholds were measured with a multiplied-noise masker that was in phase in bath ears and a sinusoidal signal which was either in phase or out of phase (NoSo and NoS pi conditions). The masker was ge nerated by multiplying a low-pass noise with a sinusoidal carrier. The signal was a sinusoid with the same frequency as the carrier and a co nstant phase offset, upsilon, with respect to the carrier. By adjustin g the phase offset, the stimulus properties were varied in such a way that only interaural time delays (upsilon = pi/2) or interaural intens ity differences (upsilon = 0) were present within the NoS pi stimulus. Thresholds were measured at a center frequency of 4 kHz as a function of bandwidth for upsilon = pi/2 and for upsilon = 0. In a second expe riment thresholds were measured for a bandwidth of 25 Hz as a function of the center frequency. The results show that narrow-band BMLDs at 4 kHz can amount to 30 dB for the upsilon = 0 condition. For this condi tion, narrow-band BMLDs are also reasonably constant across frequency, in contrast to results obtained with standard Gaussian-noise maskers. For upsilon = pi/2, BMLDs are restricted to the frequency region belo w 2 kHz provided that the masker is narrow band, but BMLDs of up to 15 dB are found at 4 kHz if the masker is 50 Hz or wider. The frequency dependence of the binaural thresholds seems to be best explained by as suming that the stimulus waveforms are compressed before binaural inte raction. (C) 1998 Acoustical Society of America.