Unmasking is more effective, when images of noise and tone are in the different parts of the head. The stereo illusion is based on specific localizable images and highly correlated sounds at the two ears, perhaps differing only in timing or amplitude. Binaural unmasking vs. frequency Frequency does have a major effect on binaural unmasking. Example Binaural unmasking works well at 260 Hz but not at 4000 Hz. The coherent noise and the incoherent 4000 Hz tone localized in the same perceptual space - the center of the head.
Binaural unmasking seems to work better for lower frequencies.
At low frequencies, our ear respond to time differencies. At high frequencies, our ear respond to intensity and time differencies. The noise and a 260 Hz tone are applied to the left ear only. The tone is reduced until it is just masked by noise. As the same coherent noise is introduced to the right ear, the tone suddenly becomes audible in the left ear.