Mental Health Res. Inst., Univ. of Michigan, Ann Arbor, MI 48109-0720
Small differences in the frequency of pure tones are heard as changes in loudness, either when the tones are presented within the same ear (monaural beats) or when presented to the separate ears (binaural beats). With complex tones, comparable differences in fundamental frequency (asynchrony) are heard as changes in roughness or musicality. With two fundamental frequencies presented to each ear, a wide combination of monaural and binaural roughness changes are produced. Under conditions where monaural and binaural roughness changes are clearly detected, the identification of which one of the two ears is asynchronous (one ear asynchronous, the other ear synchronous) is at chance. Substantial interaural differences in intensity are required for the successful uncoupling of the asynchronous ear.