Interaural phase locking as a function of interaural level

Abstract

Sinusoidal phase modulation in a sinusoidal carrier was monaurally presented to observers’ left ears in standard two-interval forced-choice experiments: The carrier was phase modulated in one of two randomly chosen observation intervals and the observers were required to indicated the interval having phase modulation. In the dichotic condition, a pure tone with the same frequency (500 Hz) and level (70 dB SPL) as the carrier was presented to the right ear in both observation intervals; in the monaural condition, the pure tone was attenuated by 71 dB. The 1.5-s stimuli were gated simultaneously with 20-ms Gaussian rise/fall times. At low modulation rates, the depth of phase modulation corresponding to 75% correct responses in the dichotic condition was an order of magnitude smaller than in the corresponding monaural condition consistent with the results of G. G. R. Green, J. S. Heffer, and D. A. Ross [J. Physiol. (London) 260, 49P–50P (1976)]. The dichotic advantage is scarcely affected by two orders of magnitude reduction in the level of the pure tone in the right ear. The results are related to the precision of phase locking in the auditory system. [Work supported by the Royal Society.]