Detection of Time Differences and Level Differences from a Position away from the Median Plane

Abstract

By the use of an interaural phase difference of 90° a 50-Hz band of noise, centered at 500 Hz was delayed to the right ear by 0.5 msec. The resultant sound was perceived as lying well to the left of the median plane. To this continuous noise was added a signal from the same noise source so arranged in phase that the signal plus masker appeared to lie either inward or outward from the continuous masker. The signal plus masker could also be moved inward or outward by introducing a difference of level into the two earphone channels. Detection of these movements was compared with detection of movements away from the median plane by employing the N0Sπ condition with α=90° to obtain a time difference, or α=0° to obtain a level difference relative to the median plane. The results show that detection of a time difference from a position away from the median plane is inferior to detection of a time difference around the median plane. However, the results for a difference of level showed no such advantage for the median plane; detection was the same from both reference positions. The findings are taken as further indication of the relative independence of the time mechanism and the level mechanism of the auditory nervous system. [Supported in part by a grant from the Public Health Service, National Institute of Neurological Diseases and Stroke.]