Ruth Y. Litovsky
Dept. of Neurophysiol., 273 Med. Sci. Bldg., Univ. of Wisconsin, Madison, WI 53706
Neil A. Macmillan
Univ. of Massachusetts, Amherst, MA 01003
Minimum audible angle (MAA) was measured in free field with a center position at 0(degrees), and 25(degrees) or 50(degrees) on the right. Stimuli were 6-ms-wide band noise bursts presented as single bursts or noise pairs under precedence-effect conditions. In the single-noise condition, one burst was presented from the right or left. In precedence lead discrimination, a leading sound was presented from the left or right speaker and a lagging sound from a speaker at center. In precedence lag discrimination, the lagging sound was on the right or left and the leading sound was at center. The test stimulus was either presented in isolation or was preceded by a single standard noise at center. MAAs were lowest for the single condition, slightly higher for lead discrimination, and much higher for lag discrimination. Presence of a standard yielded a benefit in lag discrimination, especially at 0(degrees). Thresholds at 50(degrees) were significantly higher than at 0(degrees) and 25(degrees), especially in lag discrimination. The data can be described by a model in which judgments are based on apparent azimuth of the fused stimulus, and the lagging sound in a pair perceptually ``pulls'' the image along the azimuth dimension. [Work supported by NSF and NIH.]