Minimum audible movement angles as a function of sound source trajectory.

Auditory resolution of moving sound sources was determined in a simulated motion paradigm for sources traveling along horizontal, vertical, or oblique orientations in the subjects's frontal plane. With motion restricted to the horizontal orientation, minimum audible movement angles (MAMA) ranged from about 1.7 degrees at the lowest velocity (1.8 degrees/s) to roughly 10 degrees at the highest velocity (320 degrees/s). With the sound moving along an oblique orientation (rotated 45 degrees relative to the horizontal) MAMAs generally matched those of the horizontal condition. When motion was restricted to the vertical, MAMAs were substantially larger at all velocities (often exceeding 8 degrees). Subsequent tests indicated that MAMAs are a U-shaped function of velocity, with optimum resolution obtained at about 2 degrees/s for the horizontal (and oblique) and 7-11 degrees/s for the vertical orientation. Additional tests conducted at a fixed velocity of 1.8 degrees/s along oblique orientations of 80 degrees and 87 degrees indicated that even a small deviation from the vertical had a significant impact on MAMAs. A displacement of 10 degrees from the vertical orientation (a slope of 80 degrees) was sufficient to reduce thresholds (obtained at a velocity of 1.8 degrees/s) from about 11 degrees to approximately 2 degrees (a fivefold increase in acuity). These results are in good agreement with our previous study of minimum audible angles long oblique planes [Perrott and Saberi, J. Acoust. Soc. Am. 87, 1728-1731 (1990)].(ABSTRACT TRUNCATED AT 250 WORDS)