Minimum audible movement angles for sources varying in both elevation and azimuth

A minimum audible movement angle (MAMA) experiment was performed in a “simulated motion” paradigm which allowed travel along vertical, horizontal, or oblique paths. Velocities of travel ranged from 1.8–230°/s. With motion restricted to the horizontal plane, MAMA thresholds increased from about 1.7° at the lowest velocity (1.8 °/s) to roughly 10° at a simulated velocity of 230°/s. With the sound traveling on an oblique plane (45° rotation above the horizontal) MAMA thresholds generally matched those of the horizontal condition. When the motion was restricted to the vertical plane (the array was rotated 90° from the horizontal) MAMA thresholds were substantially higher at all velocities than thresholds observed in the other array orientations, often exceeding 8° even at low velocities. Post hoc tests conducted at oblique planes 80° and 87° indicated that the slightest deviation from the vertical, had a significant impact on MAMA thresholds. A deviation of 10° from the vertical orientation was sufficient to reduce thresholds to those obtained when the sound moves on the horizontal plane (0° rotation above horizontal). These results suggest: (1) the ability to detect motion is essentially independent of the path traveled with one noted exception; sources traveling on an absolute vertical dimension, and (2) detection of the direction of travel is possible with azimuth changes of only a few tenths of a degree if concurrent changes in elevation are available. Some implications of these results are discussed. [Work supported by NSF and NIH.]