Perception of moving sounds: velocity discrimination

Two experiments investigated auditory velocity perception. Exper. I compared auditory to visual velocity estimates. Five adults judged, in miles/hr, the motion of a sound source (a small loudspeaker) moving on a 1.88-m boom around S's head at each of 7 velocities from 15 to 360 degrees/sec. The sound source was either visible or not visible. Velocity judgments were shown in both modalities to be a power function of source velocity, with a slope of approximately 0.90. No significant difference was found between the auditory and visual functions. A control Exper. II determined with 14 naive adults that the similarities between the functions in each modality could not be attributed to either previous visual experience or proprioceptive feedback. Ss estimated the velocity of the visible moving loudspeaker while tracking the source with their eyes (N: 7) or while fixating on a small stationary light (N: 7). Eye motion was recorded from electrodes on the canthi. No significant differences were found between these conditions. The estimates were again shown to be a power function of source velocity (though slightly higher slopes of 0.99 for visual pursuit and 1.0 for visual fixation were obtained than in Exper. I). These experiments suggest a surprising degree of similarity in the perception of velocity in auditory and visual spatial functions.