Localizing Sounds Revolving At Very High Velocities: An Auditory Wagon Wheel Effect

Abstract

Localizing sound sources as they move around us is a critical function of the auditory system. Yet most research focuses on static sound sources or sources moving at slow velocities. The present work explores circular trajectories at very high velocities well above the velocity at which we lose the sense of direction (~2.5 rot/s with white noise). As the number of rotations per second approaches the fundamental frequency of the spinning sound, a sense of direction re-emerges. This creates what has been described informally as the auditory equivalent to the wagon-wheel effect: the sound appears to move in one direction when the velocity is below the fundamental frequency, and it appears to move in the opposite direction when the velocity is above the fundamental frequency. We report on an experiment testing this effect with a 200-Hz complex sound using adaptive VBAP spatialization on a 16-loudspeaker array. The experiment (N=22) confirmed that participants perceived opposite directions whether the velocity is below or above the fundamental frequency. Moreover, that there is a shift of apparant direction depending on the velocity of the stimulus: when the velocity is above the fundamental frequency of the stimulus, the perceived direction is the actual direction. However, when the velocity is below the fundamental frequency, the perceived direction is opposite to the actual direction.