Trajectory perception in the free field

Abstract

Using virtual sound sources in an echo-attenuated chamber, the sensitivity of subjects to the direction of linear auditory motion was evaluated. Four sighted and four blind subjects participated. Subjects reported the perceived trajectory by orienting a freely rotating pointer. Subjects fell into two distinct categories: those who performed well at the task, and those who did not, with blind subjects tending to be in the first category and sighted subjects the second. Those subjects performing well at the task also showed improved performance with increasing linear velocity. Because the only stimulus parameter associated with increased linear velocity was frequency envelope, it can be concluded that frequency changes resulting from the Doppler effect can improve the accuracy of auditory trajectory perception. The same subjects performed discrimination tasks measuring sensitivity to changes in azimuthal acceleration, as well as to changes in amplitude and frequency envelopes. Two models of trajectory perception are considered: A Psychoacoustical Parameters Model uses a weighted combination of specific perceptual abilities such as sensitivity to azimuthal acceleration, and to changes in amplitude and frequency envelopes. An Informational Masking Model is considered as a possible explanation for those subjects demonstrating poor performance in the trajectory perception task.