Apparent Sound Displacement during Vestibular Stimulation

Abstract

Vestibular stimulation by means of angular acceleration around the midbody vertical axis produces a shift in the apparent position of a sound objectively rotating with the subject--the audiogyral illusion. Two possible explanations of the illusion were tested by a new method that leads to considerably reduced variance compared with previous methods. There were no significant differences in the extent of the illusion when stimulus tones of 500~, 1,024~, and 5,000~ were used. The illusion was significantly diminished in extent when the subjects strained their immobilized heads in the direction opposite from the usual apparent sound displacement during rotation. It is concluded that the illusion is based on a change in the felt position of the head rather than on differential hearing changes. Vestibular stimulation induced by acceleratory or deceleratory rotation around the midbody vertical axis (Z axis) produces various illusory effects.' One of these, the audiogyral illusion, consists of the apparent displacement of a sound that is objectively stationary with respect to the subject.2 The apparent displacement is opposite to the direction of rotation during acceleration and in the direction of original rotation during deceleration.3 Received for publication by Professor E. B. Newman. The investigation was supported by a National Science Foundation predoctoral grant to the first author and by Research Grant M-3658 from the National Institute of Mental Health, United States Public Health Service, to the second author. Dr. Lester is now at the State University College at Buffalo. 1I. P. Howard and W. B. Templeton, Human Spatial Orientation, 1966, 97-138. 2B. Clark and A. Graybiel, The effect of angular acceleration on sound localization: The audiogyral illusion, J. Psychol., 28, 1949, 235-244. 3 H. Munsterberg and A. H. Pierce, The localization of sound, in H. Munsterberg, Studies from the Harvard Psychological Laboratory, Psychol. Rev., 1, 1894, 461-476; A. H. Pierce, Studies in Auditory and Visual Space Perception, 1901; B. Bourdon, Sensations causees par des rotations passives de tout le corps, J. Psychol. (Paris), 30, 1933, 590-616; Clark and Graybiel (n. 2); M. D. Arnoult, Post-rotatory localization of sounds, this JOURNAL, 63, 1950, 229-236; L. B. W. Jongkees and R. A. van der Veer, On directional sound localization in unilateral deafness and its explanation, Acta otolaryng., 49, 1958, 119-131.