Vertical sound source localization when listeners and sounds rotate: The Wallach vertical illusion

Abstract

In addition to testing his prediction that listeners would use changes in binaural cues relative to listeners’ self-induced head movements to disambiguate front-back confusions, Wallach (1939) also tested his calculations that the relative rate at which these binaural cues change could be used by listeners to determine the elevation of the sound source. Wallach was able to induce the illusion that a sound source rotating along the azimuth plane was perceived as though it were above the listener. We sought to replicate and expand upon Wallach’s study. We rotated listeners in a specialized chair at constant velocity. We presented filtered Gaussian noises at bandwidths of one-tenth octave, two octaves, and broadband, using center frequencies of 500 Hz and 4 kHz from a ring of 24 azimuthal loudspeakers located at pinna height. Sounds could also be presented from loudspeakers elevated relative to pinna level. The relative rates of sound and listener rotation around the azimuth plane were varied according to the relationship established by Wallach (1939) and listeners made judgments about the perceived elevation and rotation of the sounds. [Partially supported by a grant from the National Institute on Deafness and Other Communication Disorders, NIDCD.]