Does proximity govern judgments of auditory direction in the azimuthal plane?

Abstract

In an experiment analogous to that of Shepard which showed circularity in judgments of relative pitch of pairs of octave-complex tones [Shepard, J. Acoust. Soc. Am. 36, 2346–2353 (1964)], 40 listeners, centered in a sound-attenuated room, judged the apparent direction (clockwise, or counterclockwise) of 396 pairs of successive complex tones emanating from all possible pairs of 12 speakers spaced at 30-degree intervals on an imaginary circumference. Judgments were influenced by speaker proxim-ity and in general mirrored the pattern for judgments of up–down direction associated with the phenomena of circular pitch observed by Shepard. In contrast to Shepard’s pitch judgment task, musical training did not increase sensitivity in the judgment of auditory spatial direction. Unique to the spatial task was the finding that approximately one-half the subjects showed systematic front–back confusion. When this confusion was taken into account, proximity effects were even more apparent. For diametrically opposed speakers (at 180-degrees absent proximity cues), direction was theoretically ambiguous, but listeners showed a small but significant clockwise bias, reminiscent of Deutsch’s tritone paradox for octave-complex tones [Deutsch, Kuyper, and Fisher, Music Percept. 5, 79–92 (1987)]. [Work supported by NSERC.]