ABSTRACT
Resonant cavities of the external ear transform the spectrum of an incident sound, thereby introducing potential cues to the location of the sound source. Human subjects apparently rely on spectral shape cues for localiza tion in the vertical and front/back dimensions, but it is not clear whether spectra shape cues also aid in horizontal localization. We tested the ability of normal listeners to localize 1/6-octave-wide noise bursts that varied in azimuth and elevation. Subjects localized these sounds accurately in the horizontal dimension, whereas they made systematic errors in the vertical and front/back dimensions. The patterns of errors could be predicted by a model that compared stimulus spectra with the transfer functions of the external ears. The normal localization in the horizontal dimension could be accounted for by interaural difference cues. To confound interaural differ ence cues, we measured localization of broadband sounds under monaural conditions. Normal-hearing subjects who wore a plug in one ear showed a systematic localization bias toward the hearing ear, but a population of congenitally monaural patients showed reasonably accurate localization, both in horizontal and vertical dimensions. The results suggest that interaural differences, when present, are the predominant cue for horizontal localiza tion. In the absence of such cues, however, spectral shape cues can provide useful cues to horizontal sound source location.
