MONAURAL SOUND LOCALIZATION REVISITED

Research reported during the past few decades has revealed the importa nce for human sound localization of the so-called ''monaural spectral cues.'' These cues are the result of the direction-dependent filtering of incoming sound waves accomplished by the pinnae. One point of view about how these cues are extracted places great emphasis on the spect rum of the received sound at each ear individually. This leads to the suggestion that an effective way of studying the influence of these cu es is to measure the ability of listeners to localize sounds when one of their ears is plugged. Numerous studies have appeared using this mo naural localization paradigm. Three experiments are described here whi ch are intended to clarify the results of the previous monaural locali zation studies and provide new data on how monaural spectral cues migh t be processed. Virtual sound sources are used in the experiments in o rder to manipulate and control the stimuli independently at the two ea rs. Two of the experiments deal with the consequences of the incomplet e monauralization that may have contaminated previous work. The result s suggest that even very low sound levels in the occluded ear provide access to interaural localization cues. The presence of these cues com plicates the interpretation of the results of nominally monaural local ization studies. The third experiment concerns the role of prior knowl edge of the source spectrum, which is required if monaural cues are to be useful. The results of this last experiment demonstrate that extra ction of monaural spectral cues can be severely disrupted by trial-to- trial fluctuations in the source spectrum. The general conclusion of t he experiments is that, while monaural spectral cues are important, th e monaural localization paradigm may not be the most appropriate way t o study their role. (C) 1997 Acoustical Society of America.