(back to SpatialLocalizationPaper)

The ability to locate sounds in space represents a complex, highly evolved system of acoustic and psychoacoustic processes that greatly aid our overall awareness. These skills enabled humans to survive by locating predator and prey, and in turn ingrained some habits that aid the auditory system: we look toward a source to identify it, then make small head movements to extract more points of reference. In a present day environment, the necessity to base life-or-death decisions on aural cues is removed, but the underlying principles remain intact. In fact, they continue to contribute to modern lifestyle in diverse ways. A blind person can navigate a room with acuity incredible to a sighted observer; a couple can converse intelligibly in a noisy restaurant; an audio enthusiast can experience a symphony in his living room. In this paper we explore how the ear achieves these feats, and how modern technology can best exploit them.

Before we begin, let's explain some terminology likely to arise in a discussion of spatial hearing. Sound will describe physical phenomena, the actual waves and vibrations that in turn give rise to auditory events, the perceptions recorded by the human nervous system. In fact, we should note that in general there is not a direct causal link. Auditory events like tinnitus or artificial stimulation have no corresponding vibration; sound waves above 20 KHz or masked by other sounds may not be perceived at all (Blauert, 3). In turn, we observe two distinct kinds of localization: the location and directionality of a sound source in the physical world, and those of an observer's mental image. Only the latter will be denoted localization from here on, reserving terms such as 'position' for physical locations; the minimum recognizable change will be the localization blur.

Positions will usually be described in relation to three planes. The horizontal plane defines our usual front-to-rear and left-to-right orientation; the frontal plane cuts the head vertically between the face and rear, thus containing L/R and up/down dimensions; the median plane slices between the left & right halves of the head, encoding front/back and up/down information. When auditory events are localized inside the head, we call the perceived positions lateralization since these feelings are usually described as existing on one left/right axis.

By experimenting with sound sources varied along these positions -- as correlated with human responses -- much can be learned of the auditory space in which we reside. Particularly, we recognize that the localization of auditory events is a major factor, if not the primary one, in distinguishing between them. We will focus on two cases: where physical and auditory localization coincide, we seek to understand how & why; and where they do not, we shall demonstrate some applications of "fooling" the auditory system.

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