Modern spatial audio reproduction techniques with headphones or loudspeakers seek to control the perceived spatial image as accurately as possible in three dimensions. The mechanisms of spatial perception have been studied mainly in the horizontal plane, and this article attempts to shed some light on the corresponding phenomena in the median plane. Spatial perception of concurrently active sound sources was investigated in an exploratory listening experiment. Incoherent noise source distributions of varying spatial characteristics were presented from loudspeaker arrays in anechoic conditions. The arrays were coinciding with the ±45° angular sectors in the frontal median and horizontal planes. The task for immobile subjects was to report the directions of loudspeakers they perceived emitting sound. The results from median plane distributions suggest that two concurrent sources located along the vertical midline can be perceived individually without resorting to head movements when they are separated in elevation by 60° or more. With source pairs separated by less than 60°, and with more complex physical distributions, the distributions were perceived inaccurately, biased, and spatially compressed but nevertheless not as point-like auditory images.
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