Abstract
Auditory pitch has an intrinsic spatial connotation: Sounds are high or low, melodies rise and fall, and pitch can ascend and descend. In a wide range of cognitive, perceptual, attentional, and linguistic functions, humans consistently display a positive, sometimes absolute, correspondence between sound frequency and perceived spatial elevation, whereby high frequency is mapped to high elevation. In this paper we show that pitch borrows its spatial connotation from the statistics of natural auditory scenes. This suggests that all such diverse phenomena, such as the convoluted shape of the outer ear, the universal use of spatial terms for describing pitch, or the reason why high notes are represented higher in musical notation, ultimately reflect adaptation to the statistics of natural auditory scenes.Human perception, cognition, and action are laced with seemingly arbitrary mappings. In particular, sound has a strong spatial connotation: Sounds are high and low, melodies rise and fall, and pitch systematically biases perceived sound elevation. The origins of such mappings are unknown. Are they the result of physiological constraints, do they reflect natural environmental statistics, or are they truly arbitrary? We recorded natural sounds from the environment, analyzed the elevation-dependent filtering of the outer ear, and measured frequency-dependent biases in human sound localization. We find that auditory scene statistics reveals a clear mapping between frequency and elevation. Perhaps more interestingly, this natural statistical mapping is tightly mirrored in both ear-filtering properties and in perceived sound location. This suggests that both sound localization behavior and ear anatomy are fine-tuned to the statistics of natural auditory scenes, likely providing the basis for the spatial connotation of human hearing.
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