On pitch-elevation mapping. Nature, nurture and behaviour

Abstract

The association between auditory pitch and spatial elevation is one the most fascinating examples of cross-dimensional mappings: in a wide range of cognitive, perceptual, attentional and linguistic tasks, humans consistently display a positive, sometimes absolute, association between auditory pitch and spatial elevation. However, the origins of such a pervasive mapping are still largely unknown.Through a combined analysis of environmental sounds and anthropometric measures, we demonstrate that, statistically speaking, this mapping is already present in both the distal and the proximal stimulus. Specifically, in the environment, high sounds are more likely to come from above; moreover, due to the filtering properties of the external ear, sounds coming from higher elevations have more energy at high frequencies.Next, we investigated whether the internalized mapping depends on the statistics of the proximal, or of the distal stimulus. In a psychophysical task, participants had to localize narrow band-pass noises with different central frequencies, while head- and world-centred reference frames were put into conflict by tilting participants’ body orientation. The frequency of the sounds systematically biased localization in both head- and world-centred coordinates, and, remarkably, in agreement with the mappings measured in both the distal and proximal stimulus.These results clearly demonstrate that the cognitive mapping between pitch and elevation mirror the statistical properties of the auditory signals. We argue that, in a shorter time-scale, humans learn the statistical properties auditory signals; while, in a longer timescale, the evolution of the acoustic properties of the external ear itself is shaped by the statistics of the acoustic environment.