Why auditory pitch and spatial elevation get high together :
Shape of human ear may have evolved to mirror acoustics in natural world
Have you ever wondered why most natural languages invariably use the same spatial attributes — high versus low — to describe auditory pitch? Or why, throughout the history of musical notation, high notes have been represented high on the staff? According to a team of neuroscientists from Bielefeld University and the Max Planck Institute for Biological Cybernetics in Tübingen, high pitched sounds feel ‘high’ because, in our daily lives, sounds coming from high elevations are indeed more likely to be higher in pitch. This study has just appeared in the science journal PNAS.
Dr. Cesare Parise and colleagues set out to investigate the origins of the mapping between sound frequency and spatial elevation by combining three separate lines of evidence. First of all, they recorded and analyzsed a large sample of sounds from the natural environment and found that high frequency sounds are more likely to originate from high positions in space. Next, they analyzed the filtering of the human outer ear and found that, due to the convoluted shape of the outer ear — the pinna — sounds coming from high positions in space are filtered in such a way that more energy remains for higher pitched sounds. Finally, they asked humans in a behavioural experiment to localize sounds with different frequency and found that high frequency sounds were systematically perceived as coming from higher positions in space.
The results from these three lines of evidence were highly convergent, suggesting that all such diverse phenomena as the acoustics of the human ear, the universal use of spatial terms for describing pitch, or the reason why high notes are represented higher in musical notation ultimately reflect the adaptation of human hearing to the statistics of natural auditory scenes. ‘These results are especially fascinating, because they do not just explain the origin of the mapping between frequency and elevation,’ says Parise, ‘they also suggest that the very shape of the human ear might have evolved to mirror the acoustic properties of the natural environment. What is more, these findings are highly applicable and provide valuable guidelines for using pitch to develop more effective 3D audio technologies, such as sonification-based sensory substitution devices, sensory prostheses, and more immersive virtual auditory environments.’
The mapping between pitch and elevation has often been considered to be metaphorical, and cross-sensory correspondences have been theorized to be the basis for language development. The present findings demonstrate that, at least in the case of the mapping between pitch and elevation, such a metaphorical mapping is indeed embodied and based on the statistics of the environment, hence raising the intriguing hypothesis that language itself might have been influenced by a set of statistical mappings between naturally occurring sensory signals.
Besides the mapping between pitch and elevation, human perception, cognition, and action are laced with seemingly arbitrary correspondences, such as that yellow-reddish colors are associated with a warm temperature or that sour foods taste sharp. This study suggests that many of these seemingly arbitrary mappings might in fact reflect statistical regularities to be found in the natural environment.
The Cognitive Neuroscience Group of the Biological Faculty is affiliated to the Center of Excellence Cognitive Interaction Technology (CITEC) at Bielefeld University. The group is focusing on human multisensory perception, sensorimortor integration, perceptual learning, and human-machine interaction. The researchers combine human psychophysical experimentation with computational modeling. The group currently consists of 15 members from a variety of different backgrounds: biology, cognitive science, psychology, medicine, physics, and engineering.
The Max Planck Institute for Biological Cybernetics uses experimental, theoretical, and methodological approaches to investigate cognitive processes. It employs approximately 300 employees from over 40 countries and is located at the Max Planck Campus in Tübingen. The Max Planck Institute for Biological Cybernetics is one of 80 institutes and research facilities belonging to the Max Planck Society for the Advancement of Science.
The Bernstein Center Tübingen is part of the National Bernstein Network for Computation Neuroscience. With this initiative, the Federal Ministry of Education and Research (BMBF) has been supporting the new research field of computation neuroscience with more than 170 million Euros since 2004.
- C. V. Parise, K. Knorre, M. O. Ernst. Natural auditory scene statistics shapes human spatial hearing. Proceedings of the National Academy of Sciences, 2014; DOI: 10.1073/pnas.1322705111