Amazing stuff!
"Thanks to their incredibly sensitive hearing, barn owls can hunt down rodents and other tiny prey even on the darkest of nights. One ear is positioned slightly higher than the other, allowing these nocturnal predators to precisely locate sounds in both the vertical and horizontal planes. By rapidly integrating information from both ears, the bird’s brain can construct a three-dimensional map of auditory space.
Humans, by contrast, have symmetrical ears and lack such mental maps. Even so, we’re fairly good at localizing sounds and readily adapt to changes in ear shape and hearing sensitivity that affect the way we perceive spatial cues. ...
To find out, scientists fitted human listeners with custom-made asymmetrical ear molds and tested their ability to localize different types of sound. Study participants wore the molds continuously for up to 5 weeks, only taking them off to sleep. The wearers’ ability to localize sounds in the horizontal plane was largely unaffected, the team reports in a bioRxiv preprint. But the participants had a much harder time determining the vertical position of sounds. This ability did improve over time, but adaptation was limited, suggesting that the human brain can only partially remap spatial dimensions. ..."
From the abstract:
"The brain computes sound location from auditory spatial cues. Humans and barn owls can localize sounds with high accuracy, yet they rely on fundamentally different cue configurations shaped by their ear anatomy and neural circuitry.
In humans, symmetrical ears provide interaural time and level differences for horizontal localization, while vertical localization depends primarily on high-frequency, monaural spectral cues generated by the pinnae.
Barn owls, by contrast, possess asymmetrical ears and use binaural cues to localize sounds in both azimuth and elevation. Because auditory pathways are assumed to be tuned to the statistics of species-specific cues, it remains unclear whether humans can localize sounds using barn-owl-like spatial information.
We addressed this by fitting human listeners with asymmetric ear molds that disrupted normal spectral cues and introduced elevation-dependent interaural level differences, while preserving interaural time differences. Participants wore the molds during daily life and were tested on sound localization using broadband, high-pass, and low-pass noise.
Acute exposure to the molds severely degraded elevation localization, while horizontal localization remained largely unaffected. With prolonged exposure, elevation localization improved, but adaptation was limited. Crucially, improvement was strongest for broadband sounds. Because broadband sounds uniquely provide access to both low-frequency interaural time differences and high-frequency interaural level differences, this pattern indicates that listeners learned to use binaural cues to infer sound elevation.
These findings demonstrate that the human auditory system can partially adapt to extreme barn-owl-like outer-ear acoustics. Binaural cues can be repurposed to support elevation localization, with effective learning requiring access to complementary spatial cues."
Figure 1. Acoustic spatial cues in humans and barn owls.
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