Sounds use tricks to deceive the human ear

Sounds use tricks to deceive the human ear

Investigators on August 19. Roaring snakes increase their roaring speed as potential threats approach, and this sudden change to high frequency mode makes listeners, including humans, believe they are closer than they actually are.N. The Magazine Current Biology.

“Our data show that the loud presentation of a snake, which has been interpreted as a simple sound warning of a snake’s presence for decades, is actually a more complex communication signal between species,” says Boris Chagno, senior author at Carl-Frances – Grass University. “The abrupt change to high frequency mode acts as a smart signal that misleads the listener about the actual distance between the sound source and thus, if the listener misinterprets the distance, a distance limit is created.”

Snake-wagging tails wag their tails strongly to warn other animals of their presence. Previous research has shown that the frequency of cracking varies, but very little is known about the nature of this phenomenon or the message it conveys to listeners. Evidence of this riddle was obtained by visiting an animal sanctuary, where Sharghota noticed

This image shows the western back of a diamond ready to panic. Attribution: Tobias Cole

Based on this simple observation, Shagone and his team conducted experiments in which bodies move toward screaming. One of the ones they used was a human-like trunk, and the other — a pop-up black tablet — seemed to get closer and closer as it grew. As potential threats approached, the vibration frequency increased to approximately 40 Hz and then abruptly moved to the higher frequency range from 60 to 100 Hz.

Additional results showed that the Rattlesman adjusted their vocalization speed based on the approach speed rather than the size of the object. “In real life, oars use extra vibration and infrared signals to detect mammalian approaches, so we expect noisy responses to be stronger,” says Chagno.

To test how others perceive this change in crawling speed, the researchers created a virtual reality environment in which 11 participants were taken to a snake hidden in a meadow. As people approached, its whistle frequency increased rapidly to an imaginary distance of 4 m, up to 70 Hz. Listeners were asked to indicate when a sound source appeared one meter away. The gradual increase in frequency prompted participants to reduce the distance between themselves and the imaginary snake.

“Snakes not only announce their presence, but have also developed an innovative solution: an audible distance signal similar to that seen in reverse cars,” says Chagno. Evolution is a random process, the result of thousands of experiments involving large mammals that we can understand from today’s perspective as a majestic design. The snake evolved through experimentation and error, disturbing the auditory perception of mammals, leaving snakes that could avoid trampling snakes. “

Reference: “Frequency modulation of rattlesnake snake width affects human perception of voice distance,” Michael Forstofer, Michael Shot, Harold Lush, Tobias Cole, Lutz Wegreb, Boris B. Chagno, 2021. August 19 Current Biology.
DOI: 10.1016 / j.cub.2021.07.018

Funding was provided by the Munich Center for Neuroscience.

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