A sensory misperception – like people bumping into a glass wall
Why do bats fly into walls, even though they can hear them? Researchers at Tel Aviv University conducted an experiment in which they released dozens of bats in a corridor blocked by objects of different sizes, made of different materials. To their surprise, the researchers discovered that the bats collided with large sponge walls (that produce a weak echo) as if they did not exist. The bats‘ behavior suggested that they did this even though they had detected the wall with their sonar system, indicating that the collision did not result from a sensory limitation, but rather from an acoustic misperception. The researchers hypothesize that the unnatural combination of a large object (wall) and a weak echo disrupts the bats‘ sensory perception and causes them to ignore the obstacle (much like people who bump into transparent walls).
The study was led by Dr. Sasha Danilovich then a PhD student in the lab of Prof. Yossi Yovel, Head of the Sagol School for Neuroscience and faculty member at the School of Zoology at the George S. Wise Faculty of Life Sciences. Other participants included Dr. Arian Bonman and students Gal Shalev and Aya Goldstein of the Sensory Perception and Cognition Laboratory at the School of Zoology and the Sagol School of Neuroscience. The paper was published in PNAS.
At the next stage of the experiment, the researchers methodically changed the features of the echoing objects along the corridor in terms of size, texture and echo intensity. They concluded that the bats‘ acoustic perception depends on a coherent, typical correlation of the dimensions with objects in nature. For example: large object- strong echo; small object – weak echo.
„Bats excel in acoustic perception. They are able to detect objects as tiny as mosquitoes, using sound waves,“ explains Prof. Yovel. „Using echolocation they can calculate the 3-dimensional location of both small and large objects, perceiving their shape, size and texture. To this end a bat’s brain processes various acoustic dimensions from the echoes returning from the object (such as frequency, spectrum and intensity). This perception is based on several senses that combine many different dimensions, such as color and shape.“
In addition, the researchers at TAU discovered that bats are not born with this ability. Repeating the experiment with young bats they found that they do not fly into walls. The study also found that adult bats can quickly learn the new correlations among the dimensions.
„By presenting the bats with objects whose acoustic dimensions are not coherent, we were able to mislead them, creating a misconception that caused them to repeatedly try to fly through a wall, even though they had identified it with their sonar. The experiment gives us a peek into how the world is perceived by these creatures, whose senses are so unique and different from ours,“ says Sasha Danilovich.