Researchers at Tel Aviv University have found that fruit bats are able, to some extent, to translate echo-acoustic information — information gleaned from bouncing sound waves off of objects — into 3D shapes, and are thus able to visually recognize objects they first perceived just acoustically.
The study sheds some light on how bats and possibly other mammals and humans integrate sensory perceptions of sounds, tastes, vision and smell.
The researchers studied three aspects of multisensory integration in Egyptian fruit bats, according to a paper published on Wednesday in Science Advances.
The study showed that bats are able to translate echo-acoustic information into a visual representation. They use only vision to learn the three-dimensional shape of an object and during navigation are able to “dynamically switch” between the modalities; vision was given more weight when deciding where to fly, while echolocation was more dominant when approaching an obstacle, the researchers said.
“How animals — including humans — integrate information from different sensory modalities is a major question that still puzzles scientists,” said Prof. Yossi Yovel of the George S. Wise Faculty of Life Sciences, who led the study. “Imagine, for example, that you see a car coming from the right, but you hear another one coming from the left. How will your brain process and integrate this information?”
“It is an open fundamental question in sensory perception” of how mammals and bats integrate multi-modal sensory information, he said in a phone interview. The study is a step forward in addressing it, he added.
The study shows that in bats, “sensory modalities are integrated” and “sometimes vision is more important, sometimes echolocation is more important and sometimes it changes during the performance of the task,” he said.
Bats use echolocation, sending out sound waves from the mouth or nose to navigate. When the sound waves hit an object, they produce echoes, which return to the bats’ ears.
Bats are also creatures of the night and are accustomed to complete darkness. They use their hypersensitive hearing to feed, to fend off prey and to mate.
“Contrary to popular belief, bats do indeed see, and many of them do use their eyes as much as they use echolocation,” Sasha Danilovich, who conducted the study, said in a statement. “But how they integrate vision and echolocation is poorly understood. Our new findings shed light on how fruit bats really operate in darkness.”
In their experiment, over several months, the researchers let the bats navigate their way through objects in complete darkness, using just echolocation. Then, they switched on the lights and put the objects in plastic containers. This neutralized the bats’ ability to get echoes back from the objects.
“We found that the bats were able to recognize these objects anyway,” Yovel said.
“Can you smell something and know what its shape is? Probably not, unless you are already familiar with it,” Yovel said. “But we showed that bats can hear something, or hear the echo of something, and they can translate this into some kind of visual representation.”
“They have some kind of representation that gives them some insight of what the object should look like,” Yovel said. The brains of the bats actually transformed echoes into visual images, he explained.
“We have shown that bats are able to translate the acoustic echoes of some objects into visual representations. We next hope to harness this new echo-to-image paradigm to examine whether bats can build a 3D representation of the world based on echoes alone.
“Bats are useful models for studying this and other related phenomena because of their dual reliance on two remote sensory systems: vision and echolocation,” Yovel added.