Image of fish movements in a tank
The fish hovered within a tube where they wiggled back and forth constantly to maintain a steady level of sensory input about their surroundings. (Credit: Johns Hopkins University)

The constant movement of fish that seems random is actually precisely deployed to provide them at any moment with the best sensory feedback they need any to navigate the world, researchers found. The finding enhances our understanding of active sensing behaviors performed by all animals including humans, such as whisking, touching and sniffing, and demonstrates how robots built with better sensors could interact with their environment smarter and more effectively.

For humans, active sensing is when we feel around in the dark for the bathroom light switch, or when we bobble an object up and down in our hands to figure out how much it weighs. We do these things almost unconsciously, and scientists have known little about how and why we adjust our movements according the sensory feedback we get from them.

To answer the question, they studied weakly electric fish, fish that generate a weak electric field that emanates around their body and helps them with communication and navigation. The team created an augmented reality for the fish so they could observe how a fish’s movements changed as their feedback from the environment changed.

Inside the tank, the fish hovered within a tube where they wiggled back and forth constantly to maintain a steady level of sensory input about their surroundings. First, the researchers changed the environment by moving the tube in a way that was synchronized with the fish’s movement, making it harder for the fish to extract the same amount of information. Next they made the tube move in the opposite direction of the fish, making it easier for the fish. In each case, the fish immediately increased or decreased their swimming to get the same information. They swam harder when the tube’s movement gave them less sensory feedback and they swam less when they could get could get more feedback from with less effort. The findings were even more pronounced in the dark when the fish had to lean more on their electrosense.

They hope the biological insight can be used to build robots with smarter sensors. Sensors are rarely a key part of robot design now but these findings made Cowan realize they perhaps should be.

A video observing the fish movements can be viewed at https://www.youtube.com/watch?time_continue=3&v=GqPtNTwxsqc.

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