The constant, seemingly random, movement of fish is actually gives them the best sensory feedback they can get to navigate the world, say Johns Hopkins University researchers.
The finding enhances our understanding of the sensing behaviours of all animals, including humans, such as whisking, touching and sniffing. It shows how building robots with better sensors would let them interact with their environment more cleverly and efficiently.
“You have to actively move to perceive your world but what we found that wasn’t known before is that animals constantly regulate these movements to optimize sensory input” says Noah Cowan, a roboticist at Johns Hopkins and senior author of the research.
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, Cowan and his colleagues 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.
“Their actions to perceive their world is under constant regulation,” said Eric Fortune from the New Jersey Institute of Technology, a co-author on the study. “We think that’s also true for humans.”
“Surprisingly engineers don’t typically design systems to operate this way,” says Debojyoti Biswas, the lead author. “Knowing more about how these tiny movements work might offer new design strategies for our smart devices to sense the world.”
Closed-Loop Control of Active Sensing Movements Regulates Sensory Slip. Debojyoti Biswas, Luke A. Arend, Sarah A. Stamper, Balázs P. Vágvölgyi, Eric S. Fortune, Noah J. Cowan. Current Biology, Vol. 28, Issue 24, p4029–4036.e4