Insights from wriggling fish may improve robot design

Constant and seemingly random movement of fish serves to optimise their sensory feedback, which may enhance the way sensors are deployed in robot design

One characteristic of any large group of animals IS they seem to move constantly and almost at random. It is particularly pronounced when observing a large number of fish; they flicker and wriggle in a constant blur of sparkling scales. Researchers at Johns Hopkins University have found that these movements are in fact not random at all, but serve to maximise what the fish can extract from their environment, a finding that the researchers believe may have profound implications for robot design.

robot design fish
The constant flickering movement in a school of fish is a deliberate strategy to optimise each individual fishes’ sensory input. Author: Gordon Firestein via Wikimedia Commons.

Mechanical engineer and roboticist Noah Cowan, who led the study, explains that it was already known that all animals have to actively move in order to sense their environment. “There’s a saying in biology that when the world is still, you stop being able to sense it,” he said. To test how this worked, he and his colleagues, including researchers from the New Jersey Institute of Technology (NJIT), studied fish that generate a weak electric field around their bodies, which is believed to help them sense their environment and communicate with each other.

The study involved watching how the fish moved inside a transparent tube submerged in a tank. When the tube was kept still, the fish constantly wriggled back and forth. To challenge the fishes’ senses, the team moved the tube in two ways: synchronised with and opposite to the animals’ movement. When the tube’s movement gave them less sensory feedback – that is, when it was moving synchronised with them – they swam farther, and when moving opposite to them they swam less. In the dark, when the fishes’ electric senses were the only way they could receive any feedback on their environment, their movements were even more pronounced.

“What we found that wasn’t known before is animals constantly regulate these movements to optimise sensory input,” said Cowan. “The action to perceive the world is under constant regulation,” added Eric Fortune from NJIT. “We think that’s also true for humans.” One example of how humans use movement to optimise sensory input is moving our hands up and down to estimate the weight of an object we are holding, the team speculates in a paper in Current Biology describing their research.

The lead author on the study, Debojyoti Biswas, notes that engineers do not take account of the importance of active movement to optimise sensory input when designing the placement of sensors on robots, but understanding how this can improve information-gathering about the environment could help improve robot design. “Knowing more about how these tiny movements work might offer new design strategies for our smart devices to sense the world,” he said.