"These fish are ideal both because we can easily monitor the sensing signals that their brains use and because the task we asked the fish to do -- swim forward and backward inside a small tube -- is very simple and straightforward," said Fortune, who also uses the fish to study the neural basis and evolution of behavior.
The fish prefer to "hide" inside these tubes, which are immersed in larger water tanks. In their research, Cowan and Fortune challenged the fish's ability to remain hidden by shifting the tubes forward and backward at varying frequencies. This required the fish to swim back and forth more and more rapidly in order to remain inside the tubes. But as the frequency became higher, the fish gradually failed to keep up with the movement of the tubes.
The team's detailed engineering analysis of the fish's adjustments under these conditions suggested that the animal's sensors and brains are "tuned" to consider Newton's laws of motion, Cowan said. In other words, the team found that the fish's nervous systems measured velocity, so the fish could accelerate or "brake" at just the right rate to remain within the moving tube.
"The fish were able to accelerate, brake and reverse direction based on a cascade of adjustments made through their sensory and nervous systems, in the same way that a driver approaching a red light knows he has to apply the brakes ahead of time to avoid overshooting and ending up in the middle of a busy intersection," Fortune said. "Your brain has to do this all the time when controlling movement because your body and limbs, like a car, have mass. This is true for large motions that require planning, such as driving a car, but also for unconscious control of all movements, such as reaching for a cup of coffee. Without this sort of predictive control, your hand would knock the cup off the table every time."