Rats Always have a View of the Sky in their Vision

Rats' eyes move in such a way that they always have a clear view of the sky, a new study has found. Researchers say that this adaptation helps the rats monitor their environment for any potential predators.

The research on rats' vision was carried out by scientists at the Max Planck Institute for Biological Cybernetics in Tübingen. The study team used miniaturized high-speed cameras and high-speed behavioral tracking to assess how rats see the world around them. The team found that when rats are running around, their eyes move in opposite directions, both horizontally and vertically.

The study found that rats don't have a single vision like humans; instead they have an additional view of the sky.

"Humans move their eyes in a very stereotypical way for both counteracting head movements and searching around. Both our eyes move together and always follow the same object. In rats, on the other hand, the eyes generally move in opposite directions," explained Jason Kerr from the Max Planck Institute for Biological Cybernetics.

In humans, deviation of even less than one degree from the field of view results in double vision. Researchers found that in rats, this deviation is 40 degrees in horizontal plane and about 60 degrees in vertical plane. This large deviation means that no matter where the rats are looking, they can always see what's happening above their heads.

For the study, researchers attached tiny cameras that weight less than a gram to the rats' head. The cameras had the ability to record fast movements with great precision. The researchers also tracked the rats' vision field.

Through various behavioral experiments, researchers found that rats' eye movement depends on the way the head is positioned.

"When the head points downward, the eyes move back, away from the tip of the nose. When the rat lifts its head, the eyes look forward: cross-eyed, so to speak. If the animal puts its head on one side, the eye on the lower side moves up and the other eye moves down." said Jason Kerr in a news release.

The study "Rats maintain an overhead binocular field at the expense of constant fusion" is published in the journal Nature.