Each eye moves in a different direction, depending on the change in the animal’s head position. An analysis of both eyes’ field of view found that the eye movements exclude the possibility that rats fuse the visual information into a single image like humans do.
Instead, the eyes move in such a way that enables the space above them to be permanently in view — presumably an adaptation to help them deal with the major threat from predatory birds that rodents face in their natural environment, an institute release says.
Like many mammals, rats have their eyes on the sides of their heads. This gives them a very wide visual field, useful when detecting predators. However, three-dimensional vision requires overlap of the visual fields of the two eyes. Thus, the visual system of these animals needs to meet two conflicting demands at the same time; on the one hand maximum surveillance and on the other hand detailed binocular vision.
The research team fitted minuscule cameras weighing only about one gram to the animals’ heads, which could record the lightning-fast eye movements with great precision. The scientists also measured the position and direction of the head, enabling them to reconstruct the rats’ exact line of view at any given time.
The Max Planck scientists were surprised by their findings. Although rats process visual information from their eyes through very similar brain pathways to other mammals, their eyes evidently move in a totally different way.