Jumping Spiders see clearly by blurring their vision

Researchers in Japan have now discovered that the arachnids accurately sense distances by comparing a blurry version of an image with a clear one, a method called image defocus.
Jumping spiders, which hunt by pouncing on their prey, gauge distances to their unsuspecting meals in a way that appears to be unique in the animal kingdom, a new study finds.
There are several different visual systems that organisms use to accurately and reliably judge distance and depth. Humans, for example, have binocular stereovision. Because our eyes are spaced apart, they receive visual information from different angles, which our brains use to automatically triangulate distances. Other animals, such as insects, adjust the focal length of the lenses in their eyes, or move their heads side to side to create an effect called motion parallax — nearer objects will move across their field of vision more quickly than objects farther away.
However, jumping spiders (Hasarius adansoni) lack any kind of focal adjustment system, have eyes that are too close together for binocular stereovision and don’t appear to use motion parallax while hunting. So how are these creatures able to perceive depth?
Researchers in Japan have now discovered that the arachnids accurately sense distances by comparing a blurry version of an image with a clear one, a method called image defocus.
Jumping spiders have four eyes densely packed in a row: two large principal eyes and two small lateral eyes. The spider uses
its lateral eyes to sense the motion of an object, such as a fly, which it then zeros in on using its principal eyes, Akihisa Terakita, a biologist at Osaka City University in Japan and lead author of the new study, explained in an email to LiveScience.