Researchers have found that jumping spider (Hasarius adansoni) uses blurring images as a primary means of depth perception by using green color light.
This research has been done by researchers in Japan and published online in the January 27 issue of the journal Science.
Every organism uses different visual systems to check for the distance accurately and reliably such as humans have binocular stereovision. Our eyes are spaced apart and get images from different angles, the distances of which are automatically triangulated by our brain. However, jumping spiders lack this binocular stereovision.
Researchers have found that the arachnids (eight-legged organisms) observe distances by comparing the blurry vision of an image with a clear one, which is known as image defocus.
Jumping spiders have four eyes, i.e. two large principal eyes and two small lateral eyes, closely placed together in a row. The spider uses it lateral eyes to detect the motion of an object. Retinas in the spider’s principal eyes have four distinct photoreceptor layers. Researchers have found that the two layers near the surface contain ultraviolet-sensitive pigments while the deeper layers have green-sensitive pigments.
Researchers have suggested that as a result of layers’ respective distances from the lens of the eye, incoming green light is focused only in the deeper layer while the other green-sensitive retinal layer receives defocused images. Spiders may get depth cues from the amount of defocus in the fuzzy layer that is proportional to the distance of the object from the lens of the eye.
In order to check this hypothesis, researchers placed the spider along with three to six fruit flies in a cylindrical plastic chamber placed in a white styrene foam box. Researches then placed them in different lights of red and green, and found that the spiders were more capable to catch the flies in green light.
Takashi Nagata, Mitsumasa Koyanagi, Hisao Tsukamoto, Shinjiro Saeki, Kunio Isono, Yoshinori Shichida, Fumio Tokunaga, Michiyo Kinoshita, Kentaro Arikawa, Akihisa Terakita, (2012). Depth Perception from Image Defocus in a Jumping Spider. Science, DOI: 10.1126/science.1211667