I was cruising io9 today, and I came across this story.
If you don’t have time to read the story, but want me to summarize this for you, here we go. Jumping spiders, which are terrifyingly awesome, have a strange problem. They have eight eyes and use those eyes to judge distance, but we didn’t understand the mechanism that they used to judge those distances.
Eyes are super interesting. Humans think of eyes as the windows to the world. We use seeing and understanding interchangeably. So, when we see things that have compound eyes or multiple eyes, it kind of freaks us out. Check out that spider up there. Or go outside with and LED and hold it as close to your eye level as possible. You’ll see this, if there are spiders about.
We didn’t understand how the jumping spider judged distances until recently. Apparently, they have four layers of retina. The retina is where the focused images is projected, where it is translated into nerve cells, and ends up in the brain. Human beings have three layers in the retina. Our three layers are rods, cones and nerves. Rods perceive black and white. Cones perceive color. Nerves take the information from the rods and cones to the brain. The jumping spider adds a fourth later, which is purposely out of focus, that perceives green.
What this green perceptive layer does is causes the prey to be in sharp relief to the background of green. The focus allows the jumping spider to accurately judge distances. By using red and green light and observing the jumping spiders, they found that this green perception gave them their accurate distance perception.
Anyway, you should be interested, because now we’re going to get distance viewfinders based on this principle. It’s just cool research.