Spider Sight! Humans perceive depth using binocular vision, used to advantage in 3D movies that relay slightly different images to each eye. Since insects do not have widely spaced eyes as we do, they move their heads side to side and use motion parallax to gauge depth.
Jumping spiders can execute remarkably precise jumps over gaps to catch their prey, but use neither of these techniques. They not only have enlarged main eyes that give them visual acuity, but also two or three pairs of secondary eyes. Their eyes have not just one layer of retina, but multiple layers. The way they perceive depth is by an unusual method of fuzzy logic. While the first layer focuses image sharply, the light falling on the second layer gives a fuzzy image. The amount of defocus in this second layer gives them a clue to depth. Both layers are tuned primarily to green light. When spiders were shown flies bathed in green light, they were able to capture them accurately. However, if green light was missing from the spectrum, they consistently missed their jumps.
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Thanks to Huffington Post Science for covering the story: http://www.huffingtonpost.com/2012/01/26/jumping-spider_n_1234873.html?ref=science#s643107
Perspective article in Science 27 January 2012: Vol.335 no. 6067 pp. 409-410 DOI:10.1126/science.1216887
Photo Credit: Alex Wild http://www.alexanderwild.com/
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A late submission to #spidersunday curated by Chris Mallory!
madame scientist's not-so-mad musings 
Wow Very Very Exccelent N You are online
What a cutie!
And, as is all your posts, fascinating look into how vision works for other species!
Funniest spider pic, especially with those hairs sticking out, Gregory Esau . I will admit to coming up with the short blurb after I fell for this spider.
How many eyes does this spider has, Ma’am?
I did not know about the green light !!
Thank you for sharing this info 🙂
Hey, Sanjeev Kumar ..great question! According to Wiki, “All jumping spiders have four pairs of eyes with very large anterior median eyes.” Picture and more info here: http://en.wikipedia.org/wiki/Jumping_spider
Christiane Cantin , the Science paper tested various wavelengths. Apparently, 2 of 4 retinal layers are tuned to green light and the other two to ultraviolet wavelengths.
Wow, how soon until this technique is used in 3D gaming, then robotics (yes, it seems that is the order these advances come 🙂
Hudson Ansley For his college course a friend of mine built a machine vision system that used one camera. His system relied on some awesome math to make a good guess about depth from the captured frames.
In a later conversation we discussed scanning a target with cone of light that had a known focus angle and guessing depth from the size of the circle that was reflected back. This scheme is kind of an inverted form of what our beautiful arachnid friend above uses. If it hasn’t already been done I think a crude demonstration could be hacked together with a Wiimote and some IR LEDs.
at last…
https://plus.google.com/u/0/116785137310232468049/posts/RT5VQEv24Kj
( :
I remember that post, Konstantin Makov ! 🙂
Quite remarkable, the ways which different species have evolved to accomplish depth perception!
Thanks Rajini…once again a superb front view of jumping spider… just mesmerizing!
Thank you so much for the insight, Ma’am. I had no idea that spiders had so many eyes, and with the ability to differentiate UV lights. Thanks Rajini Rao
I am not a scientist so what I am going to say is only my opinion with not proof:-)
I think humans do four methods (if not more)-
1. Binocular vision as you describe
2. We also move our head or some cases tilt it to get parallax.
3. I use the focus method for short distances up to say few meters. I know this because when I paint a canvas I often try to gauge the defocus to create depth of field.
4. Humans use sound phase method for direction and distance within few meters (phase diff bet the sound waves into two ears) to augment the depth if the possible.
You’re right, mandar khadilkar . Humans use a whole range of techniques to perceive depth. In addition to the methods you mention, we use all forms of visual perspectives..kinetic, curvilinear, texture/shading and so on to gauge depth. I was astonished that even the process of accommodation..when the muscles holding our lens stretch or contract to bring an image into focus, is interpreted by our brain to inform on depth. Pretty cool, right?
So here is something really cool about human vision: my miserable eyesight is corrected by “monovision” which means that the contact lens in one eye corrects for distance viewing (short sight) and the other corrects for reading (long sight). Apparently my brain can seamlessly integrate the different signals so that I can see perfectly well. I’m told that some people can’t tolerate this, but it works just fine for me 🙂
Creepy.!
http://blogs.scientificamerican.com/observations/2012/01/26/jumping-spiders-use-blurry-vision-to-catch-quick-prey-with-precision-video/ seee : ))
Awesome find, alev uneri , thanks! The video is short and amazing..definitely recommend watching it.
you’re welcome : )
Looking into those eyes you can tell that it’s thinking
+Rajiji Rao – Thanks for additional info. After your more detailed info, I realized how many ways we estimate the depth. Not just depth but the whole spacial dimensions are in our brain as estimates with constant adjustments.
We constantly try to make sense of the inputs we are getting and creating a virtual world inside our brain.
I just remember how we get confused by the perspective vision/images. Our understanding of depth/size is so linked. Full moon does not look the same size and at the same distance every time.
Visibility affects our estimation of distance i.e. hills look closer when it is very clear.
Very true..nice that the cute spider pix is getting us to think about the complexity of vision 🙂
Shinae Nae Since they turn towards interesting things like e.g. cameras, they are always cute (unless you use two cameras) 😉
He oddly looks like a Koala Bear.
you know, you are right…. how funny is this??..
nice
nice
I ♥ this pic!