Jumping spider uses fuzzy eyesight to judge distance

January 27, 2012 by Lin Edwards, Phys.org report

Anterior view of the jumping spider, Hasarius adansoni. A pair of principal eyes is located at the anteromedial area of the body, lying between two lateral eyes. Image © Science/AAAS
(PhysOrg.com) -- One of the ways in which humans determine distance is by estimating the sharpness of an image—closer objects produce a sharp image, while those further away are out of focus. For us, this is a minor additional method of judging distance, but now scientists in Japan have for the first time found an animal that appears to use this method as its primary means of depth perception.

Adanson’s (Hasarius adansoni) captures prey by jumping from a distance. The question that has puzzled scientists is, how do their eyes allow them to perceive depth? Their front eyes do not give them the two distinct but overlapping views needed for binocular vision, used by humans. They also do not use the motion parallax many insects use, since their head remains motionless when they are about to jump. (Motion parallax is a system in which the animal moves its head from side to side so that close objects move further across the field of view than those further away.) Now the new study reveals that the spiders use an image defocus system to enable them to judge distances.

Adanson’s jumping spider has excellent eyesight, provided by eight eyes: a pair of primary eyes (large and at the front), two anterior lateral eyes, one at either side of the primary eyes and also facing forward, and two smaller pairs of eyes on the top of their heads, one of which is almost undetectable by the naked .

The research team, led by Takashi Nagata, from Osaka City University, blocked the anterior lateral pair of eyes of the jumping spider and found that they use this smaller pair of eyes to detect motion, but blocking their vision had no effect on the spider’s ability to judge distance.

It has been known since the 1980s that the retinas in the principal eyes in jumping spiders have a unique structure that is shaped like a staircase, and they contain four layers of photoreceptors rather than one layer, as human eyes have. The new study revealed that the two deeper retinal layers contain pigments sensitive to green light and the two layers closest to the surface contain pigments sensitive to ultraviolet light. Of the two layers most sensitive to green light, only the deepest receives focused images, and the other receives an out of focus image.

To test the idea that the spiders could judge depth from the amount of defocus in the second green pigment layer, the researchers placed spiders one at a time in a container, along with some fruit flies and then tested their ability to catch the flies under red and green lights.

The results showed that green light was necessary for accuracy since the spiders were able to judge their jumps successfully in green light, but often misjudged in red light (which does not contain the shorter wavelength green light). The researchers also created a mathematical model to predict how far off the jumps would be under different wavelengths of light, and found that the model did accurately predict the spiders’ performance.

The researchers concluded that the spiders were indeed using the extent of defocus in the second green pigment layer of the retina to judge distance, and they are the only known animals to use this system as their primary means of . Since other jumping spiders have the same type of retina, they may also use the same method.

In a paper published in the journal Science, the researchers conclude that further study of the vision system used by jumping is necessary and that it could have applications in robotic and other computer vision systems.

Explore further: The eyes have it for perfect predator

More information: Depth Perception from Image Defocus in a Jumping Spider, Science 27 January 2012: Vol. 335 no. 6067 pp. 469-471. DOI:10.1126/science.1211667

The principal eyes of jumping spiders have a unique retina with four tiered photoreceptor layers, on each of which light of different wavelengths is focused by a lens with appreciable chromatic aberration. We found that all photoreceptors in both the deepest and second-deepest layers contain a green-sensitive visual pigment, although green light is only focused on the deepest layer. This mismatch indicates that the second-deepest layer always receives defocused images, which contain depth information of the scene in optical theory. Behavioral experiments revealed that depth perception in the spider was affected by the wavelength of the illuminating light, which affects the amount of defocus in the images resulting from chromatic aberration. Therefore, we propose a depth perception mechanism based on how much the retinal image is defocused.

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1 / 5 (5) Jan 27, 2012
Really? I thought they used sonar.
2.4 / 5 (5) Jan 27, 2012
Spiders are unique between other insects with the fact, they're not using composite eyes like fast moving dragonfly or lurking mantis, for example. It's interesting example of convergence of evolution. Why they're using just the way of seeing common for much advanced animals? Just for to appear more cutely?
not rated yet Jan 27, 2012
Rawa1, Wow, a picture of the rare jumping passerby spider. It has evolved a very uncommon method of entrapping it's prey. Looking just like a passer-by going about it's day, it approaches it's victims and asks them if they have the time, and while they are looking at their watch it bites their head off.
Espicially effective against centipedes, who can never remember which leg they put their watch on that morning.
3.7 / 5 (3) Jan 27, 2012
Spiders are unique between other insects

That's because spiders aren't insects. They're arachnids.
Same phylum (arthropod), different class.
1 / 5 (1) Jan 27, 2012
It still doesn't explain the original problem

2.3 / 5 (3) Jan 28, 2012
Kind of strange that it has 4 forward facing eyes and it isn't using binocular vision. Most animals develop forward facing eyes specifically for that reason.
1 / 5 (1) Jan 28, 2012
Maybe the insect uses compound eyes, because it requires smaller brain to process distributed image with distributed neural network... And it can use the hyperdimensional information like the polarization of light for additional tricks (vision behind the corners, etc).
2 / 5 (2) Jan 28, 2012
Kind of strange that it has 4 forward facing eyes and it isn't using binocular vision. Most animals develop forward facing eyes specifically for that reason.

Binocular vision requires that the eyes are parted by a significant distance.

Our eyes are some inches apart, and we see depth that way up to maybe ten yards. After that it becomes increasingly inaccurate to judge distances that way, because the angular resolution of the eye is roughly 1/60th of a degree and the differences in the two images become too small to notice.

The spider's eyes are millimeters apart, which makes binocular vision ineffective beyond an inch or so. It may see with stereo vision, but only in the near field.
1.5 / 5 (2) Jan 28, 2012
Mind, the accuracy of stereo vision also depends on the accuracy of the muscles to turn the eyes. Otherwise the brain can't tell what it's supposed to be seeing and how the images are supposed to be offset from one another. If one eye drifts slightly and the brain doesn't notice it, the depth perception becomes misleading.

The jumping spider can't turn its eyes. It can move the retina about a little instead, but the lens is fixed.
1 / 5 (1) Jan 31, 2012
The spider's worse scores without green light is not sufficient to exclude binocular vision in estimating distances. It only demonstrates that the other color retinas are less, or not at all, used for distances. (Humans don't use any color cells for distance estimation, only the black-and-white ones.)

For example, the spider may use blur differences between the green retinas for very short distances, where binocular vision without turning eyes would require extensive neural networks a small spider can't afford. At longer distances, blur becomes a very inaccurate method. Stereo vision should be very usable between 2 to a dozen inches.

Ability to turn the eyes is not needed for stereo vision. (You know where nearby objects are even while looking at a distant mountaintop.) Nature doesn't support useless body parts, so, without stereo vision, the spider would have one bigger eye instead, like the octopus.

What biology needs, is due diligence, attention, and thinking.
1 / 5 (1) Jan 31, 2012
Wikipedia/Jumping_spider is a good article to read here. And there is a link to www.cogs.susx.ac.uk /ccnr/Papers/Downloads/Harland_Cimb2000.pdf which is a 10-page paper written in 2000 on their eyesight. Mr. Nagata's team obviously didn't bother reading it. Turns out the spider uses the stepped design of the fourth principal-eye retina for very accurate distance measurement. (Although Figure 4 is not consistent with the detailed explanation.)

An illustration on the Wikipedia page seems to show that the principal eyes do not have overlapping vision, which does exclude stereoscopic vision. However, the small front eyes do overlap. Considering the fields of the other small eyes reach each other exactly and without overlap, this frontal overlap has to be "on purpose", which would indicate coarse-grain and quick stereoscopy. (This is not studied in either paper.)
1 / 5 (1) Jan 31, 2012
And finally, here's some Real Science about jumping spiders: http://peckhamia....83.1.pdf

Chapter 4 (pp. 13-18) describes jumping spider vision. In essence, the small front eyes are used for stereoscopic vision and distance measurement, and the large front eyes are used as telescopes, and can look in independent directions, a little like a chameleon's eyes.

After all this, I feel Mr. Nagata is both sloppy and ignorant.

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