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Basic arrangement of spider eyes, viewed from above. Most spiders have eight eyes, which tend to be arranged into two rows of four eyes on the head region. The eyes can be categorised by their location and are divided into the anterior median eyes (AME), anterior lateral eyes (ALE), posterior median eyes (PME), and posterior lateral eyes (PLE).
The distance between the two eyes on an adult is almost always 6.5 cm and that is the same distance in shift of an image when viewing with only one eye. [17] Retinal disparity is the separation between objects as seen by the left eye and the right eye and helps to provide depth perception. [17]
Depth sensation is the corresponding term for non-human animals, since although it is known that they can sense the distance of an object, it is not known whether they perceive it in the same way that humans do. [1] Depth perception arises from a variety of depth cues. These are typically classified into binocular cues and monocular cues ...
Now, a Harvard team has created a more efficient depth sensor by taking cues from jumping spiders, which can pounce several times the length of their bodies to land on unsuspecting flies.
Spiders do not have compound eyes, but instead have several pairs of simple eyes with each pair adapted for a specific task or tasks. The principal and secondary eyes in spiders are arranged in four, or occasionally fewer, pairs. Only the principal eyes have moveable retinas. The secondary eyes have a reflector at the back of the eyes.
As the eyes are too close together to allow depth perception, and the animals do not make use of motion parallax, they have instead evolved a method called image defocus. Of the four photoreceptor layers in the retina, the two closest to the surface contain a UV-sensitive opsin (visual pigment), while the two deepest contain a green-sensitive ...
While binocular disparities are naturally present when viewing a real three-dimensional scene with two eyes, they can also be simulated by artificially presenting two different images separately to each eye using a method called stereoscopy. The perception of depth in such cases is also referred to as "stereoscopic depth". [1]
The tip of the tarsus bears claws, which vary in number and size. Spiders that spin webs typically have three claws, the middle one being small; hunting spiders typically have only two claws. Since they do not have antennae, spiders use specialised and sensitive setae on their legs to pick up scent, sounds, vibrations and air currents. [6]