Stereopsis in animals: evolution, function and mechanisms

Abstract

Stereopsis is the computation of depth information from views acquired simultaneously from different points in space. For many years, stereopsis was thought to be confined to primates and other mammals with front-facing eyes. However, stereopsis has now been demonstrated in many other animals, including lateral-eyed prey mammals, birds, amphibians and invertebrates. The diversity of animals known to have stereo vision allows us to begin to investigate ideas about its evolution and the underlying selective pressures in different animals. It also further prompts the question of whether all animals have evolved essentially the same algorithms to implement stereopsis. If so, this must be the best way to do stereo vision, and should be implemented by engineers in machine stereopsis. Conversely, if animals have evolved a range of stereo algorithms in response to different pressures, that could inspire novel forms of machine stereopsis appropriate for distinct environments, tasks or constraints. As a first step towards addressing these ideas, we here review our current knowledge of stereo vision in animals, with a view towards outlining common principles about the evolution, function and mechanisms of stereo vision across the animal kingdom. We conclude by outlining avenues for future work, including research into possible new mechanisms of stereo vision, with implications for machine vision and the role of stereopsis in the evolution of camouflage.

Binocular disparity can augment the capacity of vision without affecting subjective experience of depth

“…We used the most complex random-effect structure with which the model still converged. Because enumeration data is known to contain a breakpoint around number 2-4, the data was fitted with two-segment linear models in addition to standard one segment models (for formal description, see 29). We fitted three alternative two-segment models where the length of the first segment ranged numbers 1 –2, 1 –3, or 1 –4.…”

“…We asked participants to enumerate objects in briefly presented naturalistic (Experiment 1) and artificial (Experiment 2) scenes in immersive virtual reality. This type of enumeration task yields well-documented capacity limits where up to 3-4 items can be enumerated rapidly and accurately, known as subitizing. Our results show that although binocular disparity did not yield a large general improvement in enumeration accuracy or reaction times, it improved participants’ ability to process the items right after the limit of perceptual capacity.…”

“…Humans and many other animals have two forward facing eyes and a large overlap between their visual fields 1. One of the major benefits of this is stereopsis: integration of the slightly different viewpoints of the two eyes (binocular disparity) results in tangible subjective sensation of three-dimensional visual space, and accurate coding of depth 2,3,4. Binocular disparity improves eye-hand coordination 5,6,7, and visual recognition of singular items when simple stimulus displays are used 8,9,10,11.…”

The visual social environment affects non-additively neighbor spacing and interaction time in zebrafish

“…However, distance can complicate this assessment, as objects that are far away have a reduced visual angle and consequently appear smaller than they really are. To compensate for this, animals have evolved various mechanisms to improve depth perception (Howard 2012;Nityananda and Read 2017), ultimately allowing them to establish size constancy (i.e. ability to perceive the relative size of an object independent of its angular size; Douglas et al, 1988;Frech et al, 2012;Zeil, 2000).…”

Motion-in-depth perception and prey capture in the praying mantis

“…Several cues could enable the perception of depth. These include cues provided by 46 motion, such as optic flow or motion parallax, pictorial cues (such as shading and relative size) 47 and stereoscopic cues (Nityananda and Read, 2017). The latter involve cues that convey depth 48 as a result of comparing the differential visual input and scenes perceived by the two eyes.…”