The study was published in the Science Advances journal and was undertaken by a mixed team of University of California and the UK’s Durham University research lead by visual scientist Dr. Martin S. Banks. The hypothesis, which was heavily questioned afterwards by other visual scientists, is that species which have vertical and circular pupils got them because they help in hunting, while those with horizontal pupils had them because it helped them spot predators.
The research included 214 species, and was done by using computer models to simulate animal vision. It found out the fact that pupil shape actually determines how much light does the animal’s vision capture in certain directions: for example, animals with horizontal pupils sacrifice a little bit of their field of view below and above the eye to gain better peripheral view, which is crucial to spotting potential predators lurking around.
It also observed that, in the case of sheep, they rotate their eyes up to 50 per cent when tilting their head down to eat, so that they could keep their pupils parallel to the ground and keep their awesome peripheral vision. The same result was also observed in the case of horses and other grass grazing animals such as goats and deer.
After identifying this, Dr. Banks and his team simulated the behavior of eyes with vertical pupils and observed that this also has its own unique perk: it makes the predator accurately estimate distance to its prey by focusing on it and sharpening its depth-based perception, so that allows it then to calculate whether it can catch it or if it needs to prowl closer. Cats and alligators are amongst those that have vertical sliced pupils.
An exception to this was provided by particularly large predators, such as tigers or lions, who had neither horizontal, nor vertical but round pupils. The exception in this case was explained by the fact that those animal had a height advantage which gave them a better field of view and line of sight on its own, so their eyes didn’t had to adjust as drastically to their condition.
The results have been received with mixed feelings by biologists and vision scientists. While some argued that a computer simulation cannot exactly account for the entire role of the eye in animals, and noted several unexplainable exceptions to this rule, others praised the rotating eyes finding.
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