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Why do cats have vertical pupils? - Emma Bryce

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Peering into the eyes of different animals, you’ll see some extraordinarily shaped pupils. House cats, for one, are twilight hunters with vertically elongated pupils. Many grazing animals, like goats, have rectangular pupils. Other animals have crescent- or heart-shaped pupils. So, what’s going on? Why are there so many different pupil shapes? Emma Bryce digs into the science of animal vision.

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TED-Ed Animations feature the words and ideas of educators brought to life by professional animators. Are you an educator or animator interested in creating a TED-Ed Animation? Nominate yourself here »

Meet The Creators

  • Educator Emma Bryce
  • Director Bálint Gelley, CUB Animation Ltd.
  • Narrator Alexandra Panzer
  • Storyboard Artist Daniel Gray
  • Animator Iván Tamás
  • Compositor Iván Tamás
  • Art Director Barbara Bakos
  • Music József Iszlai
  • Sound Designer József Iszlai
  • Director of Production Gerta Xhelo
  • Editorial Director Alex Rosenthal
  • Producer Bethany Cutmore-Scott
  • Script Producer Cella Wright
  • Special Thanks Martin S. Banks
Additional Resources for you to Explore
Let’s take a deeper look... at the pupil! As a starting point, why not visit this brief guide that introduces you to all the key parts of the eye and how they function. Another provides a useful graphic on the full anatomy of the eye. As for the pupil, this article provides some insights into the role of this mysterious black void. Our TED-Ed video also touches on the fact that pupils can change size depending on our emotional states. But why? This article reveals some fascinating clues.

As we now know, pupils can differ vastly in shape, size, and function. In 2015, a group of researchers endeavored to find out why, and their work provided many of the answers we explore in this video. Their fascinating research is published in the journal Science which makes for an interesting read! It’s not an especially light read, however: you might prefer this article, where the researchers provide a very clear, easy-to-digest summary of their work, exploring the differences in pupil shapes between cats, sheep, and wolves. Need a break from reading? Then try this podcast, where researcher Martin Banks explains the variable pupils of the animal world.

In fact, he and his colleagues discovered that grazing animals rotate their eyeballs when they move their heads to align their pupils with the horizon, a phenomenon known as ‘cyclovergence.' This intriguing video explains that phenomenon, with the bonus that you get to see it in action!

If you’re interested in reading more about animals’ differently shaped pupils, and the scientists’ research, then why not take a look at these popular science articles: one specifically on the cat’s slit-pupiled vision; or this one on the general differences between animal pupils. Or, have a quick look at this short explanatory National Geographic video which features some insights on animal vision from biologist Tom Cronin. This scientific blog post digs into the key differences between vision generated by different pupil shapes, what it has to do with depth perception, and how that shapes vision in our round-pupiled, human eyes. In addition, this study digs into the phenomenon of pseudopupils that had us fooled, while this science article touches on its puzzling appearance in the complex compound eyes of the praying mantis.

Yet, when it comes to animal vision, there’s still much more we don’t know than what we do, with many pupil shapes still presenting a puzzle. If you’re curious, why not read more about the mysterious ‘U’ and ‘W’-shaped pupils that belong to the cephalopods, including those belonging to our video’s final starring act, the cuttlefish. In fact, their pupils are so fascinating that there’s a whole research study devoted to them (and here’s a source that explains some of the basic principles of cuttlefish vision).

Beyond the pupil, there are still many wonders to uncover about the eye, especially our human ones. Why not broaden your knowledge and take a look at this TED talk that delves into the evolution of the eye, or this TED-Ed video looking at what cameras can teach us about our vision. Or, how about this talk that explores a prevailing mystery that many of us will be familiar with: what on earth are those weird floaters that drift across your vision from time to time?

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About TED-Ed Animations

TED-Ed Animations feature the words and ideas of educators brought to life by professional animators. Are you an educator or animator interested in creating a TED-Ed Animation? Nominate yourself here »

Meet The Creators

  • Educator Emma Bryce
  • Director Bálint Gelley, CUB Animation Ltd.
  • Narrator Alexandra Panzer
  • Storyboard Artist Daniel Gray
  • Animator Iván Tamás
  • Compositor Iván Tamás
  • Art Director Barbara Bakos
  • Music József Iszlai
  • Sound Designer József Iszlai
  • Director of Production Gerta Xhelo
  • Editorial Director Alex Rosenthal
  • Producer Bethany Cutmore-Scott
  • Script Producer Cella Wright
  • Special Thanks Martin S. Banks

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