Look at the animals. What do you notice about where their eyes are compared to ours?
We are going to measure how that difference affects how they can see compared to us.
Visual field test:
Look at other animals' eyes. Where are they?
Our eyes are just on the front of our head, so we can't see as far behind us.
Work with a partner to see how far behind us we can see: partner holds their finger behind your head, then slowly moves it around the side of your head. Tell them when you see the finger. Then switch over.
Our visual field is about 200 degrees.
Herbivores have 350 degrees. They can almost see behind their head.
So what good are two eyes on the front of the head?
They let us see how far away something is - depth perception.
Try putting your fingers to the side, then slowly bring together to meet in front of you. Now try with one eye closed. (see notes)
For most of their visual field, horses can only see with one eye.
They do have binocular vision for a small part of their visual field (65 degrees right infront of their face) and may hold their heads up to see something infront of them.
Herbivores are eaten by other animals, so need to be able to look out for predators, so it is worth not having some binocular vision to see all around them.
Humans hunt other animals - they are predators. They need to accurately spot and catch prey. Stereo vision most useful adaption.
Herbivores can only use binocular vision by looking straight at an object, raising its head. It does it when it looks at a distant predator or focuses on an obstacle to jump. To use binocular vision on a closer object near the ground, such as a snake or threat to its feet, a herbivore e.g. horse drops its nose and looks downward with neck somewhat arched.
The different eye arrangements are an adaptation for each animal's environment.