Where cat vision really shines is at night; cats have six to eight times more rod cells, which can detect light at low levels, than humans do.
Credit: Nickolay Lamm
When Fluffy goes crazy for laser pointers, shiny objects and people's ankles, just what is she seeing?
Cats' fondness for pouncing on feet and feathery toys may be rooted in their hunting instinct, but it also has a lot to do with their unique vision. And, as it turns out, scientists know a lot about what cats see.
Now, a new set of images, by artist Nickolay Lamm, tries to capture the differences between cat vision and human vision. Whereas humans are able to see more vibrant colors during the day, their feline companions have the edge when it comes to peripheral vision and night vision. [Images: See What a Cat Sees]
Cats have a wider field of view — about 200 degrees, compared with humans' 180-degree view. Cats also have a greater range of peripheral vision, all the better to spot that mouse (or toy) wriggling in the corner.
Cats are crepuscular, meaning they are active at dawn and dusk. That may be why they need such good night vision. Their eyes have six to eight times more rod cells, which are more sensitive to low light, than humans do.
In addition, cats' elliptical eye shape and larger corneas and tapetum, a layer of tissue that may reflect light back to the retina, help gather more light as well. The tapetum may also shift the wavelengths of light that cats see, making prey or other objects silhouetted against a night sky more prominent, Kerry Ketring, a veterinarian with the All Animal Eye Clinic in Whitehall, Mich., wrote in an email. [10 Surprising Facts About Cats]
Their extra rod cells also allow cats to sense motion in the dark much better than their human companions can.
But felines don't have the edge in all areas. The human retina has about 10 times more cones, the light receptors that function best in bright light, than cats' eyes have.
"Humans have 10 to 12 times better motion detection in bright light than the cat or dog, since bright-light vision is a cone function," Ketring said.
Humans also have three types of cones, allowing them to see a broad spectrum of colors, with sensitivity peaks at red, green and blue. While cats may have three types of cones, the number and distribution of each type varies. In behavioral tests, cats don't seem to see the full range of colors that most humans do.
Some experts believe cats' "color vision is limited to blue and grays, while others believe it is similar to dogs', but with less richness of hues and saturation of the colors," Ketring said. Dogs see the world in fewer hues than humans do and cannot distinguish between red, yellow, green and orange objects. Fish, in contrast, can see ultraviolet wavelengths that humans can't see.
Humans also can see with much greater resolution, with a greater range of vibrant colors, thanks to their eyes' many cones.
Humans can see objects clearly at 100 to 200 feet (30 to 60 meters) away, but cats need to be no more than about 20 feet (6 m) away to see those same things sharply.
Because cats lack the muscles necessary to change the shape of their eye lenses, they can't see things clearly quite as close as humans can and need to be further away, Ketring said.
And though Fluffy may be better at picking up the darting and scurrying of a frightened mouse, there are many slow-moving objects that humans can detect with their eyesight that look stationary to cats.