What does the world look like to a cat?

Factual Questions
1

Not talking so much about perception as the optics; I’m wondering how much difference it makes to have pupils that aren’t circular like ours.

I suppose I should mock up a camera with a non-circular aperture, but we should be able to work this out:

The smaller the pupil/aperture, the greater the depth of field, but a cat’s pupil is shorter in the horizontal dimension only

it also means that the circle of confusion is not actually a circle.

but what does this mean in practical terms?

I’m thinking that it must mean (very roughly) that the horizontal resolution is sharper than the vertical.

Any thoughts?

2

Geez, that’s a good one. I’ve heard that a cat can more easily follow horizontal motion than vertical, but this may be a UL. If it’s true, it might be related to the optics, or it might be some kind of bias in the brain.

Fascinating…

3

I would suspect that all animals with two forward facing eyes set horizontally in the skull follow horizontal movements easier (partly because your field of view is a little wider than it is high?). It’s easier to test on cats because they are prepared to sit down and follow an object with their eyes for seemingly infinite periods of time while you take notes. And yes I have tested it on my cats and it seems to be true.

4

So, Sylvester would have a better chance of catching Speedy Gonzales than Tweety Bird!

5

A gigantic collection of servants.

6

Actually, I suspect the world looks like collection of Cat Toys. (Anything not nailed down is a Cat Toy).
As far as the slit pupil thing goes, the quotation above about horizontal vs. vricalmotion comes close, bt doesn’t quite get to the truth. Here is the real deal:

The resolving power of a optical system depends upon a number of factors, but all other things being equal, the larger the aperture is, the greater the resolving power (perversely, the larger the aperture, the smaller the f/# is. Don’t blame me for this – I didn’t come up with the definitions.).

However, when your system gets flooded with light, you have to close the aperture (“stop down” the system, to you photographers). You trade off being able to see against better resolution. The human eye, and most animal eyes, and camera lenses all solve thi problem with a aperture that remains cicular, but shrinks down in diameter. You lose resolution eqally in all directions.

The cat eye, however, along with snake eyes and a few others, keeps the same vertical dimension, and only shrinks horizontally, frming a vertical slit. As a result, the cat retains excellent vertical resolution (it can see really fine detail of horizontal objects), but has even worse horizontal resolution than your eyes.

Why is this? It may soundcorny, but it’s the only solution that makes sense to me – cats want to be able to see things like mouse tails, that are really small verticaly and lie out horizontally, but they don’t care about seeing grass, which is very fine horizontally. In fact, it works to the cat’s advantage to be able to see the mouse tail and NOT see the grass. Snkes, too, would like to be able to see mice and other prey amidst the grass.

I have to point out tha Big Cats, like lions and tigers, don’t have vertically-slitted “cat’s eyes”. (Look closely at photos of them sometime, or go to the zoo.) This, I think, means that they don’t particularly want to see fine vertical detail – ions don’t hunt mice, for the most art. Ths also means that those reconstructions of T. Rex and other big dinosaurs that show them with snake-like vertical pupils are almost certanly off the mark.

For the record, the frequency response of an optical system i called the Modulation Transfer Function, or MTF. I worked for a company that measured this for eight years, but we never discussed the issue of cat’s eyes. I ant to write a detailed article about t someday.

7

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8

To my wife’s and my cats, I am sure we for the most part look like animated cat food despensers and door openers.

9

That’s correct from a physics standpoint, but I’m not sure if the aperture is the limiting factor of resolution in human and feline eyes. I haven’t noticed my eyesight get worse on a bright summer day.

The non-circular aperture will probably affect out-of-focus views, though. When we see a point of light out of focus, they are circular. When you see a photo with an out of focus light, the light sometimes look hexagonal or pentagonal, because that’s the shape of the camera’s iris. A cat will presumably see out-of-focus lights as vertical lines.

10

Many plains predators, such as lions, have a very high resolution zone in a band across their eye and much poorer vision up and down which gives a letterbox sort of view.

Since the only thing of interest to them is in a wide panoramic view their eyes have developed to be superior in this area.

11

When I torment Rastakitty with the laser pointer, he’ll follow it intensely when I move it across the floor. However, when I move it up and down the walls, he quickly either gets confused or loses interest.

More evidence for the horizontal vs. vertical theory.

12

In Laser Safety classes they always tell you not to work in a dark or dimmed lab when working with high power lasers. Why? Because in dim light your iris opens up wider and the resulting focal spot on your retina is smaller, so the power density is greater and the risk of injury is increased.

The iris certainly is the limiting aperture in both human and cat eyes. I’ve dissected human and cow eyes, and looked at anatomy books – there’s nothing else in the way. The density of rods and cones doesn’t seem to be the limitation.

I agree that I haven’t noticed a perceptible change in resolution in going from dim to bright circumstances, but I haven’t really looked. I should try to see if anyone else has ever studied this. But judging from my first paragraph, it is certainly believed to be the case in the laser community.

13

Or could it be because RK knows he can physically follow the light spot on the floor more easily than the wall?

14

I had a friend who used to torment his cat this way. I have to admit that the cat followed the spot both horizontally and vertically, and the cat tried to follow the spot WAYYY up the wall. If you’re a true cat, you don’t stop to think if you can do it or not.

15

IANA optician, but luckily my husband is, and you do have slightly better resolution with a dilated eye. Resolution is equal to the wavelength divided by the diameter of the lens, so when your eye constricts from 7 mm (dark-adapted) down to 2 mm in bright daylight, you lose a factor of three in resolution! That’s one of the reason they usually give eye exams in a darkened room with an illuminated chart–you want viewing conditions to be optimal in order to determine the best correction to the lens.

I first notice that my prescription is getting a bit old while driving at night, and when I complained of this the optometist explained that this is typical. While driving because I’m looking into the distance a lot, and at night the resolution of my eye is better so I really notice that my glasses aren’t correcting as well, whereas during the day the lower resolution of the eye is a bigger effect than the fact that the image on my retina is slightly out-of-focus. (I should specify that I’m myopic, natch.)

You may not typically notice because seeing in low light has its own problems, such as rods being farther apart on the retina than cones.

16

I’ve noticed my cat’s eyes dilate when I’m playing with them…usually just before they attack me. If my cat is just sitting there and I engage her with something worth chasing she’ll hunker down and I’ve seen her eyes dilate to almost full aperature (her green eyes seem to turn black…it’s kinda cool). I assume this is to improve her resolution and/or tracking ability on her target since the light in the room hadn’t changed at all.

Also, as a point of trivia, I think cats have the physically largest eyes in relation to their head of any mammal.

17

Hehe…that sounds like I’m playing with eyes and not cats. Sorry for the bad grammar…I have two cats hence my confusion leading to the poorly written sentence. FTR I am talking about playing with my cats (either or both of them) who both have their eyes firmly attached to their heads.

18

HA! I was gonna say: that surely explains why they’d attack you! :smiley:

19

I know the iris defines the aperture, and a larger aperture is capable of higher resolutions. But that assumes that the retina and the optical quality of the lens are good enough to tell the difference. But if the resolution is limited by the retina and/or the optical aberrations, larger apertures do not help.

The theoretical resolving power of a 7mm aperture is about 15 arcseconds, and with a 2mm aperture it’s about 50 arcseconds, or 0.8 arcminute. (1 degree = 60 arcminutes, 1 arcminute = 60 arcseconds.) 20/20 vision is approximately 1 arcminute resolution, so you don’t need a dilated pupil to achieve 20/20 vision.

Actually, in real life, larger apertures can actually reduce the resolution. This is because larger apertures are more prone to optical imperfections and aberrations. Photographers know that many lenses perform better at F/8 than when wide open - that’s because the lens doesn’t have the optical quality to deliver a diffraction-limited image when wide open.