Here's another factor to throw into the mix: The eye adapts to different lighting conditions by changing the "film speed" in addition to the pupil size, so there's no one idea pupil size for any given lighting.
Whoops! Yeah, that throws a monkey wrench into my math! I did wonder about that -- it was part of what I was thinking when I wondered whether cats' eyes react differently to "overbrightness" than ours do, but it sounds like human eyes compensate as well ... Do you know whether the compensation is done in the eye, the brain, or both? 'Cause suddenly I'm not sure I understand how rods and cones work as well as I thought I did.
But this does explain how humans' pupils can get so much larger in response to sexual arousal even if there's plenty of light.
My understanding of rods and cones is that they optimize at different light levels. I get confused as to which are the rods and which are the cones, but my impression is that whichever ones are used for motion (and not used for color) (rods? maybe?) work better in lower-light situations. That is why under dim lighting -- half-moon light, e.g. -- we don't see color.
So it is conceivable (she said hypothesizing wildly) that when you do something which has to do with motion, the cat adjusts the aperture of her eyes to better track that, and that while your finger is still, she adjusts to optimize for color (perhaps to see if there is something tasty on your finger?)
All that said, there is something particular to cats eyes which are different from human eyes, which has to do with cats and light sensitivity. The inside of the eyeballs of we diurnal mammals (I know, I know, they weren't counting musicians) are black, as you might expect the inside of a camera to be. Light passes through the retina, which is smeared against the back of the inside of the eyeball (held in place by the optic nerve and the pressure of the vitreous humor) and then gets absorbed by the black surface (called choroid).
Cats have black choroid, too, just not underneath the retina. Instead, they have a tapetum (in/instead of?) their choroid. Tapetum is a beautiful pearlescent material. It is believed that the purpose of the tapetum is to reflect the light which has passed through the retina back through the retina to reactivate the rods -- making light twice as effective. That, btw, is what makes cats' eyes "glow" in the dark: the light bouncing off the tapetum and coming out through the iris. I understand the reason it is red is all the many blood vessels in the retina.
(BTW, I know about choroid and tapetum because when I was in HS, I had a job which entailed, among other things, doing eye dissections for the public at a science museum. We used cow's eyes. Cows are or were, evidently nocturnal; they have tapetums (tapeti?). "That's why, when you put a cow under your bed, its eyes glow.")
I have a dim recollection that cats have alot more, er, rods? (motion detectors) than, er, cones? (color detectors).
Our color-detectors tend to be in a might tighter clump than our motion-detectors, and I gather this is generally true for organisms with color vision. This explanation I heard was that this was to give us motion-detecting peripheral vision. For detecting whether something is leaping out of a tree at you, you don't need to visually parse its details, you just need to know it's approximate trajectory and velocity so you can get out of the way. It doesn't need to be in focus. Color however, is more useful if in an in-focus image, so it only makes sense for color-detectors to be in the area under the focal point of the eye.
(no subject)
(no subject)
But this does explain how humans' pupils can get so much larger in response to sexual arousal even if there's plenty of light.
Rods and Cones and Cats
So it is conceivable (she said hypothesizing wildly) that when you do something which has to do with motion, the cat adjusts the aperture of her eyes to better track that, and that while your finger is still, she adjusts to optimize for color (perhaps to see if there is something tasty on your finger?)
All that said, there is something particular to cats eyes which are different from human eyes, which has to do with cats and light sensitivity. The inside of the eyeballs of we diurnal mammals (I know, I know, they weren't counting musicians) are black, as you might expect the inside of a camera to be. Light passes through the retina, which is smeared against the back of the inside of the eyeball (held in place by the optic nerve and the pressure of the vitreous humor) and then gets absorbed by the black surface (called choroid).
Cats have black choroid, too, just not underneath the retina. Instead, they have a tapetum (in/instead of?) their choroid. Tapetum is a beautiful pearlescent material. It is believed that the purpose of the tapetum is to reflect the light which has passed through the retina back through the retina to reactivate the rods -- making light twice as effective. That, btw, is what makes cats' eyes "glow" in the dark: the light bouncing off the tapetum and coming out through the iris. I understand the reason it is red is all the many blood vessels in the retina.
(BTW, I know about choroid and tapetum because when I was in HS, I had a job which entailed, among other things, doing eye dissections for the public at a science museum. We used cow's eyes. Cows are or were, evidently nocturnal; they have tapetums (tapeti?). "That's why, when you put a cow under your bed, its eyes glow.")
Re: Rods and Cones and Cats
I have a dim recollection that cats have alot more, er, rods? (motion detectors) than, er, cones? (color detectors).
Our color-detectors tend to be in a might tighter clump than our motion-detectors, and I gather this is generally true for organisms with color vision. This explanation I heard was that this was to give us motion-detecting peripheral vision. For detecting whether something is leaping out of a tree at you, you don't need to visually parse its details, you just need to know it's approximate trajectory and velocity so you can get out of the way. It doesn't need to be in focus. Color however, is more useful if in an in-focus image, so it only makes sense for color-detectors to be in the area under the focal point of the eye.