Now that you've mentioned it, I wonder how much cats (or humans) rely on lens-focus for distance cues ... I'm pretty sure that most of it is done with parallax, and I know some is done with motion/size cues (Δsize/Δtime or comparison of expected-size-for-that-shape with image-size), but I was under the impression that little or none came from lens-focus. Hmm. Do we figure distance from stereo by feeling the position of each eye, or by comparing parallax errors between the eyes? If the proprioception in those muscles is accurate enough, then we could get information from the tension of the lens-focusing muscles, but I don't know whether we (or cats (or horses)) make any use of that information normally.
If we do rely on lens-focus for distance, then we should be worse at judging distances in bright light (when our pupils are small and greater DOF makes more things look in focus) than in low light (when "in focus" is a more precise indicator of exact focussing distance) ... unless the other methods we use are improved by more light more than lens-focus feedback is worsened by it.
Looks like I'll have to look for studies of distance perception in one-eyed humans, in addition to everything else. And walk around for a while with one eye closed myself.
Your description of horse behaviour sounds to me like they're using parallax to verify distance, just without being able to use both eyes at the same time to do so. (Much as astronomers measure distances to stars.) But I obviously have a lot of reading to do!
Actually the convergence and the focus reflexes are pretty tightly bound; that is what makes the "Magic Eye" pictures and other stereograms so difficult and eye-wrenching to view. One has to consciously disconnect the two accommodations that we have been training to couple all our lives.
There's some evidence that much of the depth perception comes from difference in geometry of the images in the two eyes, not the pure parallax in itself. We see the differences in distances of complex shapes, not the distances to simple point objects. Even though there is a mechanistic similarity to the split-image distance meter, apparently the human perception does not work quite that way.
From what I recall, distance perception for monoptic humans mostly comes from motion cues, often requiring a movement by part of the observer.
Looks like I'll have to look for studies of distance perception in one-eyed humans, in addition to everything else. And walk around for a while with one eye closed myself.
I don't have stereoscopic vision unless I'm wearing glasses. (One eye nearsighted, one eye farsighted). There's this weird mental lurch when I put my glasses on and everything jumps into 3-D...
While Maryland required me to wear my glasses to drive, neither Delaware nor Washington State tests the eyes separately, so it's been years since I've been forced to wear my glasses for any particular activity.
The brain adapts by considering a variety of circumstantial clues - relative sizes, atmospheric blurring, parallax, prior knowledge, eclipsing, etc. I don't know of any scientific studies of the matter, though. (Sounds like a job for medline...)
(no subject)
If we do rely on lens-focus for distance, then we should be worse at judging distances in bright light (when our pupils are small and greater DOF makes more things look in focus) than in low light (when "in focus" is a more precise indicator of exact focussing distance) ... unless the other methods we use are improved by more light more than lens-focus feedback is worsened by it.
Looks like I'll have to look for studies of distance perception in one-eyed humans, in addition to everything else. And walk around for a while with one eye closed myself.
Your description of horse behaviour sounds to me like they're using parallax to verify distance, just without being able to use both eyes at the same time to do so. (Much as astronomers measure distances to stars.) But I obviously have a lot of reading to do!
(no subject)
There's some evidence that much of the depth perception comes from difference in geometry of the images in the two eyes, not the pure parallax in itself. We see the differences in distances of complex shapes, not the distances to simple point objects. Even though there is a mechanistic similarity to the split-image distance meter, apparently the human perception does not work quite that way.
From what I recall, distance perception for monoptic humans mostly comes from motion cues, often requiring a movement by part of the observer.
(no subject)
I don't have stereoscopic vision unless I'm wearing glasses. (One eye nearsighted, one eye farsighted). There's this weird mental lurch when I put my glasses on and everything jumps into 3-D...
While Maryland required me to wear my glasses to drive, neither Delaware nor Washington State tests the eyes separately, so it's been years since I've been forced to wear my glasses for any particular activity.
The brain adapts by considering a variety of circumstantial clues - relative sizes, atmospheric blurring, parallax, prior knowledge, eclipsing, etc. I don't know of any scientific studies of the matter, though. (Sounds like a job for medline...)