Whereas if the brainstem does not have such a 3D spatial attention system, then I’m not sure how else fear-of-heights could realistically work
I think part of the trigger is from the visual balance center. The eyes sense small changes in parallax as the head moves relative to nearby objects. If much of the visual field is at great distance (especially below, where the parallax signals are usually strongest and most reliable), then the visual balance center gets confused and starts disagreeing with the other balance senses.
If I’m looking up at the clouds, or at a distant mountain range, then everything is far away (the ground could be cut off from my field-of-view)—but it doesn’t trigger the sensations of fear-of-heights, right? Also, I think blind people can be scared of heights?
Another possible fear-of-heights story just occurred to me—I added to the post in a footnote, along with why I don’t believe it.
The vestibular system can detect whether you look up or down. It could be that the reflex triggers when you a) look down (vestibular system) and b) have a visual parallax that indicates depth (visual system).
Should be easy to test by closing one eye. Alternatively, it is the degree of accommodation of the lens. That should be testable by looking down with a lens that forces accommodation on short distances.
The negative should also be testable by asking congenitally blind people about their experience with this feeling of dizziness close to a rim.
I think I would feel characteristic innate-fear-of-heights sensations (fear + tingly sensation for me, YMMV) if I were standing on an opaque bridge over a chasm, especially if the wood is cracking and about to break. Or if I were near the edge of a roof with no railings, but couldn’t actually see down.
Neither of these claims is straightforward rock-solid proof that the thing you said is wrong, because there’s a possible elaboration of what you said that starts with “looking down” as ground truth and then generalizes that ground truth via pattern-matching / learning algorithm—but I still think that elaborated story doesn’t hang together when you work through it in detail, and that my “innate ‘center of spatial attention’ constantly darting around local 3D space” story is much better.
There are likely multiple detectors of risk of falling. Being on shaky ground is for sure one. In amusement parks, there are sometimes thingies that share and wobble and can also give these kind of feeling. Also, it could be a learned (prediction by the though assessor) reaction, as you mention too.
I think part of the trigger is from the visual balance center. The eyes sense small changes in parallax as the head moves relative to nearby objects. If much of the visual field is at great distance (especially below, where the parallax signals are usually strongest and most reliable), then the visual balance center gets confused and starts disagreeing with the other balance senses.
If I’m looking up at the clouds, or at a distant mountain range, then everything is far away (the ground could be cut off from my field-of-view)—but it doesn’t trigger the sensations of fear-of-heights, right? Also, I think blind people can be scared of heights?
Another possible fear-of-heights story just occurred to me—I added to the post in a footnote, along with why I don’t believe it.
The vestibular system can detect whether you look up or down. It could be that the reflex triggers when you a) look down (vestibular system) and b) have a visual parallax that indicates depth (visual system).
Should be easy to test by closing one eye. Alternatively, it is the degree of accommodation of the lens. That should be testable by looking down with a lens that forces accommodation on short distances.
The negative should also be testable by asking congenitally blind people about their experience with this feeling of dizziness close to a rim.
I think I would feel characteristic innate-fear-of-heights sensations (fear + tingly sensation for me, YMMV) if I were standing on an opaque bridge over a chasm, especially if the wood is cracking and about to break. Or if I were near the edge of a roof with no railings, but couldn’t actually see down.
Neither of these claims is straightforward rock-solid proof that the thing you said is wrong, because there’s a possible elaboration of what you said that starts with “looking down” as ground truth and then generalizes that ground truth via pattern-matching / learning algorithm—but I still think that elaborated story doesn’t hang together when you work through it in detail, and that my “innate ‘center of spatial attention’ constantly darting around local 3D space” story is much better.
There are likely multiple detectors of risk of falling. Being on shaky ground is for sure one. In amusement parks, there are sometimes thingies that share and wobble and can also give these kind of feeling. Also, it could be a learned (prediction by the though assessor) reaction, as you mention too.