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Comment by BugsJustFindMe | Hacker News Reader

Only across time via parallax motion and depth refocusing, neither of which are available on the screen. And both of those signals are extremely secondary to binocular sight. There's a reason that people with strabismus lose depth perception. Their point stands.

(Though Apple could technically do a parallax effect by face tracking if they wanted)

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> There's a reason that people with strabismus lose depth perception.

Still we don't stumble onto things nor do we fail recognise what is on a glass vs inside. Even if we do not have binocular depth perception, we actually perceive depth irl just fine.

And people with binocular vision also fall for depth illusions just fine, too. The brain does a lot of predictive processing. It would be too inefficient to be constantly relying on such details for basic tasks.

> Even if we do not have binocular depth perception, we actually perceive depth irl just fine.

I don't think it's everyone of us because I struggle somewhat with pouring things into small openings (eg refilling a small bottle from a bigger one) and most ball games (tennis, table tennis) are difficult.

I don't think it makes depth perception a problem, but I think it's unarguable mine isn't as good as the people I know with binocular vision.

I don't know about your experience or situation, but a confound is that usually people with strabismus have bad eyesight in other aspects in general too. Usually, developing strabismus is the result of other issues with eyesight. The obvious confound is basically having only one good eye to use at a time, and thus also less neural pathways developed and utilised than those who use 2 eyes. This could make visual perception tasks like tracking a fast moving ball harder regardless of the actual role of depth perception in it. There could be tasks where reliance on perceptual cues for depth perception is less effective, but I wouldn't think a moving ball is that kind of task.

You might well be right. My eyes are definitely not great on top of the strabismus and lack of binocular vision.

One of the main issues with tracking things is focus switching from one eye to another based on where it's moving.

That said I do think the issues with pouring things is more of a depth perception issue. I basically have to switch focus from one eye to another to be satisfied I'm aligned where I want to be.

Pouring things sounds more like sth that could be a depth perception issue, true, though I never actually noticed that for myself. I believe I find it harder than usual passing a thread through a needle though because of depth perception issues.

It's good that you don't have trouble getting through life, but "just fine" is not a measurement. Lacking binocular convergence inarguably diminishes perception even if not 100% gone completely.

Measurements actually support that [0]. I am pretty sure you could devise some scenarios where individuals with strabismus do not perform as well, but for most irl scenarios there is no difference. Compensatory mechanisms do the job just fine, and even those with normal eyesight do not rely solely on binocular convergence either. Our brains don't usually rely on a single signal to make sense of the world, and predictive processing plays a huge role for constructing the image of the world around us, which is also why depth illusions work. Even for those with normal binocular convergence, its contribution for making sense of depth is prob smaller compared to other perceptual cues.

[0] Zlatkute et al 2020, Unimpaired perception of relative depth from perspective cues in strabismus. R. Soc. Open Sci. 7: 200955. https://doi.org/10.1098/rsos.200955

That article does not seem to support your point. They're not measuring depth perception, they're measuring whether people with strabismus have managed to learn perspective cues in 2D images, and, in fact, the article explicitly states agreement with the point you're arguing against.

> Strabismus disrupts sensory fusion, the cortical process of combining the images from the two eyes into a single binocular image [3–6]. The main perceptual consequences of lack of fused binocular images is diplopia (double vision) and a lack of binocular depth perception.

Just because those with strabismus can use monocular cues to inform them of relative depth does not mean that they have the same level of depth perception as those with normal binocular convergence.

The best example of this is sports, but as another example I'm legally disallowed from driving an articulated vehicle -- for what I personally think is a pretty good reason. Anecdotally, compared to friends and family my depth perception is dogshit.

You quote:

I am speaking specifically about whether people with strabismus have issues with depth perception or not. Obviously "strabismus disrupts sensory fusion" as you do not combine the input of the 2 eyes, and obviously this is a problem outside of depth perception. Moreover, most people with strabismus have bad eyesight more generally, as a common path to develop strabismus is having one eye much worse than the other. I am not saying strabismus is not an issue, I am saying that people with strabismus can still develop normal levels of depth perception in most irl situations by compensating with perceptual cues.

The article specifically tests whether people with strabismus had problems developing depth perception. If binocular depth perception was necessary for developing depth perception, they would have found that people with strabismus have impaired depth perception with 2d images. They didn't.

Again as I wrote to the other commenter before, I do not know about your situation, but I am curious about how you compare depth perception specifically with your friends and family. Having problems wrt visual perception does not mean that "lack of depth perception" is the issue. Using only one eye at the time is a huge issue by itself that makes vision harder, and a huge confound to control for in such comparisons.

they do parallax effect for some things, but not for all liquid glass widget (it would be interesting but probably too much)

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