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With the fear of sounding rude, this is incredibly cool. In the hope we have some neuro experts here on HN: 1. When the article says they can switch to self co

• Retric 9y ago
  3) They can control a subset of the other persons limbs. Seeing out of 3 eyes seems like a much stranger sensory system. It's not going to simply extend to a wider field of view because someone else is controlling the focus.
  • 35bge57dtjku 9y ago
    Isn't focusing done automatically anyway?
    • loa_in_ 9y ago
      I can do it consciously but also don't have to, so... hybrid?
  • chacham15 9y ago
    Is there even just a singular focus? Normally, both of a persons eyes are facing a singular direction which makes a large area of shared vision between the eyes (which allows a focus point anywhere in that field of vision). But with eyes which are pointed in a different direction this seems less likely. Does anyone have more info?
    • Swizec 9y ago
      I often wonder how birda do this (because I have one at home). Their eyes are on the side of their head, pointing in almost completely opposite directions. Yet they’re able to accurately land on things and generally exhibit behavior that indicates they have pretty good 3D vision. Then again my bird often sticks his foot out to step on my finger when the finger is still an inch away. So maybe not as good at depth perception as humans.
    • return0 9y ago
      strabismic people develop active mechanisms to inhibit the opposite eye to avoid / reduce double vision. in the end no matter how many eyes, what matters to the brain is to see something useful, so it will try to learn to suppress confusing information.
    • JohnBooty 9y ago
      I have one normal eye and one eye that has no lens, so I only see vague shapes and colors in that eye. There's no shared focus, per se. (The bad eye literally can't focus at all) I don't typically "pay attention" to the bad eye. Usually, they are "separate" and I ignore the bad eye. Sometimes I have really funny lapses in depth perception. Driving at night when the road is wet (and there are lots of weird reflections) is particularly tough. I can't see 3D movies... mostly. Sometimes that magical 3D effect kicks in for a second or two. When it happens, it's pretty cool. Then it goes away. haha. But, my brain does seem to assemble information from both eyes somehow. I can actually play most sports pretty well. I'm pretty decent at softball and tennis. I also avoided a serious car accident once thanks to that shitty eye. Was nearly broadsided right in the driver's door by somebody on my "blind" side, but that eye alerted me to an oncoming car (jackass running a red light) approaching at fairly high speed. She sheared my front bumper clean off (instead of plowing into my door, possibly killing me because it was a tiny little sports car with little side impact protection) because I hit the brakes at the last fraction of a second. I would wager that the conjoined twins' experience may be something like this. (Obviously, with more eyes involved)
      • a_rahmanshah 9y ago
        Interesting points, John. Would like to read more about your experiences. Are you anywhere on the interwebs?
        • JohnBooty 9y ago
          I'm flattered! I don't have much of a web presence these days but feel free to use my contact info in my profile or reply here if you have any questions. As far as I know my experiences are fairly typical for people in my situation though; I'm not sure I have anything unique to say. =)
  • JohnBooty 9y ago
    I'm nearly blind in my left eye (was born with a cataract; lens was removed at an early age before lens transplants were a thing) and I think I perhaps experience something similar. My vision isn't really integrated between the two eyes. It's hard to explain. I "think" with my right (good) eye. But then I also sort of have this auxiliary eye, my left eye. I can just see vague shapes and colors through it. It's just like this... separate camera or something. I can basically pay attention to one eye or the other; they're not really "together." Now obviously, unlike these twins, I don't have another person controlling it. But, I wonder if their experience is similar to mine. Like they have their "primary" eyes and then also this separate disconnected set of eyes they can pay attention to if needed/wanted.
    • PhasmaFelis 9y ago
      I have normal vision (with glasses) in both eyes, but I also have strabismus, that is, one eye turns inward a bit; so rather than seeing double, I use one eye at a time, and can switch from one to the other voluntarily. I just get peripheral vision from the "off" eye. I don't miss the depth perception much, but it does mean I get nothing from 3D glasses. With the modern polarized kind I can at least wear them and watch the movie normally; with the old red/blue kind, the whole movie would be red or blue depending on which eye I was using.
      • deleted 9y ago
        [deleted]
      • Brockenstein 9y ago
        I've experienced something similar. I kind of think that the other eye is still working and providing some depth perception, it's either that or after lifetime of single eye dominance/usage you just adapt and become very good at estimating and judging depth and distance. In my case never having normal vision, I don't really know what I am missing, if anything.
        • PhasmaFelis 9y ago
          Yeah! I did some reading and apparently binocular depth perception is the least important kind, and only works out to about six feet anyway; past that there's not enough parallax between your eyes to get any useful info. Judging distance by an object's surroundings is the most common way of doing it even for people with normal vision.
• SomeStupidPoint 9y ago
  As for 3, I too am curious: the article made it seem like they normally do a 3-1, 1-3 split on limbs but can each do 2-2 if they want. From a control theory standpoint, that make sense -- you have one person focused on arms and one focused on legs, instead of an even split. (Probably not so different from being right or left handed.) Is this accurate? Also interesting: the one that controls more arms is the outgoing and high-strung one, while the one that controls more legs is the quieter and relaxed one. It seems unlikely that these facts are uncorrelated, though the causal relationship is anything but clear. Incredibly, in an article full of pictures, they never actually tell you which twin is which and only address them as a unit of 'twins' in descriptions, which seems incredibly rude and depersonalizing to Krista and Tatiana. (Or, alternatively, never mention that the twins prefer to be spoken of as a unit -- which is itself an incredibly interesting fact.)
  • Chris2048 9y ago
    > It seems unlikely that these facts are uncorrelated Why does it?
    • SomeStupidPoint 9y ago
      Well, in a sample size of 1, it doesn't make a huge amount of sense to discuss correlation -- the two facts both happened, and so have 100% correlation on that sample size. (But this is a basically useless statistic for making any inferences.) The question was if we expect, given that it happened together here, we'd see it happen together more than random distribution would predict -- that is, that we see personality differences align with a split in limb control. Since they're both changes in the manner in which one interacts with the world, and my experience of the world changes in subtle ways when I, eg, use my left hand for certain tasks or sit in certain postures, I just find it unlikely that the alignment of limb control and personality are unrelated.
• return0 9y ago
  There is not a lot of literature about them, but from what i found their thalami are connected or fused together. Since thalamus is the crossroads for many sensory inputs the senses of one girl can pass on to further brain processing regions of both brains , e.g. their eye signals diverge and reach both girls' visual cortices. 1. Each brain controls more limbs than usual, but brains are plastic and can learn do that. It seems they have separate "personalities" however and they recognize themselves as different persons. So they don't "control" each other's consciousness although they seem to be able to communicate thoughts (not clear how) can control the limbs of the other, and can see what the other sees (e.g. with closed eyes, they can see what the other girl sees). Whats fascinating is how one of them can manage to override the movement signals coming from the other. Surely further examinations during their life will show how action initiation/inhibition happens in their brain. 3) It seems no, they dont control a limb simultaneously. They seem to be able to cancel the signals from the other person, presumably because their personal signals are much stronger (possibly because they have learned over time to do that ) or they have developed some mechanism to inhibit sensory signals from the opposite brain. This may be happening already at the level of thalamus where they are connected. Since their arms can possibly be controlled by both brains through the thalamic connection, i wonder if they can train themselves to use primarily the opposite person's limb, e.g. hand. It might be possible since the wiring is already there - it seems to only require sensorymotor traning. 2) I suppose you mean they have some kind of learning problems. But not really, people can learn and have normal IQ with much much less brain than what they may be allocating to the opposite body. And it's not even clear that they do that. They essentially share a thalamus but not much else , and even so, they dont seem to have less total thalamic mass than they would have separated . Also , thalamus being a relay rather than a decision taking region, it doesnt seem it would affect their intelligence too much. - http://ojs.library.ubc.ca/index.php/ubcujp/article/view/2521/182422 http://ojs.library.ubc.ca/index.php/ubcujp/article/view/2521...