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analogist_net's profile
James Wu
James Wu
James Wu
@analogist_net

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James Wu

@analogist_net

Engineer, neuroscientist. Building better neuroscience tools @WhiteMatterLLC. PhD from @UW @ctr4neurotech. He/him. Opinions my own. Every little thing matters.

Duwamish land
analogist.net
Joined May 2014

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    James Wu‏ @analogist_net 3 Jul 2018
    • Report Tweet

    James Wu Retweeted foone

    In honor of @Foone's thread on the *visual* quirks of our brains, let's talk about "how bullshit insane our brains are": sensory and motor systems edition.https://twitter.com/Foone/status/1014267515696922624 …

    James Wu added,

    foone @Foone
    You want to know something about how bullshit insane our brains are? OK, so there's a physical problem with our eyes: We move them in short fast bursts called "saccades", right? very quick, synchronized movements. The only problem is: they go all blurry and useless during this
    Show this thread
    11:35 PM - 3 Jul 2018
    • 672 Retweets
    • 1,222 Likes
    • Peggy J Pablo Salinas 〈Lacci|❄️|☢️🐇〉 Anathema the1truestripes Stephanie N Keyes Khady wØz DesertSageNatural
    10 replies 672 retweets 1,222 likes
      1. New conversation
      2. James Wu‏ @analogist_net 3 Jul 2018
        • Report Tweet

        Just like with the visual system, "hack your time perception" is trick is one that our brains employ a whole lot, to try make actions *appear* as if they're happening at the same time. This probably makes cause-and-effect easier to associate.

        1 reply 24 retweets 101 likes
        Show this thread
      3. James Wu‏ @analogist_net 3 Jul 2018
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        For example, try scratching your leg. You can feel your hand move; you can feel force in your fingers. You can feel your nail on your skin. Feels like they're all happening at about the same time, right? Wrong.

        2 replies 3 retweets 57 likes
        Show this thread
      4. James Wu‏ @analogist_net 3 Jul 2018
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        Your motor commands zips down from your brain through α-motor neurons to your fingers at around 100 m/s. They move; your legs then feel that scratch slowly at 40 m/s through type II sensory fibers. That signal's roundtrip takes 40-50 ms to just travel through your body.

        1 reply 3 retweets 75 likes
        Show this thread
      5. James Wu‏ @analogist_net 3 Jul 2018
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        After the sensory signals process, 100-200 ms has passed - from intent to conscious sensation. For reference, that would be the network roundtrip time from the US west coast, all the way to Europe, *and back*.

        2 replies 6 retweets 77 likes
        Show this thread
      6. James Wu‏ @analogist_net 3 Jul 2018
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        Crazy thing is, if that happened in a game you're playing, you would complain about lag. But for scratching, you *don't feel it at all* - your brain hacked time perception backwards to make you think the movement intent, the movement, and the sensation occurred at the same time.

        3 replies 11 retweets 115 likes
        Show this thread
      7. James Wu‏ @analogist_net 3 Jul 2018
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        This "hack sensations back in time" trick is also related to another effect - cancelling the sensations of your own actions. In movement neuroscience (and controls), this is the "efference copy". You expect the movement to feel a certain way, then you subtract that expectation.

        1 reply 4 retweets 71 likes
        Show this thread
      8. James Wu‏ @analogist_net 3 Jul 2018
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        Subtracting the expected sensation from the actual one -- that is, paying attention to what *wasn't* unexpected -- is a great strategy for a lot of reasons, chief among them being that the brain doesn't have to waste as much energy paying attention when things are *going right*.

        1 reply 3 retweets 70 likes
        Show this thread
      9. James Wu‏ @analogist_net 3 Jul 2018
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        Most people can't tickle themselves. Even using a tool, like a pen, it's very hard. Ever wondered why? One of the dominant reasons is that our movement efference copy is being canceled out, muting the feeling. But! That cancellation only works within about 150-200 milliseconds.

        1 reply 14 retweets 96 likes
        Show this thread
      10. James Wu‏ @analogist_net 3 Jul 2018
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        In a famous experiment in 1999, Dan Wolpert's lab built a robot. You moved the robot's arm, and another arm mirrored your movements, after an adjustable short delay. You could now in fact tickle yourself - as long as the robot copying your movements was delayed by about 200 ms.pic.twitter.com/u5d9gQc19n

        Tickling sensations using a robot that copied your movements is about the same as if someone else tickled you, after a 200ms delay.
        2 replies 33 retweets 165 likes
        Show this thread
      11. James Wu‏ @analogist_net 3 Jul 2018
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        This cause-and-effect hack works in other ways too. One of the ways it does so is in sensory integration. As we now know, if you see, hear, and feel what you think is same event, these signals are probably all hitting your brain at *very* different times.

        1 reply 3 retweets 66 likes
        Show this thread
      12. James Wu‏ @analogist_net 3 Jul 2018
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        So the brain tries its hardest to try to mix all of these senses together into what it thinks is the same event. One of the more famous illusions is the rubber hand illusion. Stare at a realistic rubber hand, and have someone touch IT - and your own hand - at the same time.

        1 reply 2 retweets 59 likes
        Show this thread
      13. James Wu‏ @analogist_net 3 Jul 2018
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        If your hand is hidden well enough, and the rubber hand is placed in a plausible position, and the two touches are at around the same time, many people start to feel like the rubber hand is part of their own body.https://www.youtube.com/watch?v=DphlhmtGRqI …

        1 reply 12 retweets 81 likes
        Show this thread
      14. James Wu‏ @analogist_net 3 Jul 2018
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        The word generally used is "ownership". It feels like it is part of you, because the sight of the touch, and the feel of the (separate) touch, are associated in your brain. If someone threatens the rubber hand with a knife, you flinch.https://www.the-scientist.com/infographics/infographic-the-rubber-hand-illusion-31592 …

        1 reply 4 retweets 66 likes
        Show this thread
      15. James Wu‏ @analogist_net 3 Jul 2018
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        It shouldn't be surprising to you know that this illusion starts fading if the two touches become separated by more than 200-300ms. http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0006185 …pic.twitter.com/tM945aFVGV

        Rubber hand illusion feedback delay: 200ms and the sensation disappears.
        1 reply 3 retweets 63 likes
        Show this thread
      16. James Wu‏ @analogist_net 4 Jul 2018
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        And if you're curious, our lab was looking into if this illusion works if you're stimulating the brain directly as well, by passing currents into the sensory cortex in patients with implanted electrodes. (Yes, it does.)http://www.pnas.org/content/114/1/166 …

        2 replies 2 retweets 62 likes
        Show this thread
      17. James Wu‏ @analogist_net 4 Jul 2018
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        Just as @Foone pointed that the visual system isn't like a camera streaming high-res video back at you, but is full of inconsistencies like blind spots and and selectively high-res (foveal) regions, the same thing is true of the skin on your body.

        2 replies 4 retweets 54 likes
        Show this thread
      18. James Wu‏ @analogist_net 4 Jul 2018
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        A classic example of "tactile acuity" is 2-point discrimination, whether you can tell that 2 pinpricks are, in fact, from 2 different pins. Well, you might know that this is about a millimeter of acuity in your fingertip, and many centimeters on your torso. That's not bullshit.pic.twitter.com/rvb3HEHaxc

        2-point discrimination: ranges from very fine on fingertip, to very course on torso and calf.
        2 replies 8 retweets 68 likes
        Show this thread
      19. James Wu‏ @analogist_net 4 Jul 2018
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        What is less well known is that this is affected by whether or not those pins touch simultaneously, or one after another. https://onlinelibrary.wiley.com/doi/full/10.1002/ana.24179 … It's also affected by whether or not the pins cause pain. It's even affected by whether you have chronic pain.

        2 replies 2 retweets 43 likes
        Show this thread
      20. James Wu‏ @analogist_net 4 Jul 2018
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        What is probably most bullshit is that tactile resolution is improved by whether or not you're *looking toward* the general direction of the touch. EVEN IF YOU CAN'T SEE ANYTHING BECAUSE YOUR ARM IS IN COMPLETE DARKNESS.https://www.sciencedirect.com/science/article/pii/S096098220100327X …

        2 replies 15 retweets 169 likes
        Show this thread
      21. James Wu‏ @analogist_net 4 Jul 2018
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        (A lot of this background -- and a lot of the ongoing work in neural touch perception at the @NeuralE_Ctr -- I learn from my colleagues @croninja1 and @djcald. Look for work from them.)

        1 reply 1 retweet 43 likes
        Show this thread
      22. James Wu‏ @analogist_net 4 Jul 2018
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        (Aside: while your 2-point acuity is ~1 mm, you can feel down to *nanometers* -- if you're allowed to stroke the texture. This is *awesome insane*, not *bullshit insane*. Basically, your brain turns the texture into a symphony of vibrating frequencies. http://www.pnas.org/content/110/42/17107.full …)

        1 reply 31 retweets 142 likes
        Show this thread
      23. James Wu‏ @analogist_net 4 Jul 2018
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        Another way your brain tries to blend vision and feel together is the size-weight and material-weight illusions. Basically, if a larger object weighs the same as a smaller object, the larger (less dense) object also *feels lighter*. As long as you get to look at it first.

        3 replies 8 retweets 71 likes
        Show this thread
      24. James Wu‏ @analogist_net 4 Jul 2018
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        Remember, the two objects weigh the same. And you can lift them the same way - by a handle on a string, say - and the bigger looking one still FEELS lighter.

        1 reply 3 retweets 50 likes
        Show this thread
      25. James Wu‏ @analogist_net 4 Jul 2018
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        Other bullshit insane effects include: - Lighter color feels lighter - More metallic feels lighter - Colder feels heavierhttps://link.springer.com/article/10.1007%2Fs00221-014-3926-9 …

        1 reply 8 retweets 104 likes
        Show this thread
      26. James Wu‏ @analogist_net 4 Jul 2018
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        A lot of this is from how the brain weighs (heh) prior experience. A lot of work has been done in trying to figure out how experience is used - but the short story is that through extensive training you can be tricked into thinking the reverse too, that smaller feels heavier.

        6 replies 3 retweets 79 likes
        Show this thread
      27. End of conversation

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