This phenomenon - when you look away from a moving thing, and you briefly see illusory motion in the other direction - is the "Motion Aftereffect," and it comes from some very basic brain maneuvers. Who wants to join me on going full #NeuroThursday here? en.wikipedia.org/wiki/Motion_af…
Most neurons in the brain (and elsewhere) do this thing called "adaptation," where they accept whatever's going on as the new normal. For example, if you sit down with your laptop on your lap, you'll soon stop noticing the weight.
This can arise from the crudest single-cell level: some ion channels in the cell membrane have negative feedback loops that self-dampen.
Adaptation is super useful. There are a lot of variants and theories, but think of it as a mechanism to keep the meter from getting "pinned." If your mechanism (neuron) has a limited range, you can cover anything if you're willing to keep recalibrating around whatever arrives.
So if you stare at a moving object for a little while, your brain* recalibrates to that motion. It says "Leftward flow is the new normal, got it." Then you look at an unmoving object, and your brain says, "This is moving rightward compared to normal!"
(Oh hey, what's that asterisk? Is something neurosciency gonna get MORE COMPLICATED? You betcha!)
That little voice in the earlier tweet might be in your brain - there are plenty of secondary visual areas (especially ones called V3A and V5) that detect motion, and thus could be the ones adapting here.
But that voice might also be in your eyes. As I've discussed before, your eyeballs do a lot of fancy footwork. (Eyework?) I talked about it before in the context of slow/solstice vision.
Those eyeball network cells ("retinal ganglion cells") do a lot of visual preprocessing. Here's an image of them doing color contrast. Looks complicated! But the gist should be clear...
...these retinal ganglion cells combine information from a bunch of your light-sensitive cells. You can (hopefully) see how that might be enough to detect motion.
So to make a long story only as long as necessary: motion-sensitive retinal ganglion cells might be the ones producing the motion aftereffect.
And lo, a #NeuroThursday (NeuroTuesday?) lesson for you home #neuroscience fans: sometimes, the cause of a big conscious perceptual phenomenon is a little cellular recalibration property.
Thanks, world! If this helped you adapt to the scroll of your twitter feed, share this around, or check out my other work! benjaminckinney.com/publications/

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More from @BenCKinney

Jul 8, 2021
Welcome to this week's edition of, "I'm a neuroscientist, and this thread is spot on."

Physical limits, including strength, are a brain game.
A classic (apocryphal?) study: tell people to bike as fast as they can. Let them see their RPM meter.

Make 'em do it again - but tweak the RPM meter so it reads low. And they'll blow past their original "as fast as they can" to make the (apparent) RPM match.
An even better illustration of this effect is in stroke patients. One common side effect of stroke is hemiparesis - weakness on one side of the body.

But wait. Why does brain damage cause muscle weakness?
Read 10 tweets
Jul 1, 2021
As a neuroscientist who studies handedness: this is spot on.

Handedness is congenital, not learned. But the frequency of left-handedness varies between cultures - in a way that almost certainly reflects social acceptance, not heredity.
The most interesting data on this come from China. Most East Asian cultures have a lower prevalence of left-handedness than Europeans. But, again, this is not genetic. How do we know? Hong Kong.
Globally, left hand preference runs about 10%. Based on studies of art history, this value is pretty much stable across continents and millennia. I went into detail on the deep historical data in this ol' thread. benjaminckinney.com/handedness-acr…
Read 15 tweets
Dec 14, 2020
In case anyone had doubts that @/longshotpress was a bad actor, they doxxed me today.

I'm not afraid of them. My boss knows I do this. But do you think ANYONE should submit to a publisher who'll track down your real name & address, and publish it online, if you criticize them? Screenshot of Longshot Pres...
If you're new to this whole disaster, I've tracked Longshot's asshattery via this post here, ever since it started in February. Feel free to report 'em, of course. (And let me ping @victoriastrauss for this new round of misbehavior.) benjaminckinney.com/writer-warning…
Now that their original tweet is gone: in case it isn’t obvious, I added all those grey boxes myself. Mr. White posted my contact info in full.
Read 4 tweets
Oct 19, 2019
Alright, #sciencefiction #neuroscience fans: this is the content you’re here for! In ~30 minutes, I will livetweet this #sfn19 “Dialogues Between Neuroscience & Society” talk on the future of AI and machine learning in human society. Bio of speaker Fei-Fei Li for “dialogues between neruoscience & society” talk
Any minute now we should be underway with the #SfN19 Dialogues Between Neuroscience and Society talk by @drfeifei on how AI can - and should - change the human experience. Stay turned for livetweeting!
Yes, it is 11:10. No, the talk has not started. We haven’t even begun introductions yet. Stay patient, friends!
Read 75 tweets
Jun 20, 2019
Inhale deeply, and enjoy the aroma of #NeuroThursday, because this week I want to talk about smell, taste, and emotion – inspired by @tinaconnolly's Nebula- and Hugo-finalist novelette, "The Last Banquet of Temporal Confections." A perfume bottle, labeled
If you haven't read it, it's a wonderful story about memory, food, cruelty, and empathy. But you don't need to read it for this thread. I'm here to talk about neuroscience, not pastry-magic. tor.com/2018/07/11/the…
Tastes and smells are notoriously emotional. Smells can evoke a flood of memories, with all their associations. Freshly-cut grass, your partner's favorite flowers, the spices of your favorite meal, or the ammoniac strike of a campground toilet. Why so strong?
Read 28 tweets
Jun 15, 2019
Let me know if y’all want a neuroscience on this!
So a very quick #neuroscience on this: initial visual processing in the brain (and retina) works through contrasts. Your brain sharpens differences/edges because that’s where information is...
Your neurons are tuned to heighten/inhibit each other in a way that magnifies differences. So when a neutral color goes up next to red, your brain magnifies that difference and makes the neutral seem as not-red as possible.
Read 6 tweets

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