Reality is what it used to be
February 13, 2016 4:59 PM   Subscribe

The Brain: What is Reality To conjure a reality from all [that] sensory information your brain needs about half a second.

Dr David Eagleman (previously) meets some interesting people while trying to work out how the brain constructs reality.

Paralympic skier Mike May made international headlines in 2000 when his sight was restored by a pioneering stem cell procedure after 40 years of blindness.
But a study published three years after the operation found that the then-49-year-old could see colors, motion and some simple two-dimensional shapes, but was incapable of more complex visual processing.
He can't ski with his eyes open.

Alyssa Brewer recreates the classic Erismann experiment with left-right prisms - In this study, we exploit the dynamic nature of posterior parietal cortex to examine cortical functional plasticity induced by a complete reversal of visual input in normal adult humans

Cold Blue Luke, sent to the Hole in Alcatraz - ' I remember going on these trips. One I used to remember was flying a kite. It got pretty real. But they were all in my head".

Different parts of our vision have various different functions. When we look at a painting, we’re typically using what is called “foveal vision.” This is the optical function we use to see fine details. At the very center of our gaze, our visual acuity is amazingly sharp. However, the center of the gaze focuses on a relatively small point and at the periphery, our visual acuity (known as “resolution” in neurological circles) drops dramatically... Russian psychologist named Alfred Yarbus invented an apparatus in the 1960s that would provide insight into the phenomenon of eye movement.

Ellen Saks - One day, and without reason, she suddenly left her classroom and started walking home. It turned into an agonizing journey in which she believed all the houses in her neighborhood were transmitting hostile and insulting messages directly into her brain. Five years later, while attending law school at Oxford, she experienced her first complete schizophrenic break. Saks struggled over the course of the next decade, but she came through thanks to medication, therapy, and the support of friends and family.
TED talk
Previously
posted by asok (12 comments total) 35 users marked this as a favorite
 
Erismann/Kohler-type experiments have always freaked me out because the effect persists for a time after the visual distortion is removed. I'd be worried it would be permanent... oops, you broke your brain! Sorry!
posted by Robin Kestrel at 8:01 PM on February 13, 2016


Mark Changizi explains visual illusions as resulting from the mind's attempt to "predict" the present in order to compensate for perceptual latency.

Anticipating the future to 'see' the present by Benedict Carey, The New York Times (June 10, 2008)
posted by 0rison at 8:24 PM on February 13, 2016


is there a (scientific) name for 'brain delay'? like what's the term for 'how long it takes -- thresholds of simultaneity, succession and integration -- for a stimulus to reach (or produce) consciousness'?
posted by kliuless at 9:41 PM on February 13, 2016 [1 favorite]


It is interesting when you notice errors in your perception created by your brain making assumptions of what it thinks it sees, Hey there's a orange tabby cat ,you think you saw a cat pretty clearly so you turn to get a better look, but it is just a red lava rock, but if you think quick you can pull up the indistinct image of the cat you did not see in your minds eye.
posted by boilermonster at 11:32 PM on February 13, 2016 [1 favorite]


kliuless: "is there a (scientific) name for 'brain delay'?"

The technical term is latency.

If you can imagine visual information, for example, flowing from the retina, through the thalamus (the lateral geniculate nucleus initially) into visual cortex, through parietal and temporal processing, then into higher order areas, zooming along to pre-motor and motor cortices, and eventually back out either to the muscles around your eyes (allowing you to saccade, ie to look at the thing you are perceiving) or into another motor actuator, then its easy to understand that latencies increase through the system. Early visual areas have very short latencies of 20-50ms, and fast human reaction times are 100-300ms so perceptual processing takes place somewhere between these times.

Whats really cool though is that the information doesnt only flow in one direction. Theres a TON of feedback information, so almost every feedforward route has a parallel feedback route too. What this means is that earlier areas can get information about what the system thinks is happening (what you are perceiving) a little later than it gets the sensory information. So if you are looking for your friend who you know is wearing a red shirt, area V1 (the first visual area) will send info down the line about all objects at about 50ms, and at about 800ms V1 can tell the difference between red things and things that arent red based on info it gets back from up top. We call this the effect of attention by the way.

IAAVN (I am a visual neuroscientist, studying attention and perception), so pardon the pedagogy ;)
posted by Illusory contour at 6:56 AM on February 14, 2016 [10 favorites]


Erismann/Kohler-type experiments have always freaked me out because the effect persists for a time after the visual distortion is removed. I'd be worried it would be permanent... oops, you broke your brain! Sorry!

I had a professor who did vision psychology and claimed that he had spent so many hours staring at McCullough stimuli that viewing the test pattern without seeing the induction pattern would still produce the effect, even after years/decades.

Also, to expand on the feedforward/feedback connections Illusory contour mentions, one attempt at developing a unifying framework for understanding the brain is Predictive Coding, which says that the feedforward connections carry information about the discrepancy between the input a particular neuron/brain region was expecting to receive and the input it actually received, while feedback connections carry information that tries to "explain away" the discrepancy. Predictive Coding has done a really good job at explaining some of the types of neurons observed in e.g., primary visual cortex, and the idea is that the framework could be expanded to include the entire neocortex, including areas in prefrontal cortex that are responsible for high-level cognition. Andy Clark has a pretty good recent review of predictive coding.

IAACN (computational neuroscientist; I have a model of predictive coding in PFC; I regret nothing)
posted by logicpunk at 8:10 AM on February 14, 2016 [5 favorites]


And yet somehow humans are capable of returning a tennis serve and hitting a baseball. It really makes the whole event much more amazing when you think about it.
posted by humanfont at 9:16 AM on February 14, 2016 [2 favorites]


Apparently returning a tennis serve is possible as the player returning gets all their information from the posture and movement of the server and the racquet. There simply is not time to watch where the ball is going and react to that, the decision is made before the ball leaves the racquet.

This is also how a googly works in cricket, the posture says one thing and the ball does another.
While a normal leg break spins from the leg to the off side, away from a right-handed batsman, a googly spins the other way, from off to leg, into a right-handed batsman (and is distinct from an off break delivery). The bowler achieves this change of spin by bending the wrist sharply from the normal leg break delivery position. When the ball rolls out of the hand (from the side near the little finger, as in a normal leg break), it emerges with clockwise spin (from the bowler's point of view). A googly may also be achieved by bowling the ball as a conventional leg break, but spinning the ball further with the fingers just before it is released.
posted by asok at 11:39 AM on February 14, 2016


The segment on how babies learn to integrate sight and touch is interesting and seems logical but... a foal is up and walking in an hour or so and nursing within three hours. So it seems that some brains contain an extraordinary amount of innate knowledge.

Our understanding of human development is encumbered by how immature humans are when born. It may be that a baby has to reach a certain amount of physical maturity before she is capable of certain innate behaviors. How much of walking, for instance, is learned and how much is simply waiting for physical development to mature to where it's even possible? It must be some combination of both, and it probably varies among species.

I'd wager, however, that we credit too much to learning and too little to physical maturation. Innate behaviors seem (to me) more mysterious than learned ones. Are we inclined to discount them for that reason?
posted by sjswitzer at 11:48 AM on February 14, 2016


cool post- I love stuff like this. thanks!
posted by GospelofWesleyWillis at 12:34 PM on February 14, 2016


If you have time to watch the second episode, sjwitzer, you can see his ideas about the advantages of humans not having innate behaviours.
posted by asok at 4:00 PM on February 14, 2016


you can see his ideas about the advantages of humans not having innate behaviours.

I think we don't so much have innate complex behaviors, generally, as certain classes of innate tendencies. We definitely have some very simple innate behaviors, like suckling, that may arise and fall by the wayside at different developmental stages. And in a certain very crude sense, eating is probably innate. But we seem to be very adaptable and variable, and so the majority of our complex behaviors are shaped mostly by social and environmental conditioning. That's just how it seems to me as someone with an amateur interest in thinking about these things.
posted by saulgoodman at 6:20 PM on February 14, 2016


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