The Speed of Short People

Robert Krulwich has a fascinating piece on NPR about the binding problem and the speed of nerve transmission. In essence, it takes a split-second longer for sensory signals to reach the brains of tall people, which means that their "now" is actually a little less timely. (This explains a lot about the NBA...)

Because for the taller person it takes a tenth of a second longer for the toe-touch to travel up the foot, the ankle, the calf, the thigh, the backbone to the brain, the brain waits that extra beat to announce a "NOW!" That tall person will live his sensory life on a teeny delay (at least as regards toe-touching). This, of course, could apply to all kinds of lower-extremity experiences -- cold or heat against the skin, tickles, rubs, hitting a soccer ball -- the list goes on and on.

The larger issue here is the "binding problem". At any given moment, billions of neurons all over the brain are lighting up, reflecting the hodgepodge of sensations simultaneously activating our sensory cells. Perhaps we have an itch on our thigh, and we're smelling a fresh pot of coffee, and we're looking at the pixels on a computer screen. We're also listening to the whoosh of the air-conditioner (and the distant hum of highway traffic) and just noticed that we're getting hungry.

The problem, of course, is how all those discrete perceptions (represented by distinct patterns of cellular activity) get bound together into a single moment of experience. The neuroscientist David Eagleman, however, proposes that the brain solves the problem by patiently waiting:

It may be that if the brain wants to get events correct timewise, it may have only one choice: wait for the slowest information to arrive. To accomplish this, [the brain] must wait about a tenth of a second. In the early days of television broadcasting, engineers worried about the problem of keeping audio and video signals synchronized. Then they accidentally discovered that they had around a hundred milliseconds of slop, and as long as the signals arrived within this window, viewers' brains would automatically resynchronize the signals.

What does this have to do with tall people? Because it takes a few extra milliseconds for the far-away body signals of a tall person to reach their head, his or her brain must wait a little bit longer. The end result is that the moment of binding - that fleeting neural representation of now - is late.

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Why would the brain want to "get events correct timewise"?
Does it really care that the simultaneous stubbing of our toes is experienced at the same time as seeing a car drive by?

Watching TV the brain needs to correct so the images and sounds reflect the simultaneity of ONE event (a newscasters speaking for example).
How on earth would the brain know that one discrete visual event (seeing cars) is simultaneous with a different physical one (stubbing toes)?

There is no "binding problem" for separate but simultaneous events.
Unless of course all tall people give themselves some serious training - I guess if they went round stubbing their toes and watching it happen their brains would slow down the image processing.
For every other toe stimulus the brain would have no idea how to delay/speed the image processing since you wouldn't be looking at your toe.
Frankly, Eagleman is full of it.
We clearly live our lives with a "now" that is a poor reflection of actual simultaneous events.
We just experience the signal arriving at the brain as-and-when.
The TV counterexample is clearly the exception rather than the rule since the brain knows it is experiencing ONE event not two.

If I'm understanding your article correctly, the brain tries to keep all disparate stimuli with different arrival times 'in sync' by some type of buffering of the signals. So, just how precisely do these signals line up to produce the sensation of 'now'? What is the duration of this 'now' experience? And does this duration vary for tall versus short people? In other words, is a tall persons 'now' a bit later than a short persons 'now' or is a tall persons now just a narrower window on the 'now' event?

Often in cases of a fast moving crisis (like an automobile accident), people experience a time dilation effect - events seem to move in slow motion as we consider all of our options and there is this sense of not really being there as the events unfold - could this phenomenon be related to this timing issue and the binding problem? It seems to me that if the brain stops trying to keep all the signals in sync but switches to a 'process as it comes in' mode, it would be able to react faster but would sacrifice the illusion a coherent experience.

This reminds me of our observations in the VR lab at Boeing, where subjects had to wait for the rendering of the scene to the viewing helmet catch up with their head motion. If we got slower than 100 msec delay, we entered the "barfogenic region" and subjects got quite dizzy from the timing disconnect.

By David Kerlick (not verified) on 19 May 2009 #permalink

That would explain that weird feeling I get when I go to Holland and it seems like all images lag a little and are composed of digital information and their shapes becomes a little shaky around the edges, almost pixalated and unreal. I guess I'm catching the delay.

Perhaps this helps explain why shorter athletes, who may not be as close to the hoop or as bruising on the line, are nevertheless often known for their quickness and their ability to "be everywhere at once."

This doesn't take into consideration the elasticity of time and space.

Consider the following example:
Total transfer time = ( DT + AL/AR ) x n
Where,
DT=Dentrite transfer
AL=Axon length
ATR=Axon transfer rate
n=number of neurons from toe to brain

Tall (2.2m)
Short (1.5m)
Both have 20 neurons from toe to brain
Both have DT=5ms
AL (tall) = 0.22m
AL (short) = 0.15m
ATR = 100m/s

Googled DT, ATR from here: http://people.eku.edu/ritchisong/301notes2.htm

Time Short = (5ms + 0.15/100)*20 = 130ms
Time Tall = (5ms + 0.22/100)*20 = 144ms

About 14ms difference -- this could be an issue.

But also consider that there is more significant sensory information coming from eyes, ears, tastebuds, etc - within a few, lets say 5 neurons and 0.1m away (30ms). The short person's "Now" perception window is 100ms (130ms-30ms) and tall person's is 114ms (144ms-30ms).

Did I do that right? (I mean as a first pass approximation)

The basic argument seems a bit weak here. As has been known with baseball players, if motion processing/planning starts the second the ball leaves the pitcher's hand, it would be impossible to hit a professionally thrown baseball. The body has all sorts of compensatory mechanisms that predict future motion or make future motion plans that fit into the system.

Perhaps a taller person takes slightly longer to adjust plans, but a larger person also has more mass and more momentum to change which would also cause a delay withou factoring in neural transmission times.

I think you should look into internal modeling, an umbrella term for forward and inverse models.

In particular, I think there's a paper called 'Why you can't tickle yourself' that talks about the general idea.

Although it's true that some sensations would take longer to get to a taller person's brain, I think most of the time that will only matter when something happens that the person's brain didn't (un/preconsciously) anticipate.

Frontal Cortex has alerted me to an interesting NPR radio segment on the fact that taller people have longer nerves and so will have slight sensory lag in comparison to shorter people. It prompted me to look up some of the research in the area and I found an eye-opening study looking at a range of factors that can effect nerve conduction. The researchers found that, after controlling for sex, age and temperature (it turns out your nerves are quicker when you're warm), there was a 0.27 m/s decrease in the conduction speed of one

Since the neocortex operates bidirectionally, with bottom-up processing carrying information about inputs and top-down processing continuously predicting and guiding the interpretation of those inputs, I'd be rather surprised if temporal binding didn't take advantage of the prediction that's going on anyway.

I think pretty likely that the brain's predictions of what's about to happen are used to allow earlier binding of events than waiting for the last input to arrive would, gently fudging sensory input to match expectations. Then, if the late-comer sensory input diverges wildly from expectations (such as in stubbing one's toe), the new input revises the already bound and experienced event.

Which would cast a different light on why, in stubbing one's toe, there is often a palpable moment of surprise before the pain and anger registers.

I think actually what happens is the brain uses predictive modeling to help keep track of stimuli (for example, you see someone reaching a hand out to touch your toe) and that makes up for the occasional delay of tactile sensation. It's only when a sensation (or possibly cognition) is unexpected that the brain has to figure out "What the hell was that?" that there comes a specific delay in processing. That would be what happens when someone sneaks up behind you and pokes you in the ribs, you jump and freak out because your conceived reality (to the best of your knowledge there's no one behind you) becomes different from your perceived reality.

In that case your brain has to unpack everything that inside it to figure out what was going on, creating the sensation of surprise. It's probably similar when someone gives you a piece of surprising news, your mind needs to reevaluate everything to account for the new data.

By George Jenkins (not verified) on 23 May 2009 #permalink

I agree with Nick, Eagleman is full of it. There's a real distinction between "differences in processing speed between individuals" and "Our brains are all synchronized to a universal clock and standard time-frames, and if one body has a longer transmission time toe-to-brain, that body's brain will go 'on hold' while waiting for the 'tardy' information to arrive... or maybe go out for a cup of coffee."

By Bob Ruhloff (not verified) on 23 May 2009 #permalink

This probably explains why TODDLERS can be everywhere at any time.

Clearly tall people will experience more propagation delay from toe stubs, but I suspect that is just a small piece of the puzzle, since signals must be processed once they reach the brain. Tall people also have (on average) slightly larger craniums, allowing for (possibly) more parallel processing of said signals. I.e., increased processing power may make up for reduced I/O speed.

On the other hand, tall people must process more inputs since the higher vantage point of their eyes, ears, etc. Thus they have a more distant horizon so their possibly more powerful brains must process more visual (and to a lesser extent, auditory) stimuli. Think this doesn't make much difference? On a flat sphere, the horizon from a five foot height is about 3 miles, whereas from a six foot height it is about 3.3 miles. Since the visible area is proportional to the square of the distance, that actually means that a six footer can see about 20% more area than a five footer.

That's a lot of extra work, but then it does allow tall people to see saber-toothed tigers first. :-)

(Jonah, I just started How We Decide this morning and have already decided (both rationally and emotionally) that I love it!)

actually this is about what it means to be conscious. it means remembering the totality of the state of the brain just a little while ago when the sensory input actually activated the neurons. ie, we see what feels like the present but we are actually remembering the very near distant past. all day long.

By gary weiner (not verified) on 27 May 2009 #permalink

One answer to Nick and other skeptics is that hierarchical synchronization of clusters of neurons probably permits the most information to be communicated per neuron.

This explains everything about my husband.

By amybuilds (not verified) on 10 Jun 2009 #permalink

I think this is correct in the sense that all humans are like a piece of wire. Shorter ones have more current but less resistance than longer or "taller" wires so they can get more voltage and it travels a shorter distance for shorter people. So taller ones will feel that delay because it is harder for it to go to their brains.

The basic argument seems a bit weak here. As has been known with baseball players, if motion processing/planning starts the second the ball leaves the pitcher's hand, it would be impossible to hit a professionally thrown baseball. The body has all sorts of compensatory mechanisms that predict future motion or make future motion plans that fit into the system.

Perhaps a taller person takes slightly longer to adjust plans, but a larger person also has more mass and more momentum to change which would also cause a delay withou factoring in neural transmission times.

I think you should look into internal modeling, an umbrella term for forward and inverse models.

In particular, I think there's a paper called 'Why you can't tickle yourself' that talks about the general idea.

Although it's true that some sensations would take longer to get to a taller person's brain, I think most of the time that will only matter when something happens that the person's brain didn't (un/preconsciously) anticipate.