January 18, 2007
Human Brains Limited Parallel Processing Capabilities

Vanderbilt University neuroscientists Paul E. Dux and René Marois used functional magnetic resonance imaging of human brains to discover how the brain responds to the need to perform two tasks at once. They discovered parts of the brain that are bottlenecks which serialize the processing of information for multiple tasks.

To overcome this limitation, Dux and Marois rapidly sampled brain activity using fMRI while subjects were performing two demanding tasks. Evaluation of the data produced by this rapid sampling method allowed them to characterize the temporal pattern of activity in specific brain areas.

The two tasks consisted of pressing the appropriate computer key in response to hearing one of eight possible sounds and uttering an appropriate syllable in response to seeing one of eight possible images. Different senses and motor responses were enlisted in order to ensure that any interference between the two tasks was not specific to a particular sensory or motor modality, but instead originated at a central information-processing bottleneck.

The results revealed that the central bottleneck was caused by the inability of the lateral frontal and prefrontal cortex, and also the superior frontal cortex, to process the two tasks at once. Both areas have been shown in previous experiments to play a critical role in cognitive control.

"We determined these brain regions responded to tasks irrespective of the senses involved, they were engaged in selecting the appropriate response, and, most importantly, they showed 'queing' of neural activity--the neural response to the second task was postponed until the response to the first was completed," Dux said.

"Neural activity seemed to be delayed for the second task when the two tasks were presented nearly simultaneously – within 300 milliseconds of each other," Marois said. "If individuals have a second or more between tasks, we did not see this delay.

What I'd like to know: Do higher IQ people have an enhanced ability to process two tasks at once? Or do they serialize just as strictly but finish processing each task more quickly?

When you do two tasks at once your response to stimuli for each task gets slowed for as much as a second. So all those people driving around with cell phones are at greater risk for causing an accident.

"I'm Australian, and it's illegal there, so I'm trained not to," Dux said. "Even so, I would never do it. Dual-task costs can be up to a second, and that's a long time when you're traveling at 60 miles per hour."

It would be really handy to have a greater capacity to process two or three or more problems at once. It would also be really handy to have a much larger short term memory. One of the challenges of future post-human genetic engineering is to develop DNA sequences that code for brains that can handle more problems at once.

I am expecting the use of genetic engineering on offspring to make easy the expansion of short term memory working set size. Plenty of people have bigger memory working set sizes. We'll be able to compare their genetic sequences to those of lesser minds and identify the best genes to tweak for bigger short term memories. But will we discover genetic variations that increase the ability of human minds to do many tasks at once? Do such variations exist in the human population? Or are the architectural changes needed to allow parallel processing on major problems too big for such genetic variations to come into existence naturally?

Share |      Randall Parker, 2007 January 18 10:57 PM  Brain Limits

Brett Bellmore said at January 19, 2007 4:23 AM:

I think an important question is, do people serialize processes they have some *experience* at performing, in the same way? This test presented people with two novel tasks to perform, and we know that the brain takes tasks that are performed repeatedly, and starts handling them differently from novel tasks.

We do, after all, have a long evolutionary history of walking and talking at the same time. WITHOUT falling flat on our faces, or walking into trees. I suspect walking and driving would be handled similarly. Dialing and driving? I've got my doubts about that. So perhaps this is an argument that phones in cars should require voice dialing.

I'd suggest the researchers spend some time training their subjects to perform these tasks, until they can do them without conscious thought, and THEN see if they're still running into a serial bottleneck.

Nancy Lebovitz said at January 19, 2007 6:43 AM:

I'd also like to see research on the kinds of multitasking people like and/or believe they're good at--I bet there's considerable variation in how various combinations of tasks get handled.

Nordic said at January 19, 2007 10:12 AM:

I would love to see some studies on how we learn to do two things at once - is there a delay so slight we do not percieve it or do we develop different pathways.

A good example is playing a piano. Anyone can pick out a melody with the right hand, but playing even a simple song with both hands is devilishly difficult. Millions of people, however, have developed the ability to play instruments with both hands. What happens in the brain to allow that to happen?

Vince said at January 19, 2007 5:14 PM:

I don't think that walking and driving are handled the same way. Walking is an instinct. Human beings, left alone, will eventually learn how to walk. Driving, however, is a learned skill. Communicating is somewhat in between. Communicating on a cell phone is certainly not instinctual.

To combine two non-instinctual things may well be the problem here. And I don't think high IQ people are exempt from the difficulty. They may be better able to serialize their actions by devoting proper brain time to each one, but the mind just isn't a multi-tasker, I think.

undergroundman said at January 19, 2007 7:15 PM:

I imagine you're right about the short-term memory. For long-term memory, though, could it be that we already have the resources? Some people seem to swear by mnemonics, but I couldn't do much with it. (I suppose I didn't try that hard -- I got the whole 'pictures' lesson; isn't it annoying?)

Gerald Hib bs said at January 20, 2007 7:39 AM:

Yeah, I tried the mnemonics thing too and got to where I could remember a list of 20 things by associating them with a picture based on a number (one is a tree, the word is bus -- picture a bus crashing into a tree.) Didn't take it farther than that as it didn't seem terribly useful. There are some smart drugs out there, I don't use them but they are there, that can do quite a lot with memory formation.

Check out the forums on the subject. It is like going into a forum for steroid using body builders but for the brain. Lots of discussion of "stacks." Makes me wonder if there is anybody out there doing stacks of both kinds of drugs. If they started out strong/smart they must be virtual supermen with the drugs.

The brain is so complex and we still have such a limited understanding. I think it will be possible to build brain/computer interfaces that will allow quite a lot of interesting things but I'm not certain how much we'll be able to overcome our own physical limitations.

For example the whole concept of turning our brains "multi-core" seems like an exceedingly difficult project that is a looooooooong ways off if it can be done at all. I think it more likely we'll see "uploading" before that.

But, since we know that the brain behaves like a muscle and responds to demand by developing the ability to more ably meet the demand I wonder if they did a study of training people to be multi-task if we would see new neuron growth. I would be that one of the advances we'll make is training programs that help keep the brain healthy and expand its ability. Cyber gym programs already exist. Anybody ever use ThinkFast (now defunct I believe) or any of those programs?

Adam said at January 20, 2007 1:28 PM:

Just so you guys know for that driving thing,

I believe that driving while talking on a cell phone is similar to driving while talking to someone next to you.

PBS Nova had an episode a couple of years ago where they talked about this guy who had blindsight, he was blind in one eye but could see motion using that eye.

They explained that the reason he is able to see motion in that eye while not being able to actually see is the brain uses a different part of the brain for motion detection in certain situations.

They used an example of driving a car and the scientist/narrator explained that while he was talking to us (while driving his car) he was actually using that part of his brain to monitor his driving on the road, while he was talking to us.

If you wish to look it up, I believe the title of the episode was "Secrets of the Mind" and if any of you wish, I'm sure I have a recording of it lying around.


Vince said at January 20, 2007 8:46 PM:

That's interesting Adam, but talking on a cell phone is very different than in person communication.

With cell phones, entire channels of communication are cut out, like body language. But the biggest difference is the inability of the person you're talking to on the cell phone to see what you're doing on the road. If a stressful situation comes up, a person next to you will quiet down and wait to complete his thoughts until after the stress has passed. A person on the cell phone has no such benefit, and instead must rely on verbal cues, which further distract the driver who has to give them.

All of that leads to far more stress on the brain, much more going on at one time than can be made comparable to walking and talking. Research even found that the hands-free cell systems that we use in cars today do nothing to stave off accidents, for the reasons I listed above.

teliac said at April 3, 2007 6:23 AM:

the whole process of processing information is, to say least, complex as not to allow the brain to investigate itself. Unless, of course, we have powerful computers(more powerful than the brain) to study the brain
ask yourself: can a human brain invent something more powerful than it??

Nissa said at February 3, 2009 3:14 PM:

I could use some help with regard to this topic. Someone told me a number of years ago that I am a true 'parallel' processor'. To date, I still don't really understand what this means.

I need to have something else going while the activity I am supposed to focus on is occuring. While I was in University, I explained this to my professors, as they tended to interpret my doodling as inattention or boredom. It was one of these professors that dubbed me a parallel processor.

I have always had this. When I was preparing my thesis defense, I came up with the format while I was driving. I scratched it onto a ripped cigarette pack at stop signs. I got the A+. I wrote my actual thesis in front of the tv.

I have recently taken up crocheting while I listen to a speaker. I simply do not absorb the information if I have nothing else to do. (Yes, I am a leg bouncer, a pen twirler/clicker etc). If I don not have this diversion to help me focus, I almost dissociate. Its like when your mind is elsewhere and you read the same paragraph over and over again. That's what happens. I try to listen, I really do, but I end up sort of coming back to reality realizing I had missed almost all of what had just been said.

I would appreciate any help/comments/theories on why I am this way.

Thank you.

Gerard Coppejans said at December 5, 2009 11:51 PM:

I think it's all a matter of training.
Look at tennissers how many taks doesn't theire body perform within a fraction of a second ?
Running for the ball (leggs) , Turning their trunk, putting their arm afterwards (preparation), Look at the position of the opponent, and hit the ball.

Tennis players are trained from the age of 5 or 6 years.
I think that training the multi-tasking system of the brain is best at jong ages because the brain is then still growing.

Gerard Coppejans

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