June 07, 2004
Brains Can Not Process Two Tasks In Parallel

Faced with two tasks to do at once the brain appears to switch back and forth between them rather than thinking about them in parallel.

It's readily apparent that handling two things at once is much harder than handling one thing at a time. Spend too much time trying to juggle more than one objective and you'll end up wanting to get rid of all your goals besides sleeping. The question is, though, what makes it so hard to process two things at once?

Two theories try to explain this phenomenon: "passive queuing" and "active monitoring." The former says that information has to line up for a chance at being processed at some focal point of the brain, while the latter suggests that the brain can process two things at once it just needs to use a complicated mechanism to keep the two processes separate. Recent research from MIT points to the former as an explanation.

Yuhong Jiang, Rebecca Saxe and Nancy Kanwisher, in a study to be published in the June issue of Psychological Science, a journal of the American Psychological Society, examined the brain activity involved in multitasking. They gave people two simple tasks. Task one was identifying shapes, and for some subjects, task two was identifying letters, for others it was identifying colors. The subjects were forced to switch from one task to the other in either one and a half seconds or one tenth of a second. When they had to switch faster, subjects would take as much as twice as long to respond than when switching more slowly.

Using MRI technology, Jiang, Saxe and Kanwisher examined subjects' brain activity while performing these tasks. They observed no increase in the sort of activity that would be involved in keeping two thought processes separate when subjects had to switch faster. This suggests that there are no complicated mechanisms that allow people to perform two tasks at once. Instead, we have to perform the next task only after the last one is finished.

I am looking forward to the day when it becomes possible to genetically engineer minds to have bigger working memories and other cognitive enhancements. Given that some people have larger working memories than others have once we find out the cause of that difference we will probably be able to genetically engineer offspring to have bigger working memories and perhaps to do the same for ourselves. But abilities that do not already exist (such as some types of parallel processing) will be more difficult to add. But if enhancements for parallel processing could be developed it would be very handy. The ability to do productive work while carrying on a demanding conversation would be particularly useful.

Share |      Randall Parker, 2004 June 07 01:49 PM  Brain Limits

Fly said at June 7, 2004 10:48 PM:

Interesting Randall.

Supposedly older people have significantly more difficulty multi-tasking than do the young. They perform about the same as the young when performing a single task but much poorer when splitting attention over multiple tasks. (Hmmm, did artificially increasing dopamine levels in old brains restore multi-tasking ability?)

So does task switching just put more stress on brains, so old brains with less extra capacity do worse? How would one identify an old brain? Fewer new neurons? Fewer synaptic connections? Weaker firing? Less neural transmitter? Fewer receptors? Less metabolically efficient? Do old brains look different under imaging? (I seem to remember shrinkage of gray tissue in some areas.)

Bob Badour said at June 8, 2004 6:31 PM:

More tartar build-up!

Jody said at June 14, 2004 8:14 AM:

In all seriousness, I'm not certain that we want active parallel processing (as opposed to the more passive kind like walking and chewing gum). I strongly suspect an increases in the number of people who can consciously perform parallel processing (or true multitasking) will coincide with an increase in the number of people with multiple personalities.

Really, if you have more than one executive thought process, how is this different from having multiple personalities?

aB said at October 11, 2006 7:26 AM:

What about multi-tasking in things like music? Actively following multiple audible lines simultaneously requires great concentration and memory; perhaps some might argue that this is not true multi-tasking, be that the stimuli originate from a common source or a common thought type or what have you. However, anyone that has given it a try or has mastered it could easily argue to the contrary. A study involving brain imaging, variously voiced fugues and amateur/expert musicians would be terribly interesting and insightful. Does anyone know if this has been done in relation to multi-tasking capabilities of the brain?

Bria said at February 2, 2008 12:36 PM:

This article helped me so much with my science project. Wonderful details and a great job putting this article together. Lots of love to you.

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