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How Does Multitasking Affect Memory?

Posted: 04/27/10 09:42 AM ET

Back in the 1970s, a guy named Jerry Fodor expounded an arcane concept called the computational theory of mind (CTM). Put very crudely, it says the mind creates consciousness through information processing using its own language and rules. The theory, which Fodor has since abandoned as incomplete and psychologist Steven Pinker has taken up, isn't a metaphor, as both have pointed out time after time. It envisions the mind as actually executing information processing. The human mind is far superior to a mere computer; the very existence of computers is evidence of this.

Too late, said we in the general public. "Computation" is pretty much the same word as "computer," so we like the metaphor. It's the only way we can wrap our computers around your theory. As we came to see computers as a representation of our minds, other metaphors came hard and fast. Memory retrieval is like random-access memory (RAM) accessing a hard drive. Binary encoding of an image is like the way we translate an odor into the scent experience of a flower.

Say, our minds really are like computers, we agreed. Let's see what it takes to make them crash.

It's here another computer term we filched, multitasking, made the leap from metaphor to reality. Originally coined in the mid-'60s to describe a central processing unit's (CPU) ability to carry out more than one process simultaneously, multitasking has come to describe the reality of post-dot-com life. In an ironic twist, the computer, which has served as a metaphor for the functioning of our minds, has come to manipulate our minds' functioning.

Right now you have your Web browser displaying this HuffPo page, plus you probably have your e-mail client open, a Word doc up for work and maybe iTunes on shuffle. The joke is that your computer is actually multitasking; all of these applications are running simultaneously. You, however, are not multitasking and your computer knows it. In a windowed interface, only one window can be prominent at a time, and it overlaps idling windows. Yet, a mouse click is all it takes to move from window to window, introducing different information each time.

Our brain is equipped to handle this rapid shift from window to window, but not well, and nowhere is the futility of multitasking more apparent than in its effects on memory.

The human mind can shift rapidly between tasks, on the order of a few hundred milliseconds. Recent research has uncovered supertaskers, the 2.5 percent of the population who are better than everyone else at texting and driving. But the average mind prefers something closer to a second or two between changes in input. The faster this shift, the less sense we can make of the information.

Functional imaging studies have uncovered a culprit, a kind of flabby region of the brain called the posterior lateral prefrontal cortex (pLPFC). This region, a sort of initial routing hub for information inputs, sends stimuli to their proper centers for processing and storage. It's also been shown to create a (metaphorical) bottleneck when it's bombarded by information.

As pieces of information arrive, the pLPFC puts them in a queue rather than processing them simultaneously. When intervals between information inputs are short, say around 300 milliseconds, this routing hub actually slows down. When confronted with several stimuli, it queues two for processing and ignores the rest.

In the meantime, we're still taking in information, but it's slipping past the pLPFC hub and into the striatum, which is responsible for habit learning, like driving a car or finding letters on a keyboard. Habit learning requires so little conscious thought that we tend to attribute its functions to our limbs and digits, which seem to carry out tasks on their own.

Unfortunately, things like holding a conversation and absorbing the text of an article require an entirely different type of learning, called declarative memory. This type, governed by a different region of the brain, creates coherent meaning out of words on a screen or numbers in an equation. If the pLPFC is busy processing other information, then the page we scanned, the bit of music we listened to, the question we were just asked, essentially slips past to the striatum. When we attempt to recall the information, it's not where it's supposed to be. In effect, the information came in, but it wasn't learned. It's the reason we're insulted when a person we're speaking to checks his BlackBerry while we're talking. We've entered into competition for the person's attention and, for the time being, we've lost.

Such is the curse of multitasking; we are bombarded with more information than ever before, yet we make less use of it than we ever have, too. Researchers have consistently drawn the same conclusion: multitasking is counterproductive and exhausting. Slllloooowwww dooooowwwwwn.

Josh Clark is a writer and blogger for He is also co-host of the podcast, Stuff You Should Know, available on iTunes.