Despite the siren call our our increasingly multimedia, multitasking society, humans seem to behave like old computers with a single-core processor, rather than the latest PCs with multiprocessing.

This is not literally true – our brains are massively parallel, and they can process multiple kinds of information simultaneously. This is why I wrote above about human behavior and not brain processing. To clarify the distinction – our brains can parallel process, but we can only pay attention to one thing at a time. So while multiple subconscious processes are going on at the same time, that part of our brains that pays attention, that manipulates information in our working memories, can only focus on one thing at a time. This stream of attention has peripheral awareness of other things going on, and information on the periphery of our awareness can grab our attention, of course. But there is a certain threshold for this, and it is higher than one might naively think.

But a number of independent lines of research all lead to the same conclusion – we can’t actually pay attention to multiple things at the same time. We may be able to switch back and forth, but the attention any one item gets will suffer.

And yet, people who multitask generally think they are good at it. They are deceiving themselves, it turns out.

Researchers at Stanford University defined two groups of subjects – those who frequently multitask and those who do not. They wanted to find out what skills the multitaskers have the non-multitaskers do not. They tested the two groups with three standard psychological tests of attention. The first test involved showing subjects blue and red rectangles and then having them determine on a subsequent showing if the red rectangles changed orientation – this tests the ability to ignore irrelevant information. The second task involved showing subjects a series of letters and then hitting the button when they see a letter they had seen exactly three letters previously – a test of memory organization. And the third task involved being shown letter/number pairs and then being asked at random to either determine if the letter was a vowel or if the number were odd/even – a test of the ability to rapidly switch between tasks.

This turned out to be one of those wonderful experiments where the experimenters find exactly the opposite of what they expected – the high multitaskers performed significantly worse on all three tasks. This was especially surprising because the researchers chose these tasks based upon the hypothesis that they involved skills useful for multitasking. Further, the high multitaskers thought they were good at multitasking while the low multitaskers thought they were poor at it.

This study reinforces the conclusion that people easily delude themselves. It does not show we are bad at multitasking – it was not designed to test that. Rather, it shows that people who multitask either do so because they think they are good at it when they are not, or they do it because they have to or want to and then rationalize their multitasking by deluding themselves into thinking that they are good at it.

But why are high multitaskers worse at standard tests of attention? This needs further exploration. Perhaps multitasking dulls our mental abilities – we lose the ability to focus, to filter out extraneous information, and to quickly shift our attention to a necessary task. Or – perhaps high multitaskers do so because they naturally have poor attention skills, or don’t recognize the negative impact multitasking has on their performance. Maybe low multitaskers are better able to detect the deleterious effects multitasking has on attention and performance.

Perhaps this should not have been as surprising at it was. We know, for example, that even something as simple as talking on a cell phone has a significantly negative impact on driving performance. It also turns out that this is not related to having one hand on the cell phone, but the fact that the conversation diverts our attention from the road.

We also know that our attention is much more limited than we naively feel. There is, for example, a dramatic phenomenon known as inattentional blindness. Here, for example, is Richard Wiseman’s color changing card trick. There is also this video. Take a look (prior to reading the comments).

The lesson is – don’t multitask. Do not text while you are walking on the street or (ack) driving your car (yes, people do this). Don’t read your e-mail while having a conversation (I admit, I am guilty of this one.) Or (if you are George Costanza) don’t eat, watch TV, and have sex at the same time. If you need to perform a task well, give it your full attention.