"We are very good at doing many things at once. As you read this column, your brain can also manage your heartbeat, perceive the melody of a song playing on the radio, and send out complicated instructions for drinking a cup of coffee. It can do all that because it is parceled into hundreds of relatively self-contained regions. These regions can work on different tasks at the same time. Yet there are simple jobs—like math problems—that our brains can handle only one at a time. It is as if signals were flying down a 20-lane superhighway, and then the road narrowed to a single lane." says Carl zimmer and explains some recent research in The "Router" in Your Head—a Bottleneck of Processing. Some more excerpts:
"Pashler and his colleagues found that it typically took just under a second for people to respond to the brake lights on the car ahead. But it took longer for them to react if they had responded to a tone within one-third of a second before the lights went on. Pashler found that, on average, the test subjects’ reaction time increased by 0.174 second. That may not seem like a big difference, but if you are driving 65 miles an hour, it translates into an extra 16 feet. That distance can mean the difference between a close call and a high-speed rear-end collision."
"If we don’t have enough time between two tasks, we slow down on the second one—a lag known as the 'psychological refractory period'.....
Each time we perform a task we perform it in three steps. Step 1: Take in information from the senses. Step 2: Figure out what to do in response. Step 3: Carry out that plan by moving muscles. Stanislas Dehaene, chair of experimental cognitive psychology at the College of France, and neuroscientist Mariano Sigman of the University of Buenos Aires wondered where along these steps the traffic jam arises. To find out, they designed new variations on the classic Telford experiments.
In these experiments, subjects had to decide whether a number was higher or lower than 45. In each version of the test, the scientists varied one of the three steps of the thought process to see if they could change the length of the psychological refractory period. Only when they tinkered with step 2—figuring out what response to make—could they produce a change.....
Dehaene now thinks he knows why our thoughts get stuck in bottlenecks: The neurons that take in sensory information send it to a neural network that he and his colleagues call the "router." Like the router in a computer network, the brain’s version can be reconfigured to send signals to different locations. Depending on the task at hand, it can direct signals to the parts of the brain that produce speech, for instance, or to the parts that can make a foot push down on a brake pedal. Each time the router switches to a new configuration, however, it experiences a slight delay."
These, more examples and links in Carl zimmer's article.