Researchers emphasize there are very few circumstances in which you can do two things at once without cost (relative to doing each on its own). Yet some drivers sneak a look at their phone while on the road, and some students have the television playing while they complete an assignment.
Why? One possibility is that they don’t understand the cost of multi-tasking very well. A new study (Finley, Benjamin, and McCarley, 2014) investigated that possibility.
Subjects initially practiced a tracking task: a small target moved erratically on a computer screen and the subject was to try to keep a mouse cursor atop it.
Interleaved with practice on the tracking task, subjects practiced a standard auditory N-back task: they heard a series of digits (one every 2.4 seconds) and were asked to say whether the digits matched the one spoken 2 digits earlier (or in other versions of the task, 1 digit or 3 digits earlier).
After a total of 3 phases of practice for each task, subjects were told that they would try to do both tasks at the same time. They were told to prioritize the tracking task; just as a driver must keep the car in the lane, they should do their best to keep the cursor near the target, but they should do their best on the N-back task.
Then subjects got feedback on their performance on the three phases of tracking task (expressed as percent time they had the cursor on the target) and they were asked to predict their performance on the tracking task when simultaneously doing the N-back task.
The results showed a significant drop in tracking performance when subjects had to do the N-back task at the same time. What did subjects predict?
Subjects did predict a decrement. What they could not do was predict the size.
Read more at http://www.danielwillingham.com/1/post/2014/03/what-people-know-about-the-cost-of-multitasking.html