There are two Discovery Labs related to dual-task interference. It is best to complete this Discovery Lab first.

Suppose you are playing a video game where you are fighting a villain. As part of the game, you must choose a button on the left side of the keyboard to shoot a gun or cannon, depending on the character that appears on the screen, and you must also choose a button on the right side of the keyboard to select a button to perform a block or initiate a shield, depending on what type of weapon you are attacked with. Suppose also that choosing the wrong weapon or the wrong shield had dire consequences, so you had to be careful about what buttons you chose. How would your performance on this game be affected by the speed at which events occur? Whether or not you have played this type of game, you can probably guess that your performance on a given task will be worse when that task must be performed at the same time or soon after another task, and that if the tasks occur very far apart in time, they will be relatively easy to complete well.

Psychologists have tested this hypothesis using what is known as the perceptual refractory period (PRP) paradigm. In this paradigm, participants are presented with two stimuli at varying stimulus onset asynchronies (SOAs). Sometimes one task is done right after the other, sometimes there is a delay. Response times (RTs) to the second task are then examined as a function of SOA. If two tasks can be done at the same time, then no effect of SOA will be observed on response times for the second task. If, however, one task can’t start until the next is finished, response times for the second task will be slow when the second task has to be completed at almost the same time as the first task.