Dual-task interference in simple tasks: Data and theory.

Published on Sep 1, 1994in Psychological Bulletin20.85
· DOI :10.1037/0033-2909.116.2.220
Harold Pashler86
Estimated H-index: 86
People often have trouble performing 2 relatively simple tasks concurrently. The causes of this interference and its implications for the nature of attentional limitations have been controversial for 40 years, but recent experimental findings are beginning to provide some answers. Studies of the psychological refractory period effect indicate a stubborn bottleneck encompassing the process of choosing actions and probably memory retrieval generally, together with certain other cognitive operations. Other limitations associated with task preparation, sensory-perceptual processes, and timing can generate additional and distinct forms of interference. These conclusions challenge widely accepted ideas about attentional resources and probe reaction time methodologies. They also suggest new ways of thinking about continuous dual-task performance, effects of extraneous stimulation (e.g.. stop signals), and automaticity. Implications for higher mental processes are discussed. For more than 100 years, psychologists have been interested in people's ability (or inability) to perform two or more activities concurrently. One reason these limitations provoke curiosity is simply that people wonder what is humanly possible. This question has obvious significance for practical problems such as designing interfaces to prevent operators from becoming overloaded or predicting what a pilot can do in an emergency. There is also an important scientific reason to try to understand dual-task performance limitations: Overloading a system is often one of the best ways to figure out what the parts of the system are and how these parts function together. For this reason, studying dual-task interference provides an important window on basic questions about the functional architecture of the brain. For certain of these questions—such as whether human cognitive architecture includes a central processor—dual-task studies may provide the only avenue of study. Ordinarily, people are not aware of having much difficulty performing different activities at the same time unless the tasks are either physically incompatible (e.g., typing and drinking coffee) or intellectually demanding (e.g.. conversing and adding up the check in a restaurant). Casual observation of people's behavior outside the laboratory seems to support this impression: People apparently have conversations at the same time they are driving, read magazines while they run exercise bicycles, chew gum while they walk, and so forth. It might seem, therefore, that one would have to look at rather exceptional activities to find much dual-task interference. Laboratory studies show just the opposite, however: Many pairs of tasks interfere with each other quite drastically, even though they are neither intellectually challenging nor physically incompatible.
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