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Study shows neural "bottleneck" may limit performance while multitasking

Previous research conducted by Stanford professor Clifford Nass, PhD, has shown that heavy media multitaskers pay a hefty mental price. Now a Vanderbilt study in the Proceedings of the National Academy of Sciences is offering more insight into why our performance suffers when we try to do too many things at once. Ars Technica reports:

The paper focuses on two tasks. Recognizing new information in your surroundings and incorporating it into your view of the world is referred to as "encoding," while reacting to stimuli and making decisions is termed "response selection." They're distinct processes, but they utilize some of the same parts of the brain, so it's possible that the brain can have trouble if asked to perform both of these processes at once or in very close succession. In this study, the researchers used fMRI data to determine whether there is a common bottleneck for both perception and decision making.

Subjects were asked to perform several tasks while inside an fMRI machine. In the first part of the experiment, they had to respond vocally to a tone, respond manually to an image, or perform both of these tasks at once. Not surprisingly, the participants responded faster and more accurately when they only had to concentrate on one task. When the participants had to do both at once, the brain was overloaded; structures that the fMRI revealed to be particularly active at this point were potential bottlenecks for the encoding process.

Then, the researchers performed a similar test to look for bottlenecks in response selection. In these experiments, the participants were quickly presented with one or more letters that they had to recall after fourteen seconds. Here, the overload occurred when they had to remember several letters as opposed to just one; researchers searched for areas of the brain that limited this process.

Findings (subscription required) showed that multiple areas of the brain met the criteria for "bottleneck," which limits both what we can perceive and what we can act on in multitask settings. Researchers determined that a "unified bottleneck," involving the inferior frontal junction, superior medial frontal cortex and bilateral insula, can decrease performance when performing seemingly different tasks.

Previously: A conversation about our evolving relationship with technology and the dangers of multitasking, Is living in an always-on world diminishing our ability to think and work?, Do we have dual-core brains? and Background music may diminish cognitive performance
Photo by Leon Brocard

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