[extropy-chat] Neural bottleneck found that thwarts multi-tasking
hkhenson at rogers.com
Sun Jan 21 18:27:01 UTC 2007
[It's been interesting lately finding things on one mailing list that
should be shared on others. KH]
Neural bottleneck found that thwarts multi-tasking
René Marois and Paul Dux
Many people think they can safely drive while talking on their cell phones.
Vanderbilt neuroscientists Paul E. Dux and René Marois have found that when
it comes to handling two things at once, your brain, while fast, isn't that
"Why is it that with our incredibly complex and sophisticated brain, with
100 billion neurons processing information at rates of up to a thousand
times a second, we still have such a crippling inability to do two tasks at
once?" Marois, associate professor of Psychology, asked. "For example, what
is it about our brain that gives us such a hard time at being able to drive
and talk on a cell phone simultaneously?"
Researchers have long thought that a central "bottleneck" exists in the
brain that prevents us from doing two things at once. Dux and Marois are
the first to identify the regions of the brain responsible for this
bottleneck, by examining patterns of neural activity over time. Their
results were published in the Dec. 21 issue of Neuron.
"In our everyday lives, we seem to complete so many cognitive tasks
effortlessly. However, we experience severe limitations when we try to do
even two simple tasks at once, such as pressing a button when a visual
stimulus appears and saying a word when a sound is presented. This is known
as dual-task interference," Dux, a postdoctoral research associate in the
Department of Psychology, said. "We were interested in trying to understand
these limitations and in finding where in the brain this bottleneck might
be taking place."
The research is particularly timely, as additional states consider banning
the use of cell phones while driving.
"While we are driving, we are bombarded with visual information. We might
also be talking to passengers or talking on the phone," Marois said. "Our
new research offers neurological evidence that the brain cannot effectively
do two things at once. People think if they are using a headset with their
cell phone while driving they are safe, but they're not because they are
still doing two cognitively demanding tasks at once."
Identifying the information bottleneck responsible for this dual-task
limitation required the use of functional magnetic resonance imaging, or
fMRI, an imaging technology that reveals the brain areas active in a given
mental task by registering changes in oxygenated blood concentration in
these regions. While fMRI is an excellent tool for identifying a particular
area in the brain involved in a given task, it generally provides limited
information about how that area responds over time.
To overcome this limitation, Dux and Marois rapidly sampled brain activity
using fMRI while subjects were performing two demanding tasks. Evaluation
of the data produced by this rapid sampling method allowed them to
characterize the temporal pattern of activity in specific brain areas.
The two tasks consisted of pressing the appropriate computer key in
response to hearing one of eight possible sounds and uttering an
appropriate syllable in response to seeing one of eight possible images.
Different senses and motor responses were enlisted in order to ensure that
any interference between the two tasks was not specific to a particular
sensory or motor modality, but instead originated at a central
The results revealed that the central bottleneck was caused by the
inability of the lateral frontal and prefrontal cortex, and also the
superior frontal cortex, to process the two tasks at once. Both areas have
been shown in previous experiments to play a critical role in cognitive
"We determined these brain regions responded to tasks irrespective of the
senses involved, they were engaged in selecting the appropriate response,
and, most importantly, they showed 'queing' of neural activity--the neural
response to the second task was postponed until the response to the first
was completed," Dux said.
"Neural activity seemed to be delayed for the second task when the two
tasks were presented nearly simultaneously - within 300 milliseconds of
each other," Marois said. "If individuals have a second or more between
tasks, we did not see this delay.
"This temporal delay is the essence of dual-task interference for tasks
that require actions. By using time-resolved fMRI, we can see its signature
in the brain," he continued. "These findings allow us to really now focus
on this set of brain areas and to understand why these areas cannot process
two tasks at once."
The researchers are interested in further exploring what is happening in
the bottleneck to slow performance and believe the work may have future
implications for people performing complex tasks.
"It may be possible to look to the sort of tasks people are going to have
to do in a very complex environment, such as flying a plane, and find out
under what circumstances these tasks may be less vulnerable to dual-task
interference," Dux added.
For the record, neither Marois nor Dux use their cell phones while driving.
"I'm Australian, and it's illegal there, so I'm trained not to," Dux said.
"Even so, I would never do it. Dual-task costs can be up to a second, and
that's a long time when you're traveling at 60 miles per hour."
Source: Vanderbilt University
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