Why the Brain Reacts to Surprises With Temporarily Blindness

by Tanya Thomas on  March 14, 2010 at 8:14 AM Research News
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 Why the Brain Reacts to Surprises With Temporarily Blindness
While we can manage to read the newspaper in a bus with loud music, a sudden fire alarm can easily snatch away our attention from the paper to the blaring sound. Now, researchers have shown why we may be temporarily blinded by surprises.

The study from Vanderbilt University has for the first time revealed how our brains coordinate these two types of attention.

"The simple example of having your reading interrupted by a fire alarm illustrates a fundamental aspect of attention: what ultimately reaches our awareness and guides our behaviour depends on the interaction between goal-directed and stimulus-driven attention. For coherent behavior to emerge, you need these two forms of attention to be coordinated. We found a brain area, the inferior frontal junction, that may play a primary role in coordinating these two forms of attention," Nature quoted Rene Marois, co-author of the study, as saying.

The researchers were also interested in what happens to us when our attention is captured by an unexpected event.

"We wanted to understand what caused limitations in our conscious perception when we are surprised. We found that when shown a surprise stimulus, we are temporarily blinded to subsequent events," said Christopher Asplund, primary author of the new study.

In the study, researchers asked individuals to detect the letter "X" in a stream of letters appearing on a screen while their brain activity was being monitored using functional magnetic resonance imaging, or fMRI.

Occasionally, an image of a face would unexpectedly interrupt the stream. he surprise caused the subject to completely miss the "X" the first couple of times, despite the fact they were staring directly at the part of the screen on which it appeared.

They were eventually able to identify it as successfully as when there was no surprise.

The researchers used fMRI and found that the inferior frontal junction, a region of the lateral prefrontal cortex, was involved in both the original task and in the reaction to the surprise.

"What we think might be happening is that this brain area is coordinating different attention systems - it has a response both when you are controlling your attention and when you feel as though your attention is jerked away," said Asplund.

Surprise stimuli trigger what is known as the orienting response in which the heart rate increases, the nervous system is more aroused and we pay intense attention to a new item in our environment.

Described by Pavlov in dogs, the orienting response allows one to determine if a new item is a good thing, such as food, or a threat, such as a predator, and to react accordingly.

"What we show is the dark side or negative impact of the orienting response. We found it blinds you to other events that can occur soon after the presentation of the surprise stimulus," Marois said.

The researchers hypothesize that we may be temporarily blinded by surprise because the surprise stimulus and subsequent response occupies so much of our processing ability.

The study was published in Nature Neuroscience.

Source: ANI

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