Eye movement speed linked to impulsive decision making
One of the most frustrating things about shopping in a grocery store can be the long lines at the cash register. Do you stand there and wait for the line to go down? Or do you join another line that looks quicker? According to new research, decisions such as this may be dependent on the speed of our eye movements.
In a study published in The Journal of Neuroscience, researchers from Johns Hopkins University in Maryland found that people who are less patient are more likely to have faster eye movements.
The investigators say their findings may provide insight into why abnormalities in certain areas of the brain make decision making more challenging for people who have suffered brain injuries or who have neurological disorders, such as schizophrenia.
According to the investigators, previous research from the team suggested that how a person moves may be an indicator of how the brain works out the time frame in which to reduce the value of a reward. For example, when a person determines how long they should stand in line to get their groceries.
For this study, the researchers wanted to see whether differences in eye movements, in place of other body movements, could reflect differences in how a person assesses time and reward.
Saccade speed 'varies from person to person'
The research team monitored eye movements, known as saccades, of healthy volunteers.
Researchers say the speed of our eye movements may determine our level of patience.
Reza Shadmehr, professor of biomedical engineering and neuroscience at Johns Hopkins University and lead researcher, explains that saccades are the motions the eye makes when we switch focus between objects.
He notes that saccades are the fastest movements in the body, occurring in milliseconds. Saccades are at their fastest during teenage years, but they slow down as a person ages.
The volunteers were asked to look at a screen, where a series of dots appeared one at a time. They first appeared on one side of the screen, then the other, before flicking back and forth to each side.
Using a camera to record the participants' saccades, the investigators found that over all participants, saccade speed varied significantly. However, in each individual participant, saccade speed appeared to be consistent - leading the team to believe that the speed of eye movement varies from person to person.
Testing the participants' patience
The research team then conducted another experiment to determine whether saccade speed is associated with impulsivity and decision making.
This also involved the volunteers viewing the screen with the dots. For this experiment, they were instructed to look left or right. A buzzer sounded if they failed a command.
Once the participants were used to this part of the experiment, they were told that if they followed the first commands in the next testing round, they would be incorrect 25% of the time.
They were also told that in the instances they were wrong, after an undisclosed amount of time, the first command would be taken over by a second command to look in the opposite direction.
The investigators changed the length of time between these two commands in order to identify the length of time participants would be willing to wait to improve their test accuracy.
For example, the researchers explain that if a participant chose to wait until the second command, the time the volunteers had to wait would be increased every time until they chose to answer the first command.
Strong link between saccade speed and impulsivity
On comparing the participants' saccades to impulsivity, the investigators found that the speed of their eye movements closely correlated with their level of patience.
"It seems that people who make quick movements, at least eye movements, tend to be less willing to wait," Prof. Shadmehr says, adding:
"Our hypothesis is that there may be a fundamental link between the way the nervous system evaluates time and reward in controlling movements and in making decisions. After all, the decision to move is motivated by a desire to improve one's situation, which is a strong motivating factor in more complex decision making, too."
Dr. Pavan Vaswani, of the department of neuroscience at Johns Hopkins School of Medicine and co-author of the study, told Medical News Today that their findings may help to diagnose some medical conditions.
"Changes in impulsivity are associated with a number of medical conditions, such as schizophrenia, depression and substance abuse, so understanding impulsivity is potentially useful to the diagnosis of these disorders and evaluation of treatments," he says.
"Impulsivity is usually assessed via questionnaires that ask, for example, if you tend to make up your mind quickly, act without thinking, plan for the long term, etc. Eye movements may provide a more direct, quantitative way to assess impulsivity."
Dr. Vaswani added that the research team plans to conduct further studies looking at eye movements in patients with neurological disorders, such as Parkinson's disease.
Medical News Today recently reported on a study suggesting that the brain is able to classify images that are seen for only 13 milliseconds.
Written by Honor Whiteman
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