Individuals who make impulsive decisions tend to have quicker body movements. In fact, even the most subtle eye movements can reveal whether a person is feeling impulsive, according to a new study at Johns Hopkins University in Baltimore, Md.
The findings, published in The Journal of Neuroscience, also reveal how both decision making and motor control are linked to how a person values his or her time.
“When I go to the pharmacy and see a long line, how do I decide how long I’m willing to stand there?” asked lead researcher Reza Shadmehr, Ph.D., professor of biomedical engineering and neuroscience at Johns Hopkins.
“Are those who walk away and never enter the line also the ones who tend to talk fast and walk fast, perhaps because of the way they value time in relation to rewards?”
For the study, participants were asked to look at dots as they appeared on either side of a screen. A camera recorded their subtle eye movements—known as saccades—as they watched the dots.
The results showed a significant amount of variability in saccade speed between individuals but very little variation within individuals. The researchers concluded that saccade speed appears to be a trait that varies from person to person.
Next, the volunteers performed a test to determine whether saccade speed was connected to decision making and impulsivity.
Participants were given a visual command to look to the right or to the left to see the dot. However, they were also told that if they followed the command right away, they would be wrong 25 percent of the time, as a second command might be given to look in the opposite direction.
To determine exactly how long each participant was willing to wait to improve his or her accuracy on the test, researchers adapted the length of time between the two commands based on the participants’ previous behavior.
For example, if a participant chose to wait until the second command was given, the researchers increased the waiting time until they determined the maximum time the volunteer was willing to wait.
On the other hand, if a volunteer chose to act immediately (without waiting for the second command), the researchers shortened the waiting time to find out the minimum time the volunteer was willing to wait to improve his or her accuracy.
The findings showed a strong connection between saccade speed and decision-making.
“It seems that people who make quick movements, at least eye movements, tend to be less willing to wait,” Shadmehr said.
“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.”
A better understanding of how the brain evaluates time could offer insight into why malfunctions in certain areas of the brain make decision-making harder for those with schizophrenia or brain injuries, added Shadmehr.
Source: Johns Hopkins