When it comes to outward signs of impulsiveness, the eyes have it, scientists at Johns Hopkins say.
Researchers found evidence that people who are less patient and make more impulsive decisions tend to have quicker body movements—something that is evident even in the subtle eye movements they make. They concluded that how an individual values time is expressed in both decision making and motor control.
The research, published this week in The Journal of Neuroscience, attempts to determine why some people are willing to wait for a reward while others are not.
"When I go to the pharmacy and see a long line, how do I decide how long I'm willing to stand there?" asked principal investigator Reza Shadmehr, 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?"
To address the question, the team first asked healthy volunteers to look at a screen upon which dots would appear on one side or the other. A camera recorded their subtle eye movements—known as saccades—as they looked from dot to dot.
The researchers found a lot of variability in saccade speed among individuals but very little variation within individuals. They concluded that saccade speed appears to be an attribute that varies from person to person.
Later, to determine whether saccade speed correlated with decision making and impulsivity, the same volunteers performed a different test. This time, they were given visual commands to look to the right or to the left to see the dot, but were also told that if they followed the command right away, they would be wrong 25 percent of the time. In those instances, after an undetermined amount of time, the first command would be replaced by a second command to look in the opposite direction.
To pinpoint exactly how long each volunteer was willing to wait to improve his or her accuracy on this part of the test, researchers modified the length of time between the two commands based on a volunteer's previous decision. For example, if a volunteer chose to wait until the second command, the researchers increased the time they had to wait each consecutive time until they determined the maximum time the volunteer was willing to wait (only 1.5 seconds for the most patient volunteer). If a volunteer chose to act immediately, the researchers decreased the wait time to find the minimum time the volunteer was willing to wait to improve his or her accuracy.
The tests revealed a strong correlation 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 says. "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."
Shadmehr adds that a better understanding of how the brain evaluates time could shed light on why malfunctions in certain areas of the brain make decision-making harder for those with neurological disorders such as schizophrenia, or for those who have experienced brain injuries.Read more from Hopkins Medicine