Shakespeare once wrote that our eyes are the windows of our souls — but might our eyes give away how our minds work as well? In a new study published in The Journal of Neuroscience, a team of researchers found evidence that people who are less patient tend to move their eyes with greater speed. "It seems that people who make quick movements, at least eye movements, tend to be less willing to wait," says Dr. Reza Shadmehr, a professor of biomedical engineering and neuroscience at Johns Hopkins University. Shadmehr and his team of investigators believe an understanding of exactly how our brains evaluate time when weighing our options might illuminate the reasons why decision-making is harder for those with neurological disorders like schizophrenia or for those who have experienced brain injuries.
Examining the Fastest Movements Our Bodies Make
"When I go to the pharmacy and see a long line, how do I decide how long I'm willing to stand there?" Shadmehr asked in a press release. "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?" Based on such questions, Shadmehr and his team explored the possible reasons why some people are willing to wait while others are not. The team hypothesized that patience might be linked to our individual experience of time, and, taking the idea further, the differences in how people move might reflect the differences in how they evaluate time and reward.
To investigate this matter, Shadmehr and his team decided that very simple eye movements, known as saccades, could stand in for other bodily movements. Saccades are quick, simultaneous movements of both eyes in the same direction — they are the motions our eyes make as we focus on one thing and then another. "They occur in just milliseconds," says Shadmehr. "They are probably the fastest movements of the body." Over our lifespans, these fast eye movements evolve, peaking in our teens and then slowing as we age.
In a previous study, Shadmehr and colleagues had used a mathematical theory to show that, in principle, the speed at which people move could be a reflection of the way the brain calculates the passage of time to reduce the value of a reward. Based on that principle, the team enlisted volunteers for the current study and asked them to look at a screen upon which dots would appear one at a time –– first on one side of the screen, then on the other, then back again. As the volunteers looked from one dot to the other, a camera recorded their saccades. The researchers observed a lot of variability in saccade speed among different people but within an individual, there was very little variation — even when that person was tested at different times and on different days. “Some people simply make fast saccades,” concluded Shadmehr.
Do Your Eyes Give You Away?
Next, the team wanted to determine whether saccade speed correlated with decision-making and impulsivity. For this experiment, the volunteers were told to watch the screen again. This time, however, the researchers gave them visual commands to look to the right or to the left. When they responded incorrectly, a buzzer sounded. After becoming accustomed to this procedure, they began a second round of testing, but first the researchers warned them that in some instances, the first command, after an undetermined amount of time, would be replaced by a second command to look in the opposite direction. If they followed each new command immediately, then, they would be sure to be wrong 25 percent of the time.
To pinpoint exactly how long each volunteer was willing to wait to improve his or her accuracy, the researchers modified the length of time between the two commands based on a volunteer's previous decision. If a volunteer chose to wait until the second command, for example, 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.
Comparing the results of the two rounds, the researchers discovered a strong correlation between an individual’s level of patience and the general speed of his or her saccades. In other words, those with the quickest eye movements were also the least patient. The team hypothesized that the way the nervous system evaluates time and reward may be linked to movements and to decision-making. “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 said. These findings, the researchers concluded, suggest that the importance people give to the passage of time may affect the speed with which they move as well as the way they make certain decisions.
Source: Shadmehr R, Choi J, Vaswani P. Fast Eye Movements: a possible indicator of more impulsive decision-making. The Journal of Neuroscience. 2014.