Eye movement holds clues to decision-making process

Unlike your arms or legs, the speed of eye movements is almost totally involuntary, and the study shows that it can hint at the decision-making process

 A brown eye (photo credit: Wikimedia Commons)
A brown eye
(photo credit: Wikimedia Commons)

The eyes, as it is commonly said, may really be the window to the soul – or, at least, how humans dart their eyes may reveal valuable information about how they make decisions. 

New research led by scientists at the University of Colorado (CU) at Boulder offered researchers a rare opportunity in neuroscience – the chance to observe the inner workings of the human brain from the outside. Doctors could also potentially use the results eventually to screen their patients for illnesses like depression or Parkinson’s disease.

Doctoral student Colin Korbisch and his colleagues, including researchers at Johns Hopkins University in Baltimore published their findings in November in the journal Current Biology under the title “Saccade vigor reflects the rise of decision variables during deliberation.”

“Eye movements are incredibly interesting to study,” said Korbisch who was the lead author of the study. “Unlike your arms or legs, the speed of eye movements is almost totally involuntary. It’s a much more direct measurement of these unconscious processes happening in your brain.” 

In the study, the team asked 22 people to walk on a treadmill and then choose between different settings displayed on a computer screen, either a brief walk up a steep grade or a longer walk on flat ground. 


They discovered that the subjects’ eyes gave them away: Even before they made their choices, the treadmill users tended to move their eyes faster when they looked toward the options they ended up choosing. The more vigorously their eyes moved, the more they seemed to prefer their choice. 

“We discovered an accessible measurement that will tell you, in only a few seconds, not just what you prefer but how much you prefer it,” said Alaa Ahmed, senior author of the study and associate professor of mechanical engineering at CU.

Ahmed explained that how or why humans make choices like tea or coffee or dogs or cats that are very difficult to study. Researchers don’t have many tools that will easily allow them to peer inside the brain. But Ahmed believes that our eyes could provide a glimpse into some of our thought processes. She’s particularly interested in a type of movement known as a “saccade.” The primary way our eyes move is through saccades, Ahmed said. “That’s when your eyes quickly jump from one fixation point to another.” Saccades usually take just a few dozen milliseconds to complete, making them faster than an average blink. 

How did the researchers conduct the study?

To find out if these darting motions give clues about how humans come to decisions, Ahmed and her colleagues decided to go to the gym. Study participants exercised on various inclines for a period of time and then sat down in front of a monitor and a high-speed, camera-based device that tracked their eye movements. While at the screen, they considered a series of options, getting four seconds to pick between two choices represented by icons: Did they want to walk for two minutes at a 10% grade or for six minutes at a four-percent grade? Once done, they returned to the treadmill to feel the burn based on what they chose. 

The team found that the subjects’ eyes underwent a marathon of activity in just a short span of time. As they considered their options, the individuals flitted their eyes between the icons, first slowly and then faster. “Initially, the saccades to either option were similarly vigorous,” Ahmed said. “Then, as time passed, that vigor increased and it increased even faster for the option they eventually chose.”

The researchers also discovered that people who made the hastiest decisions – the most impulsive members of the group, perhaps – also tended to move their eyes more vigorously. Once the subjects decided on their pick, their eyes slowed again. 

“Real-time read-outs of this decision-making process typically require invasive electrodes placed into the brain. Having this more easily measured variable opens a lot of possibilities,” Korbisch added 

Flicks of the eye could matter for a lot more than understanding how humans make decisions. Studies in monkeys, for example, have suggested that some of the same pathways in the brain that help primates pick between this or that may also break down in people with Parkinson’s, the progressive, incurable neurological illness in which individuals experience tremors, difficulty moving and other problems.

“Slowed movements aren’t a symptom just of Parkinson’s but also appear in a lot of mental health disorders such as depression and schizophrenia,” Ahmed said. “We think these eye movements could be something that medical professionals track as a diagnostic tool, a way to identify the progress of certain illnesses.” Eyes, in other words, could be windows to a lot more than just the soul.