New research led by scientists at the University of Colorado Boulder suggests that the eyes may actually be the window to the soul, or at least how humans squint may reveal valuable information about how they make decisions.
The new findings offer researchers a rare opportunity in neuroscience: the chance to observe the inner workings of the human brain from the outside. Doctors could also use the results to one day screen their patients for diseases such as depression or Parkinson’s disease.
“Eye movements are incredibly interesting to study,” said Colin Korbisch, a doctoral student in CU Boulder’s Paul M. Rady Department of Mechanical Engineering and lead author of the study. “Unlike arms or legs, the speed of eye movements is almost entirely involuntary. It’s a much more direct measure of these unconscious processes going on in your brain.”
He and his colleagues, including researchers at Johns Hopkins University in Baltimore, published their findings in November in the journal Current Biology.
In the study, the team asked 22 human subjects to walk on a treadmill and then choose between different configurations displayed on a computer screen: a short walk up a steep incline or a longer walk for a flat ground.
The researchers found that the subjects’ eyes gave them away: Even before they made their choices, treadmill users tended to move their eyes faster when looking toward the options they ended up choosing. The more vigorously their eyes moved, the more they seemed to prefer his choice.
“We’ve discovered an accessible measurement that will tell you, in just a few seconds, not just what you prefer, but how much you prefer it,” said Alaa Ahmed, lead author of the study and associate professor of mechanical engineering at CU Boulder.
Bloody eyes
Ahmed explained that how or why humans make decisions (tea or coffee? Dogs or cats?) is notoriously difficult to study. Researchers don’t have many tools that allow them to easily look inside the brain. Ahmed, however, believes that our eyes could offer insight into some of our thought processes. She is particularly interested in a type of movement known as a “saccade”.
“The main way our eyes move is through saccades,” Ahmed said. “That’s when your eyes quickly jump from one fixation point to another.”
Fast is the key word: saccades typically take a few dozen milliseconds to complete, making them faster than the average blink.
To find out if these throwing motions provide clues about how humans make decisions, Ahmed and his colleagues decided to go to the gym.
In the new study, the team set up a treadmill on the CU Boulder campus. Study subjects exercised at various inclines for a period of time and then sat in front of a monitor and a high-speed camera-based device that tracked their eye movements. While on the screen, they pondered a series of options, getting 4 seconds to choose between two options represented by icons: did they want to walk for 2 minutes at a 10% grade or for 6 minutes at a 4% grade? Once done, they returned to the tape to feel the burn based on what they chose.
The team found that the subjects’ eyes underwent a marathon of activity in a short time. While considering their options, individuals moved their eyes between the icons, first slowly and then faster.
“Initially, saccades to either option were equally vigorous,” Ahmed said. “Then, as time went on, that vigor increased and increased even more rapidly for the option they ultimately chose.”
The researchers also found that people who made the most hasty decisions—perhaps the most impulsive members of the group—also tended to move their eyes more forcefully. Once the subjects decided on their choice, their eyes slowed down again.
“Real-time readouts of this decision-making process typically require invasive electrodes placed in the brain. Having this easier-to-measure variable opens up a lot of possibilities,” Korbisch said.
Diagnosis of the disease
Glimpses could matter far more than understanding how humans make decisions. Studies in monkeys, for example, have suggested that some of the same brain pathways that help primates choose between this and that may also break down in people with Parkinson’s, a neurological disease in which people experience tremors, difficulty moving and other problems.
“Slow movements are not just a symptom of Parkinson’s, but also appear in many mental health disorders, such as depression and schizophrenia,” Ahmed said. “We think these eye movements could be something that medical professionals follow as a diagnostic tool, a way to identify the progress of certain diseases.”
The eyes, in other words, could be windows to much more than just the soul.
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