Summary: The speed with which our eyes race through a range of options gives new clues to how we make decisions.
Source: University of Colorado
New research from scientists at the University of Colorado Boulder suggests the eyes really may be the window to the soul – or, at least, the way humans look can reveal valuable information about how they look. make decisions.
The new findings offer researchers a rare opportunity in neuroscience: the ability to observe the inner workings of the human brain from the outside. Doctors could also potentially use the results to one day screen their patients for conditions like depression or Parkinson’s disease.
“Eye movements are incredibly interesting to study,” said Colin Korbisch, a doctoral student in the Paul M. Rady Department of Mechanical Engineering at CU Boulder and lead author of the study. “Unlike your arms or legs, the speed of eye movements is almost completely involuntary. It’s a much more direct measure of those unconscious processes going on in your brain.
He and his colleagues, including researchers from 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 parameters displayed on a computer screen: a brief climb up a steep incline or a longer walk on a flat terrain.
The researchers found that the subjects’ eyes betrayed them: even before they had made their choice, treadmill users tended to move their eyes more quickly when looking at the options they ultimately chose. The more vigorously their eyes moved, the more they seemed to prefer their choice.
“We’ve discovered an accessible metric that will tell you, in just seconds, not just what you prefer, but how much you prefer,” said Alaa Ahmed, lead author of the study and associate professor of mechanical engineering at CU Boulder. .
Ahmed explained that how or why humans make choices (tea or coffee? Dogs or cats?) is notoriously difficult to study. Researchers don’t have many tools with which to easily peer inside the brain. Ahmed, however, thinks our eyes could provide 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 in jerks,” Ahmed said. “That’s when your eyes quickly jump from one point of fixation to another.”
Speed is the key word: saccades usually only take a few tens of milliseconds, making them faster than an average blink.
To find out if these rapid movements give any clues to how humans make decisions, Ahmed and his colleagues decided to hit the gym.
In the new study, the team installed a treadmill on the CU Boulder campus. The study subjects exercised on various inclines for a period of time, then sat in front of a monitor and a high-speed camera that tracked their eye movements.
In front of the screen, they brainstormed a series of options, being given 4 seconds to choose between two choices represented by icons: Did they want to walk 2 minutes at 10% or 6 minutes at 4%? Once done, they returned to the treadmill to feel the burn depending on what they chose.
The team found that the subjects’ eyes went through a marathon of activity in a very short time. As they considered their options, individuals flicked their eyes between the icons, slowly at first, then faster.
“At the start, jerks between the two options were equally vigorous,” Ahmed said. “Then over time that vigor grew and it grew even faster for the option they ultimately chose.”
The researchers also found that the people who made the most hasty decisions — the most impulsive members of the group, perhaps — also tended to move their eyes more vigorously. Once the subjects decided on their choice, their eyes slowed down again.
“Real-time readings of this decision-making process typically require invasive electrodes placed in the brain. Having this variable more easily measurable opens up a lot of possibilities,” Korbisch said.
Diagnose a disease
Glimpses might matter a lot 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 this or that may also break down in people with Parkinson’s disease, a neurological condition in which individuals experience tremors, difficulty moving and other problems.
“Slowed movements are not only a symptom of Parkinson’s disease, but also appear in many mental health disorders, such as depression and schizophrenia,” Ahmed said. “We think these eye movements could be something medical professionals follow as a diagnostic tool, a way to identify the progression of certain diseases.”
The eyes, in other words, could be windows to more than the soul.
About this decision research news
Author: Daniel Strain
Source: University of Colorado
Contact: Daniel Strain – University of Colorado
Image: Image is in public domain
Original research: Access closed.
“The vigor of saccades reflects the rise of decision variables during deliberation” by Colin Korbisch et al. Current biology
The vigor of saccades reflects the rise of decision variables during deliberation
- Saccade vigor increases during deliberation, reflecting decision variables
- The strength of the saccade indicates the degree of subjective preference
- The rate of change in vigor increases with the difference in value of the options
- The relative vigor of individuals correlates with the average deliberation time
During deliberation, as we quietly consider our options, neural activities representing decision variables that reflect the quality of each option increase in various regions of the cerebral cortex.
If the options are represented visually, we make jerks, concentrating the gaze on each option. Does the kinematics of these saccades reflect the state of the decision variables?
To test this idea, we engaged human participants in a decision-making task in which they considered two demanding options that required walking different distances and gradients.
As they deliberated, they jerked between symbolic representations of their options. These deliberation period saccades had no bearing on the effort they would later exert, but the speeds of the saccades increased progressively and differentially: the rate of climb was faster for the saccades to the option which they later indicated as their choice. Indeed, the rate of increase encodes the difference in subjective value of the two options.
Importantly, the participants did not reveal their choice at the end of the deliberation, but instead waited for a period of delay, and finally expressed their choice by making another jerk.
Remarkably, the vigor of this saccade dropped to baseline and no longer encoded subjective value. Thus, the vigor of the jerks seemed to provide a real-time window to the otherwise hidden process of evaluating options during deliberation.
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