Hal Blumenfeld once got out of a pool and couldn’t find his watch. He was certain he’d left it at the edge where he entered. After searching, he discovered it at the opposite end—moved there by his own hand while swimming, with no memory of doing so.
“I had no idea that I had done that,” says Blumenfeld, a professor of neurology at Yale School of Medicine.
More than a century of debate, settled in a puzzle game
The incident stayed with him. Years later, it inspired a study published in PNAS Nexus, the first to examine the brain signals behind conscious awareness of our own actions. The work resolves a long-standing dispute between psychologists William James and Wilhelm Wundt from the late 19th century.
James claimed awareness of action comes after movement, through sensory feedback. Wundt believed it arises from the brain’s planning before any sensation occurs. Neither could prove their argument—until this research.
David S. Jin, a former PhD student in Yale’s Interdepartmental Neuroscience Program and now a postdoctoral fellow at the University of Alabama at Birmingham, created an experiment to test the theories. He used the sliding block puzzle game Rush Hour, where players shift toy cars and trucks to clear a path for a main vehicle to exit. Participants played while watching background videos they were instructed to memorize. The game paused periodically, asking them to identify their last move and rate their confidence.
Correct answers with high confidence were labeled “aware.” Incorrect answers with low confidence were “unaware.” The design mirrored the autopilot moments people experience, like driving a familiar route and suddenly realizing they don’t recall the last few miles.
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The team measured brain activity using electroencephalography (EEG) in 67 participants. Awareness of action didn’t depend on a single signal. Instead, two distinct processes worked together: a motor-planning signal called the pre-movement positivity, which was stronger when participants were aware of their moves, and a sensory processing signal called the N140, linked to bodily sensation, which also increased during aware trials.
“It turns out James and Wundt were both right,” Blumenfeld says. “Both the planning- and perception-related signals are stronger when we’re aware of what we do.”
Boredom, fatigue, and the cost of constant awareness
The study revealed an unexpected third factor. As participants progressed, their pupil diameter shrank—a sign of declining alertness. Awareness of their actions dropped in sync.
“As the task continued, participants grew more bored, more tired, and more distracted,” Blumenfeld explains. “Their pupils shrank, and they became less aware of their actions.”
This suggests unawareness isn’t just a malfunction. It may serve a purpose, letting the brain save energy by ignoring routine tasks. A musician playing a complex piece couldn’t function if they had to consciously focus on every note. The same applies to daily habits like brushing teeth or typing an email.
For Jin, the findings hit close to home. As someone with epilepsy, he’s had seizures where he’s held conversations or played piano without remembering afterward. “The ability to perform complex actions yet not recall them is fascinating,” he says.
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The brain signals identified aren’t just theoretical. They’re disrupted in Parkinson’s disease, schizophrenia, and after strokes—conditions where impaired action awareness complicates diagnosis, recovery, and legal questions about intent. While thousands of studies have explored perceptual awareness, this is the first to systematically study awareness of action.
“It opens up a whole new area of research,” Blumenfeld says. “The field just expanded significantly.”
The lab’s next step involves functional magnetic resonance imaging (fMRI) to examine deeper brain regions inaccessible to surface EEG. Jin admits the results surprised him. He expected a single, clear signal explaining action awareness. Instead, he found multiple signals working in concert.
“I thought I’d find one definitive signal,” he says. “But it was more like a team effort—signals from different cognitive areas all contributing at once.”
The research received support from the National Institutes of Health and Yale University, along with funding from the Mark Loughridge and Michele Williams Foundation and the Betsy and Jonathan Blattmachr Family. The findings could help improve understanding of how organs repair themselves after injury by revealing the brain’s role in monitoring physical actions.