Perceptual decision
How the Brain Tracks Choices When Things Are Unclear
Open access · cc by · source: Europe PMC
A brain wave signal tracks how uncertain we are during decisions, regardless of what we are looking at.
Key findings
They discovered that a brain signal called the late positive potential, measured between 400 to 700 ms after a stimulus appears, reliably tracks how ambiguous an image is. This signal was strongest for clear, unambiguous images and decreased as morphs became more ambiguous, showing similar patterns for both facial expressions and animal categories. Crucially, the signal predicted reaction times and subjective confidence, but it was strongest when the task instructions actively required participants to judge the ambiguous features.
Methodology
To study decision-making, the researchers recorded EEG brain activity from 16 participants while they categorized morphed faces that ranged from happy to fearful. They also tested 11 participants on angry-to-disgusted faces and cat-to-dog morphed animals to see if the brain response was general. Finally, they had 16 different participants perform tasks with varying instructions to see how top-down goals affect this neural signal.
Limitations
While the study shows a clear link between brain activity and decision uncertainty, it cannot prove a direct causal relationship because it is an observational EEG study rather than an intervention. The sample sizes were relatively small, with only 11 to 16 participants per EEG task group, which limits how easily these findings can be generalized to the broader population. Additionally, because the tasks utilized simple categorization of static, artificial morphs, the results may not translate directly to complex, real-world decisions under ambiguity.
How this study connects
Role on claims
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The late positive potential (LPP) between 400 and 700 ms tracks perceptual decision-making by decreasing in amplitude as stimulus ambiguity increases.
Evidence for the claim as stated.
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