Distinguishing evidence accumulation from choice confidence in neural signatures of perceptual decision making

In EEG recordings during a contrast discrimination task, centro-parietal positivity (CPP) amplitude is reduced for validly cued choices (80% validity), even after matching for confidence.

• Why it matters: CPP is often treated as sensory evidence accumulation, but it also scales with subjective confidence, leaving open whether it reflects confidence instead of evidence.
• What they did: Participants performed a contrast discrimination task with predictive cues at 80% validity while EEG was recorded; cue validity was used to shift prior expectations and separate confidence from cumulative evidence.
• The result: Valid cues increased response speed, accuracy, and confidence, yet pre-response CPP amplitude decreased for validly cued choices and the reduction persisted when confidence was matched, supporting CPP as an evidence accumulation signal linked to both decisions and confidence.

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