P300 ERP
Definition
A positive-going scalp electrical potential peaking approximately 300 ms after presentation of a significant, infrequent, or unexpected stimulus. Used in EEG-based concealed-information testing (Brain Fingerprinting / BEOS) as a marker of stimulus recognition.
- Peak latency
- Approximately 300-600 ms post-stimulus
- Signal type
- Positive scalp EEG deflection
- Application
- Concealed information test (Brain Fingerprinting, BEOS)
- Records
- Multi-channel scalp EEG, often centro-parietal sites
Common questions
Why is the P300 controversial as courtroom evidence?+
It measures recognition, not guilt. A P300 response shows the subject's brain registered a probe item as familiar, but familiarity can come from media exposure, investigator leakage, or innocent association with the crime scene rather than participation in the crime.
How does P300 testing differ from a polygraph?+
A polygraph tracks autonomic arousal (heart rate, skin conductance, respiration) during direct questioning, while P300 concealed-information testing presents probe and irrelevant stimuli and reads a specific electrophysiological recognition marker, sidestepping the countermeasure of controlled breathing that undermines polygraphs.
Related terms
- AI Act Article 5(1)(F)
- The EU AI Act prohibition on AI systems that infer emotions, intentions, or characteristics from biometric data in law-enforcement and related contexts....
- BEOS / Brain Fingerprinting
- Lawrence Farwell's EEG-based method using the P300 event-related potential to detect concealed knowledge of crime-relevant items. Addressed by the Indian Supreme Court...
- BOLD Signal
- Blood-oxygen-level-dependent signal; the measure in fMRI that captures changes in the ratio of oxyhaemoglobin to deoxyhaemoglobin as a proxy for neural activity....
- Cephos Corporation
- A US company that offered commercial fMRI lie-detection services from approximately 2006. Its technique was excluded from evidence in US v. Semrau...
- Daubert Standard
- The US federal evidentiary standard (Daubert v. Merrell Dow Pharmaceuticals, 1993) requiring that expert testimony be based on scientifically valid methods with...
- Ecological Validity
- The degree to which a measurement or test procedure produces results that generalise from the controlled laboratory context to the real-world condition...
- Greely-Illes Critique (2007)
- Henry Greely and Judy Illes's 2007 analysis in the American Journal of Law and Medicine identifying five categories of problem with fMRI...
- No Lie MRI
- A San Diego-based company offering fMRI lie-detection services during the same period as Cephos. No court has admitted No Lie MRI evidence...
- US V. Semrau (2010/2012)
- The US district court Daubert hearing (2010) and Sixth Circuit affirmance (2012) excluding Cephos fMRI lie-detection evidence on grounds of insufficient testability,...