Polygraph Glossary Practice

event-related potentials

Definition

Event-related potentials (ERPs) are changes in the brain's electrical activity in response to a stimulus, recorded as voltage changes at the scalp. ERPs are extracted by averaging brain waves across multiple stimulus presentations. Several types exist (N100, N200, P300, N400), with the P300 showi...

What Are Event-Related Potentials?

Event-related potentials (ERPs) are stimulus-locked changes in brain electrical activity recorded via EEG. ERPs are extracted by averaging brain waves across many stimulus presentations, cancelling random background activity to reveal the consistent brain response. Several ERP components have been investigated for deception detection applications.

Key Components

The most studied component is the P300 — a positive deflection ~300ms after a stimulus the brain categorises as significant or rare. In a CIT paradigm, the P300 to a critical item is larger for guilty examinees who recognise it than for innocent ones. Other studied components include the ERN (conflict monitoring) and the N400 (semantic processing anomalies during deception).

Methodology

Individual ERP responses are tiny (microvolts) and buried in larger background EEG activity. The averaging technique requires 20–50+ stimulus repetitions, needing controlled presentations and relatively long sessions — a practical limitation versus standard polygraph testing which typically presents each question only 3–5 times across charts.

Current Status

ERP-based detection offers theoretical advantages: direct brain measurement, potential countermeasure resistance, and higher specificity in CIT applications. However, it remains primarily research-based, requires specialised equipment and expertise, and lacks the field validation supporting standard polygraph techniques. ERPs are a subset of the broader category of evoked cortical potentials.

Cross-references

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