What Happens in a P300 EEG Lie Detector Test?

Initial Contact & Booking

Everything starts with a phone call or enquiry — to our team on 0161 524 5513 or via our contact form. This first conversation is completely confidential and costs nothing.

We will ask you to describe the situation in general terms — not to gather evidence, but to understand what kind of appointment you need and whether a P300 EEG test is the right approach for your situation. We will also begin to understand what specific concerns or allegations you want the test to address — this feeds directly into the stimulus design for the test itself.

We will then agree a time, date and location. Standard appointments are typically available within 24–48 hours. Same-day emergency appointments are available across most UK locations for an additional fee.

Preparation

There is very little you need to do — but a few simple steps help ensure the test data is as clean as possible.

• Sleep: Get a normal night's sleep — 7 to 8 hours ideally. Significant sleep deprivation can affect cognitive processing and potentially P300 latency.
• Alcohol: Avoid alcohol for 24 hours before your appointment. Alcohol affects neural signal quality.
• Hair: Wash your hair normally but do not use gel, wax, heavy conditioner or styling products on the morning of the test. These can insulate the scalp and reduce electrode contact quality.
• Medication: Continue any prescribed medications as normal. If you are taking sedatives or anything that significantly affects cognitive function, mention this when you book — not all medications affect P300 but some require consideration in test design.

The Morning of the Test

Eat normally — a light meal is fine, but avoid being hungry or having a very heavy meal immediately before the appointment. Either can affect concentration.

Caffeine is fine in your normal morning amount. Avoid significantly more caffeine than usual — not because it affects the P300 directly, but because it can increase general restlessness and movement during the test, which creates artefacts in the EEG signal.

Arrive a few minutes early if possible. There is no need to rush. Our locations are private, discreet and not shared with other businesses — you will not encounter anyone who knows why you are there.

Welcome & Settling In

You will be greeted by your examiner. The environment is private, calm and quiet — a meeting room or testing suite, not a clinical or institutional setting. You will be offered water and given a moment to settle before anything begins.

There is no pressure to start immediately. If you arrive feeling rushed or anxious, take the time you need. A calm start to the pre-test consultation produces better information for the test design — and our examiners are patient.

Pre-Test Consultation

This is the most important stage for ensuring the test produces a meaningful result. Your examiner will ask you — in detail and in complete confidence — about the specific situation you want the test to address.

For a relationship or infidelity case, this means identifying the specific details of the alleged situation — names, locations, dates, events — that form the basis of the suspicion. For a corporate investigation, it means identifying the specific knowledge that only someone involved in the alleged conduct would possess.

This information is used to design the probe stimulus set for the test. The quality of the stimulus design is the single most important factor in the accuracy of the result — so this conversation is taken seriously. If the specific details are vague or insufficient to design a reliable test, your examiner will tell you and discuss how to improve them before proceeding.

At the end of the consultation, the stimulus set is finalised and your examiner explains exactly what the test will involve — what you will see, what you will be asked to do, and what happens with the data.

Consent

Before any testing equipment is touched, the person being tested gives their full, informed consent in writing. This is non-negotiable — we do not test anyone who is not voluntarily agreeing to be tested, and any indication of pressure or coercion means the test does not proceed.

The consent form explains what the test measures, how the data will be used, who will see the results, and how long the data will be held. You are given time to read it properly and ask any questions before signing.

Headset Fitting & Calibration

The BrainBit 8-channel EEG headset is placed on the head. It looks and feels similar to a lightweight headband — there is no gel, no needles, and no discomfort. The dry electrodes make light contact with the scalp.

Once fitted, your examiner checks the signal quality on all 8 channels using the monitoring equipment. You will be asked to sit still for a moment while this is verified. If any channel is showing poor signal quality — due to electrode position or hair product — the headset is gently adjusted until all channels are clean.

Only once signal quality meets our minimum standard across all channels does the test proceed. If adequate signal quality cannot be achieved, the appointment is rescheduled rather than proceeding with compromised data.

The Test

This is where many people expect something dramatic — and where most people are surprised by how simple it actually is.

You sit facing a screen. Words, names or short phrases appear on the screen one at a time, each displayed for a fraction of a second. Your only active task is to press a button on a response pad when you see a specific category of item — for example, "press when you see a number." This task ensures you are attending to each stimulus as it appears.

You are not asked to speak. You are not asked any verbal questions. There are no wires attached to your body other than the headset. The EEG records your brain's electrical activity continuously and silently while the stimuli appear.

The probe stimuli — the specific items related to the matter being investigated — are embedded within the sequence of neutral fillers. You cannot tell which items are probes. Your examiner knows, but you do not. This blind presentation is essential for the integrity of the result.

You may feel bored. You may feel tired towards the end. You may notice that some items feel familiar. All of this is normal. The headset is recording what your brain does, not what you think you feel. Just keep pressing the button when you see the target category and let the test complete.

Data Processing

Once the stimulus sequence is complete, the headset is removed. You are welcome to use the waiting area, have a drink of water and take a break while the data is processed.

Your examiner works through the following steps with the raw EEG data:

• The continuous recording is segmented into time windows around each stimulus
• Artefact detection identifies and excludes epochs contaminated by movement or blinks
• Clean epochs are averaged separately for probe stimuli and neutral fillers
• P300 amplitude and latency are measured for each stimulus type across all channels
• A deception probability score is calculated using our validated statistical model
• The examiner reviews the output and confirms the result before communicating it

This typically takes 20 to 30 minutes. You will not be waiting in a silent room wondering — your examiner will keep you updated on progress.

Result Delivery

The result is communicated verbally, clearly and directly. Your examiner will tell you the outcome — clear (No Deception Indicated) or deception-indicated — and explain what it means in plain language. They will also explain the deception probability score and what confidence level underpins the result.

You can ask questions. You can ask for the explanation to be repeated. You can sit with it for a moment before saying anything. There is no rush.

If the result is clear, your examiner will confirm this and explain what the full written report will contain. If the result is inconclusive, your examiner will explain why — specifically, what aspect of the data fell below our minimum threshold — and discuss retest options. If deception is indicated, your examiner will explain the finding and signpost appropriate next steps and support.

The Written Report

The full written report arrives by secure email within 24 hours. It is formatted for both personal use and submission to HR, legal or insurance processes if required.

The report includes:

• Executive summary with the overall result in plain language
• The deception probability score with confidence interval
• Raw EEG waveform data for all 8 channels
• P300 amplitude and latency measurements per stimulus category
• Artefact rejection summary — how many epochs were excluded and why
• The examiner's professional conclusion signed with credentials
• Protocol documentation and test date, location and consent records

This report is yours. We hold a secure copy in line with our data retention policy — typically 12 months — and it is not shared with any third party without your explicit consent.