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The Guilty Knowledge Test (GKT) (also known as the Concealed Information test (CIT) or as the peak of tension test) is used with polygraphs.


A series of words, sounds, or pictures are presented via computer to the subject for a fraction of a second each.

Each of these stimuli are organized by the test-giver to be a “Target,” “Irrelevant,” or a “Probe.” )The Target stimuli are chosen to be relevant information to the tested subject, and are used to establish a baseline brain response for information that is significant to the subject being tested.

The subject is instructed to press one button for Targets, and another button for all other stimuli.


Most of the non-Target stimuli are Irrelevant, and are totally unrelated to the situation that the subject is being tested for. The Irrelevant stimuli do not elicit a MERMER, and so establish a baseline brain response for information that is insignificant to the subject in this context.

Some of the non-Target stimuli are relevant to the situation that the subject is being tested for. These stimuli, or Probes, are relevant to the test, are significant to the subject, and will elicit a MERMER, signifying that the subject has responded to stimuli showing it to be significant. If a subject is lacking this information in their brain, the response to the Probe stimuli will be indistinguishable from the Irrelevant stimuli. This response does not elicit a MERMER, indicating that the information is absent from their mind. Note that there does not have to be an emotional response of any kind to the stimuli- this test is entirely reliant upon recognition response to the stimuli, and relies upon a difference in recognition.

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