blind stimulation test

What Is a Blind Stimulation Test?

A blind stimulation test is a variant of the stimulation test in which the examiner genuinely does not know which card, number, or item the examinee selected. Unlike a standard stim test — where the examiner may know the answer and demonstrate the result — in the blind format, the examiner must rely entirely on the physiological data to identify the selected item. This makes the demonstration more compelling to the examinee and eliminates any possibility that the examiner's knowledge might influence the presentation.

How It Works

In a typical blind stimulation test, the examinee selects an item (often a number from a range) in a way that prevents the examiner from observing the choice. The examinee then denies selecting each option while connected to the polygraph. The examiner analyses the physiological responses to identify which item produced the strongest electrodermal, respiratory, and cardiovascular responses, and announces their determination to the examinee.

Advantages over Known-Solution Format

The blind format offers several advantages. First, it provides a genuine demonstration of the polygraph's capability — the examiner truly is detecting concealed information from the physiological data alone. Second, it eliminates the possibility that the examiner's prior knowledge might unconsciously influence their behaviour during the stim test (through subtle changes in voice tone, pacing, or body language). Third, the demonstration is more psychologically impactful for the examinee because they know the examiner had no way of knowing the answer through any channel other than the physiological data.

Psychological Function

Like all stimulation tests, the blind stim test produces a deception exemplar and influences the examinee's psychological set for the subsequent diagnostic portion of the examination. A successful blind identification powerfully demonstrates to the examinee that their physiological responses to concealed information are detectable, reinforcing the fear of detection mechanism for deceptive examinees and the comparison question concern mechanism for truthful ones.

Risk of Incorrect Identification

The primary disadvantage of the blind format is the possibility that the examiner may fail to correctly identify the selected item. An incorrect identification could undermine the examinee's confidence in the polygraph, potentially reducing the psychological mechanisms that support accurate testing. For this reason, some examiners prefer the known-solution format for the stim test, or use a combination of blind and known-solution stim tests. The APA Standards of Practice address the use of stimulation tests and the considerations involved in selecting the appropriate format.