Use of a device to measure and convey physiological information back to a subject. It has been proposed as a potential countermeasure approach. Biofeedback is not a countermeasure in itself, but rather a means of teaching a subject to influence autonomic responsivity. Research indicates that biofeedback is better suited for self-regulation of tonic activity than phasic activity. As a result, it may be useful to dampen or increase responsiveness in general during a test, but less so within a test to a given question. It has been suggested that this has implications for test formats such as Relevant/Irrelevant and Peak of Tension, but probably not for tests using comparison questions such as the Reid and Zone formats. Biofeedback can also be used to enhance responsiveness in subjects during testing. It has been hypothesized that the immediate biofeedback serves to elicit greater responding to questions when deception is practiced by the examinee. There is some empirical evidence of this effect, but it has not been unequivocally established.