Skin conductance, also known as galvanic skin response (GSR), electrodermal response (EDR), psychogalvanic reflex (PGR), skin conductance response (SCR) or skin conductance level (SCL), is a method of measuring the electrical conductance of the skin, which varies with its moisture level. This is of interest because the sweat glands are controlled by the sympathetic nervous system,[1] so skin conductance is used as an indication of psychological or physiological arousal. There has been a long history of electrodermal activity research, most of it dealing with spontaneous fluctuations or reactions to stimuli.
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The device measures the electrical conductance (which is the inverse of the electrical resistance) between 2 points, and is essentially a type of ohmmeter. The two paths for current are along the surface of the skin and through the body. Active measuring involves sending a small amount of current through the body.
Due to the response of the skin and muscle tissue to external and internal stimuli, the conductance can vary by several microsiemens. When correctly calibrated, the device can measure these subtle differences. There is a relationship between sympathetic activity and emotional arousal, although one cannot identify which specific emotion is being elicited. The SCR is highly sensitive to emotions in some people. Fear, anger, startle response, orienting response and sexual feelings are all among the reactions which may produce similar skin conductance responses. These reactions are utilized as part of the polygraph or lie detector.
Skin conductance response in regular subjects differs when given fair and unfair offers, respectively. However, psychopaths have been shown to have no difference in skin conductance between fair and unfair offers. [2]. This may indicate that the use of lie detectors relying on skin conductivity gives psychopaths an advantage that non-psychopaths do not have in criminal investigations.
SCR is used widely in psychological research due to its cheap and effective nature [3]. It works by measuring the sympathetic nervous systems reaction to stimuli. This means the neurotrasmitter involved, unlike most ANS responses is acetylcholine, not epinephine. The device usually measures the sweat in the palm of the hand, or sole of foot.
The scientific study of GSR began in the early 1900s. One of the first references to the use of GSR instruments in Psychoanalysis is the book by C. G. Jung entitled Studies in Word Analysis, published in 1906.[4] Wilhelm Reich also studied GSR in his experiments at the Psychological Institute at the University of Oslo in 1935-6 to confirm the existence of a bio-electrical charge behind his concept of vegetative, pleasurable 'streamings.'[5] GSR was used for a variety of types of research in the 1960s through the late 1970s, with a decline in use as more sophisticated techniques (such as EEG and MRI) replaced it in many areas of psychological research. As of 2010, skin conductance monitoring equipment is still in use because it is inexpensive (e.g. a galvanometer).
Skin conductance measurement is one component of polygraph devices and is used in scientific research of emotional or physiological arousal.
The E-meter, which is used by the Church of Scientology, is a skin conductance measurement device.[6]
Skin conductance measurement is also becoming more popular in hypnotherapy and psychotherapy practice where it can be used as a method of detecting depth of hypnotic trance prior to suggestion therapy commencing. When traumatic material is experienced by the client (for example, during hypnoanalysis), immediate changes in sweat rate can indicate that the client is experiencing emotional arousal. It is also used in behavior therapy to measure physiological reactions such as fear.
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