Electrodermal activity (EDA), is the property of the human body that causes continuous variation in the electrical characteristics of the skin. Historically, EDA has also been known as skin conductance, galvanic skin response (GSR), electrodermal response (EDR), psychogalvanic reflex (PGR), skin conductance response (SCR), and skin conductance level (SCL). The long history of research into the active and passive electrical properties of the skin by a variety of disciplines has resulted in an excess of names, now standardized to electrodermal activity (EDA).
The traditional theory of EDA holds that skin resistance varies with the state of sweat glands in the skin. Sweating is controlled by the sympathetic nervous system, and skin conductance is an indication of psychological or physiological arousal. If the sympathetic branch of the autonomic nervous system is highly aroused, then sweat gland activity also increases, which in turn increases skin conductance. In this way, skin conductance can be a measure of emotional and sympathetic responses. More recent research and additional phenomena (resistance, potential, impedance, and admittance, sometimes responsive and sometimes apparently spontaneous) suggest this is not a complete answer, and research continues into the source and significance of EDA.
In 1849, Dubois-Reymond in Germany first observed that human skin was electrically active. His immersed the limbs of his subjects in a zinc sulfate solution and found that electrical current flowed between a limb with muscles contracted and one that was relaxed. He therefore attributed his EDA observations to muscular phenomena. Thirty years later, in 1878 in Switzerland, Hermann and Luchsinger demonstrated a connection between EDA and sweat glands. Hermann later demonstrated that the electrical effect was strongest in the palms of the hands, suggesting that sweat was an important factor.
Vigouroux (France, 1879), working with emotionally distressed patients, was the first researcher to relate EDA to psychological activity. In 1888, the French neurologist Féré demonstrated that skin resistance activity could be changed by emotional stimulation and that activity could be inhibited by drugs.
In 1889 in Russia, Ivane Tarkhnishvili observed variations in skin electrical potentials in the absence of any external stimuli, and he developed a meter to observe the variations as they happened in real time.
The scientific study of EDA began in the early 1900s. One of the first references to the use of EDA instruments in psychoanalysis is the book by C. G. Jung entitled Studies in Word Analysis, published in 1906. Jung and his colleagues used the meter to evaluate the emotional sensitivities of patients on lists of words during word association. Jung was so impressed with EDA monitoring, he allegedly cried, "Aha, a looking glass into the unconscious!" Jung and his colleagues used meters to evaluate the emotional sensitivities of patients Jung described his use of the device in counseling in his book, Studies in Word Association, and such use has continued with various practitioners.
The controversial Austrian psychoanalyst Wilhelm Reich also studied EDA in his experiments at the Psychological Institute at the University of Oslo in 1935 and 1936 to confirm the existence of a bio-electrical charge behind his concept of vegetative, pleasurable 'streamings.'
By 1972, more than 1500 articles on electrodermal activity had been published in professional publications, and today EDA is regarded as the most popular method for investigating human psychophysiological phenomena. As of 2013, EDA monitoring was still on the increase in clinical applications. The Church of Scientology uses a custom built EDA monitor in Dianetic and Scientology religious confessionals ("auditing") called an E-meter.
Human extremities, including fingers, palms, and soles of feet display different bio-electrical phenomena. They can be detected with an EDA meter, a device that displays the change electrical conductance between two points over time. 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.
The combined changes between electrodermal resistance and electrodermal potential make up electrodermal activity. Galvanic skin resistance (GSR) was an older term that refers to the recorded electrical resistance between two electrodes when a very weak current is steadily passed between them. The electrodes are normally placed about an inch apart, and the resistance recorded varies according to the emotional state of the subject. Galvanic skin potential (GSP) refers to the voltage measured between two electrodes without any externally applied current. It is measured by connecting the electrodes to a voltage amplifier. Similarly, this voltage varies with the emotional state of the subject.
Due to the response of the skin and muscle tissue to external and internal stimuli, the conductance can vary by several microsiemens, and a correctly calibrated device can display the subtle changes. There is a relationship between sympathetic activity and emotional arousal, although the electrical change alone does not identify which specific emotion is being elicited. These autonomic sympathetic changes alter sweat and blood flow, which in turn affects GSR and GSP.
A painful stimulus such as a pinprick elicits a sympathetic response by the sweat glands, increasing secretion. Although this increase is generally very small, sweat contains water and electrolytes which increase electrical conductivity, thus lowering the electrical resistance of the skin. These changes in turn affect the GSR. Another common example is the vasodilation (dilation) of blood vessels in the face, referred to as blushing, as well as increased sweating that occurs when one is embarrassed.
The EDA is highly responsive to emotions in some people. Fear, anger, startled response, orienting response and sexual feelings are among the reactions that may be reflected in EDA. These responses are utilized as part of the polygraph or lie detector.
The EDA 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 competitively unfair offers. This may indicate that the EDA aspect of a polygraph may be deceptive in a criminal investigation.
EDA is used widely in psychological research due to its low cost and high utility. Oftentimes, the galvanic skin responses are combined with the recording of heart rate, respiratory rate, and blood pressure because they are all autonomic dependent variables. EDA measurement is one component of polygraph devices and is used in scientific research of emotional or physiological arousal. Polygraphs are often used as lie detectors.
EDA measurement is also becoming more popular in hypnotherapy and psychotherapy practices for detecting depth of hypnotic trance prior to the commencement of suggestion therapy. 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.
External factors such as temperature and humidity affect GSR measurements, which can lead to inconsistent results. Internal factors such as medications can also change GSR measurements. Responses have demonstrated inconsistency even with the same stimulus level. Lastly, galvanic skin responses are delayed 1-3 seconds. Combined, these factors show the complexity of the relationship between the EDA and sympathetic activity. The skill of the operator may be a significant factor in the successful application of the tool.
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Electrodermal activity (EDA) is now the preferred term for changes in electrical conductance of the skin, including phasic changes that have been referred to as galvanic skin responses (GSR)
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By 1906 [Jung] was using GSR and breath measurement to note changes in respiration and skin resistance to emotionally charged worlds. Found that indicators cluster around stimulus words which indicate the nature of the subject's complexes...Much later L. Ron Hubbard used this approach in Scientology's "auditing," using the "e-meter" (a galvanic skin response indicator) to discern the presence of complexes.
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- University of Kuopio page on GSR Use
- Cornell GSR Class Project
- Instructions on making and using a GSR sensor
- GSR2: first portable unit, from 1976