Galvanic Skin Response
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Electrodermal activity (EDA) is the property of the human body that causes continuous variation in the electrical characteristics of the
skin Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate animal, with three main functions: protection, regulation, and sensation. Other cuticle, animal coverings, such as the arthropod exoskeleton, have diffe ...
. Historically, EDA has also been known as skin conductance, galvanic skin response (GSR), electrodermal response (EDR), psychogalvanic reflex (PGR), skin conductance response (SCR), sympathetic skin response (SSR) 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 gland Sweat glands, also known as sudoriferous or sudoriparous glands, , are small tubular structures of the skin that produce sweat. Sweat glands are a type of exocrine gland, which are glands that produce and secrete substances onto an epithelial sur ...
s in the skin. Sweating is controlled by the
sympathetic nervous system The sympathetic nervous system (SNS) is one of the three divisions of the autonomic nervous system The autonomic nervous system (ANS), formerly referred to as the vegetative nervous system, is a division of the peripheral nervous system that s ...

sympathetic nervous system
, and skin conductance is an indication of psychological or physiological
arousal Arousal is the physiology, physiological and psychology, psychological state of being awoken or of Five senses, sense organs stimulated to a point of perception. It involves activation of the ascending reticular activating system (ARAS) in the h ...

arousal
. If the sympathetic branch of the
autonomic nervous system The autonomic nervous system (ANS), formerly referred to as the vegetative nervous system, is a division of the peripheral nervous system that supplies viscera, internal organs, smooth muscle and glands. The autonomic nervous system is a control ...

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 Potential generally refers to a currently unrealized ability. The term is used in a wide variety of fields, from physics to the social sciences to indicate things that are in a state where they are able to change in ways ranging from the simple re ...

potential
, impedance, electrochemical skin conductance, and
admittance In electrical engineering, admittance is a measure of how easily a circuit or device will allow a current to flow. It is defined as the multiplicative inverse, reciprocal of Electrical impedance, impedance, analogous to how Electrical Conductan ...
, sometimes responsive and sometimes apparently spontaneous) suggest that EDA is more complex than it seems, and research continues into the source and significance of EDA.


History

In 1849,
Dubois-Reymond
Dubois-Reymond
in
Germany Germany,, officially the Federal Republic of Germany, is a country in Central Europe. It is the second most populous country in Europe after Russia, and the most populous member state of the European Union. Germany is situated between ...

Germany
first observed that human skin was electrically active. He immersed the limbs of his subjects in a
zinc sulfate Zinc sulfate is an inorganic compound. It is used as a dietary supplement to treat zinc deficiency and to prevent the condition in those at high risk. Side effects of excess supplementation may include abdominal pain, vomiting, headache, a ...

zinc sulfate
solution and found that electric 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 PsychoanalysisFrom Greek: + . is a set of theories and therapeutic techniques"What is psychoanalysis? Of course, one is supposed to answer that it is many things — a theory, a research method, a therapy, a body of knowledge. In what might ...

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 to lists of words during . Jung was so impressed with EDA monitoring, he allegedly cried, "Aha, a looking glass into the unconscious!" 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 Wilhelm Reich ( , ; 24 March 1897 – 3 November 1957) was an Austrian Doctor of Medicine, doctor of medicine and a psychoanalysis, psychoanalyst, along with being a member of the second generation of analysts after Sigmund Freud. The author ...

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.


Description

Skin conductance is not under conscious control. Instead, it is modulated autonomously by sympathetic activity which drives human behavior, cognitive and emotional states on a subconscious level. Skin conductance, therefore, offers direct insights into autonomous emotional regulation. 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 The electrical resistance of an object is a measure of its opposition to the flow of electric current. Its Multiplicative inverse, reciprocal quantity is , measuring the ease with which an electric current passes. Electrical resistance shares s ...
between two points over time. The two current paths are along the surface of the skin and through the body. Active measuring involves sending a small amount of current through the body. Some studies include the human skin's response to alternating current, including recently deceased bodies.


Physiological basis

There is a relationship between emotional arousal and sympathetic activity, 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 (Galvanic skin potential). The amount of sweat glands varies across the human body, being highest in hand and foot regions (200–600 sweat glands per cm2). The response of the skin and muscle tissue to external and internal stimuli can cause the conductance to vary by several microsiemens. A correctly calibrated device can record and display the subtle changes. The combined changes between electrodermal resistance and electrodermal potential make up electrodermal activity. Galvanic skin resistance (GSR) is 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. This voltage also varies with the emotional state of the subject.


Examples

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 GSR. Another common manifestation 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. 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 A polygraph, often incorrectly referred to as a lie detector test, is a device or procedure that measures and records several physiological indicators such as blood pressure, pulse, Respiration (physiology), respiration, and Electrodermal activi ...
or lie detector test. EDA in regular subjects differs according to feelings of being treated fairly or unfairly, but
psychopaths Psychopathy, sometimes considered synonymous with sociopathy, is characterized by persistent antisocial behavior, impaired empathy Empathy is the capacity to understand or feel what another person is experiencing from within their fram ...
have been shown to manifest no such differences. This indicates that the EDA record of a polygraph may be deceptive in a criminal investigation.


Different units of EDA

EDA reflects both slow varying ''tonic'' sympathetic activity and fast varying ''phasic'' sympathetic activity. Tonic activity can be expressed in units of electrodermal level (SCL), while phasic activity is expressed in units of electrodermal responses (EDR). Phasic changes (EDR) are short-lasting changes in EDA that appear as a response to a distinct stimulus. EDRs can also appear spontaneously without an observable external stimulus. These types of EDRs are referred to as "nonspecific EDR" (NS.EDR). The phasic SCR is useful when investigating multifaceted attentional processes. Tonic changes (EDL) are based on the phasic parameters. The spontaneous fluctuations of nonspecific EDR can be used to evaluate tonic EDA. More specifically by using the frequency of "nonspecific EDR" as an index of EDA during a specific time period, e. g. 30–60 seconds. Tonic EDA is considered useful in investigations of general arousal and alertness.


Uses

EDA is a common measure of autonomic nervous system activity, with a long history of being used in psychological research. Hugo D. Critchley, Chair of Psychiatry at the
Brighton and Sussex Medical School Brighton and Sussex Medical School (BSMS) is a medical school formed as a partnership of the University of Brighton and the University of Sussex. Like other UK medical schools it is based on the principles and standards of 'Tomorrow's Doctors', ...
states, "EDA is a sensitive psychophysiological index of changes in autonomic sympathetic arousal that are integrated with emotional and cognitive states." Many
biofeedback Biofeedback is the process of gaining greater awareness of many physiology, physiological functions of one's own body by using Electronics, electronic or other instruments, and with a goal of being able to Manipulation (psychology), manipulate t ...

biofeedback
therapy devices utilize EDA as an indicator of the user's stress response with the goal of helping the user to control anxiety. EDA is used to assess an individual's neurological status without using traditional, but uncomfortable and expensive, EEG-based monitoring. It has also been used as a proxy of psychological stress. EDA has also been studied as a method of pain assessment in premature born infants. Often, EDA monitoring is combined with the recording of heart rate, respiratory rate, and blood pressure, because they are all autonomically dependent variables. EDA measurement is one component of modern polygraph devices, which are often used as lie detectors. The
E-meter The E-meter, originally the electropsychometer, is an electronic device for displaying the electrodermal activity (EDA) of a human being. It is used for auditing (Scientology), auditing in Scientology and divergent groups. The efficacy and legit ...
used by the
Church of Scientology The Church of Scientology is a group of interconnected corporate entities and other organizations devoted to the practice, administration and dissemination of Scientology, which is variously defined as a cult, a scientology as a business, bu ...
as part of its practice of "
auditing An audit is an "independent examination of financial information of any entity, whether profit oriented or not, irrespective of its size or legal form when such an examination is conducted with a view to express an opinion thereon.” Auditing ...
" and " security checking", is a custom EDA measurement device.


Possible problems

External factors such as temperature and humidity affect EDA measurements, which can lead to inconsistent results. Internal factors such as medications and hydration can also change EDA measurements, demonstrating inconsistency with the same stimulus level. Also, the classic understanding has treated EDA as if it represented one homogeneous change in arousal across the body, but in fact different locations of its measurement can lead to different responses; for example, the responses on the left and right wrists are driven by different regions of the brain, providing multiple sources of arousal; thus, the EDA measured in different places on the body varies not only with different sweat gland density but also with different underlying sources of arousal. Lastly, electrodermal responses are delayed 1–3 seconds. These show the complexity of determining the relationship between EDA and sympathetic activity. The skill of the operator may be a significant factor in the successful application of the tool.


See also

* Affective computing *
Biosignal A biosignal is any signal (electrical engineering), signal in living beings that can be continually Measuring instrument, measured and Monitoring (medicine), monitored. The term biosignal is often used to refer to bioelectrical signals, but it may ...
* Electroacupuncture


Notes


References

* *Carlson, Neil (2013). Physiology of Behavior. New Jersey: Pearson Education, Inc. . *Figner, B., & Murphy, R. O. (2010). Using skin conductance in judgment and decision making research. A Handbook of Process Tracing Methods for Decision Research: A Critical Review and User's Guide, 163–84.
Pflanzer, Richard. "Galvanic Skin Response and the Polygraph". BIOPAC Systems, Inc. Retrieved 5 May 2013
* * {{DEFAULTSORT:Skin Conductance Measuring instruments Electronic test equipment Skin physiology Forensic techniques