Skin conductance

A sample GSR signal of 60 seconds.

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 depending on the moisture of the skin, caused by sweat. Sweat being controlled by the sympathetic nervous system,^[1] so skin conductance is used as an indication of psychological or physiological arousal. Therefore, if the sympathetic branch of the autonomic nervous system is highly aroused, then sweat gland activity will also increase, which in turn increases skin conductance. In this way, skin conductance can be used as a measure of emotional and sympathetic responses.^[2] There has been a long history of electrodermal activity research, most of it dealing with spontaneous fluctuations or reactions to stimuli.

History

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.^[3] The controversial Austrian psychoanalyst Wilhelm Reich also studied GSR 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.'^[4] 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, some skin conductance monitoring devices, such as galvanometers, are still in use because they are inexpensive.

Description

Our extremities, including our fingers, palms, and soles of feet display different bio-electrical phenomena. A skin conductance meter is a device that measures the electrical conductance 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.

Physiological Basis

The combined changes between galvanic skin resistance and galvanic skin potential make up the galvanic skin response. Galvanic skin resistance (GSR) 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 in accordance with the emotional state of the subject. Galvanic skin potential (GSP) refers to the voltage measured between two electrodes without any externally applied current. This is measured by connecting the electrodes to a voltage amplifier. Similarly, this voltage varies with the emotional state of the subject.^[5]

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. These autonomic sympathetic changes alter sweating and blood flow, which in turn affects GSR and GSP.^[5]

Examples

A painful stimulus, such as a pinprick, will elicit a sympathetic response to the sweat glands, increasing secretion. Although this increase in sweat is generally very small, sweat contains water and electrolytes which increase electrical conductivity, thus lowering the electrical resistance of the skin. These changes will in turn affect the GSR.

Another common example is the vasodilation of blood vessels in the face, referred to as blushing, as well as increased sweating that occurs when one is embarrassed.^[5]

The SCR (skin conductance response) 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 responses are utilized as part of the polygraph or lie detector.

The SCR 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.^[6] This may indicate that the use of lie detectors relying on skin conductivity gives psychopaths an advantage in criminal investigations that non-psychopaths do not have.

Uses

SCR is used widely in psychological research due to its low cost and high utility.^[7] Oftentimes, the galvanic skin response is combined with the recording of heart rate, respiratory rate, and blood pressure because they are all autonomic dependent variables. Skin conductance 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 because the nervous system's control of heart rate, respiratory rate, blood pressure, and sweating are all autonomic meaning they cannot be consciously changed.^[5]

Many biofeedback therapy devices utilize skin conductance to measure and present an individual's stress response with the goal of helping the user to control their anxiety.^[8]

The E-meter, which is used by the Church of Scientology, is a skin conductance measurement device.^[9]

Skin conductance measurement is also becoming more popular in hypnotherapy and psychotherapy practices 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. ^{[citation needed]}

Possible Problems

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 when given the same stimulus level. Lastly, galvanic skin responses are delayed one-three seconds. Combined, these factors show the complexity of the relationship between the GSR and sympathetic activity.^[5]

See also

• Electroacupuncture
• Affective computing
• Biosignal

Notes

References

• Conesa, J. (1995). Electrodermal palmar asymmetry and nostril dominance. Perceptual and Motor Skills, 80, 211-216.
• Carlson, Neil (2013). Physiology of Behavior. New Jersey: Pearson Education, Inc. ISBN 978-0-205-23939-9.
• 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.
• Nagai, Y.; Goldstein, L. H.; Fenwick, P. B. C.; Trimble, M. R. (2004). "Clinical efficacy of galvanic skin response biofeedback training in reducing seizures in adult epilepsy: A preliminary randomized controlled study". Epilepsy & Behavior 5 (2): 216–223. doi:10.1016/j.yebeh.2003.12.003. PMID 15123023. 
• Loggia, M. L.; Juneau, M. N.; Bushnell, M. C. (2011). "Autonomic responses to heat pain: Heart rate, skin conductance, and their relation to verbal ratings and stimulus intensity". PAIN 152 (3): 592–598. doi:10.1016/j.pain.2010.11.032. PMID 21215519. 

External links

• 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