Galvanic Skin Response (GSR) in Polygraph Testing

Defining GSR in Plain Language

Galvanic skin response (GSR) is a physiological phenomenon in which the electrical conductance of the skin changes in response to emotional arousal, stress, or cognitive effort. When you experience a sudden emotion — fear, excitement, anxiety, or the stress of attempting to deceive — your sympathetic nervous system activates eccrine sweat glands, particularly those concentrated in the palms of your hands and the soles of your feet Verified History of Polygraph
Confirms Keeler patented prototype of modern polygraph in 1939 and founded first polygraph school in 1948. This three-channel design became the standard configuration for polygraph testing for several decades. In 1939, Keeler patented what is now considered the prototype of the modern polygraph [16]Verified Study on accuracy of polygraph inspection and GSR evaluation
Verified that GSR channels occupy an important proportion in judging stimulus responses and validated palm electrode placement.

Keeler's addition of the GSR channel was debated among early practitioners. Some argued that skin conductance measurements were too variable to be reliable. Others, including John E. Reid, championed the channel as a powerful complement to cardiovascular and respiratory data. Over time, research increasingly supported the value of the electrodermal channel, and it became — and remains — an indispensable component of every professional polygraph system.

A Naming Confusion Resolved

One of the most common sources of confusion for consumers, students, and even some professionals is the overlapping terminology used to describe the same physiological phenomenon. As Wikipedia notes, EDA has historically "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)" [8]Verified Electrodermal activity — Wikipedia
Confirms historical timeline of EDA discovery, terminology standardization, and physiological mechanisms including sweat gland density.

Galvanic Skin Response (GSR) is the oldest and most widely recognized term, named after Luigi Galvani who pioneered the study of bioelectricity — though his connection to the terminology is largely an accident of history, as Galvani's cited work focused on electricity and muscular contractions rather than skin conductance [8]Verified Electrodermal activity — Wikipedia
Confirms historical timeline of EDA discovery, terminology standardization, and physiological mechanisms including sweat gland density. It is still commonly used in the polygraph industry and consumer contexts.

Electrodermal Activity (EDA) is the modern umbrella term preferred by the scientific community since the 1960s. EDA encompasses all electrical phenomena of the skin, including both tonic (baseline) and phasic (stimulus-specific) components. This is the term you will find in peer-reviewed research journals.

Skin Conductance Response (SCR) refers specifically to the rapid, phasic change in skin conductance triggered by a stimulus. In polygraph context, this is the "spike" that appears on the electrodermal channel when a significant question is asked. Skin Conductance Level (SCL) is the tonic or baseline level of skin conductance measured over longer periods. SCL changes slowly and reflects general arousal state rather than responses to specific questions [8]Verified Electrodermal activity — Wikipedia
Confirms historical timeline of EDA discovery, terminology standardization, and physiological mechanisms including sweat gland density.

Psychogalvanic Reflex (PGR) is an outdated term from the early 20th century. The term fell out of scientific favor because "reflex" implies a simple, automatic response, while the reality is more nuanced.

For the purposes of this guide, all of these terms describe the same fundamental measurement: changes in the skin's electrical properties caused by sympathetic nervous system activation of eccrine sweat glands.

Electrode Placement and Setup

During a standard polygraph examination, the examiner attaches two small metal electrodes — typically stainless steel or silver/silver chloride (Ag/AgCl) plates — to two fingers on the examinee's non-dominant hand. The most common configuration places electrodes on the distal phalanges (fingertips) of the index and ring fingers. Some examiners prefer the middle and ring fingers, and some systems use palmar placement with flat electrodes strapped to the palm.

A 2019 study by Lim and Lee verified that GSR channels occupy an important proportion in judging responses to stimuli, and demonstrated that palm placement can produce accurate stimulus responses in individuals with compromised finger conductance, expanding the practical applicability of EDA measurement in polygraph testing [17]Verified CPS Elite Polygraph Systems — Stoelting Company
Confirms Stoelting CPS Elite specifications including 360 samples per second EDA sampling rate.

The electrodes are held in place by Velcro finger bands or small clips. A very low-voltage electrical signal (imperceptible to the examinee) is passed between the two electrodes through the skin. The polygraph instrument measures how easily this current flows — the conductance — in real time.

What the Examinee Experiences

From the examinee's perspective, GSR measurement is completely painless and unnoticeable. The electrodes feel like small metal discs against the fingertips. There is no shock, no vibration, and no sensation whatsoever from the measurement. Many examinees are surprised to learn that this unobtrusive sensor is capturing one of the most diagnostically valuable channels in the entire polygraph system. If you want to know more about what happens during the full exam process, read our guide on finding a private lie detector test near you.

Preparation for your test typically includes instructions to avoid applying lotion, hand sanitizer, or other substances to the hands before the examination, as these can interfere with electrode contact and conductance measurements. You should also be aware that caffeine can affect polygraph test results.

Technical Specifications

Professional polygraph systems measure skin conductance with impressive precision. The measurement range is typically 0-100 microsiemens (µS), with most examinees falling between 2-20 µS at rest. Modern digital systems achieve resolution of 0.001 µS or better. Sampling rates vary by manufacturer and model — Stoelting's CPS Elite system samples EDA at 360 samples per second [18]Verified ParagonX Polygraph System — Limestone Technologies
Confirms ParagonX native 625 samples per second per channel and Ag/AgCl electrode options, while the Limestone Technologies ParagonX achieves a native 625 samples per second per channel, the highest sampling rate of any polygraph instrument [19]Verified ASTM E2439 Standard Guide for Instrumentation, Sensors and Operating Software Used in Forensic PDD Examinations
Confirms ASTM E2439 set minimum requirements for polygraph instrumentation including electrodermal measurement; designation E2439-09(2016), withdrawn 2025. Applied voltage is typically 0.5V DC, well below any perceptible threshold.

The ASTM E2439 standard — formally titled "Standard Guide for Instrumentation, Sensors and Operating Software Used in Forensic Psychophysiological Detection of Deception (Polygraph) Examinations" — set forth minimum requirements for polygraph instrumentation, specifying that instruments must simultaneously record respiratory, electrodermal, and cardiovascular activity as a minimum [20]Verified Habituation processes of skin conductance response and normalized pulse volume in pseudo concealed information test
Revealed differential habituation patterns between SCR and pulse volume measures in CIT paradigm. This standard (designation E2439-09, reapproved 2016) was withdrawn in 2025 [20]Verified Habituation processes of skin conductance response and normalized pulse volume in pseudo concealed information test
Revealed differential habituation patterns between SCR and pulse volume measures in CIT paradigm. For more on how modern sensors are built, see our guide on polygraph sensor technology.

Understanding the Two Components

The electrodermal signal recorded during a polygraph examination contains two distinct components. The tonic component (SCL) is the slowly changing baseline level of skin conductance. It reflects general arousal, environmental temperature, hydration, and overall anxiety level. It changes over minutes and provides context but is not directly used for question-by-question comparison [8]Verified Electrodermal activity — Wikipedia
Confirms historical timeline of EDA discovery, terminology standardization, and physiological mechanisms including sweat gland density.

The phasic component (SCR) is the rapid, stimulus-linked response that appears 1-3 seconds after a question. It reflects the autonomic response to a specific stimulus, lasts 2-10 seconds, and is what examiners primarily analyze when scoring the electrodermal channel. As scientists involved in basic research are interested in both electrodermal level and electrodermal responses, applied psychophysiology in polygraph evaluation involves primarily electrodermal responses [4]Verified Practical Polygraph: FAQ on Electrodermal Activity and the Electrodermal Sensor
Confirms EDA data has stronger correlation with external criterion compared to other channels in comparison question testing. Habituation research by Hamamoto et al. (2014) revealed differential habituation patterns between skin conductance and pulse volume measures, suggesting that strategic timing and weighting of different physiological channels could optimize detection accuracy [21]Verified Brute force comparison: A Monte Carlo study of OSS-3 and human polygraph scorers
Confirms OSS-3 demonstrated balanced sensitivity/specificity and is a free open-source cross-platform algorithm.

What Examiners Look For

When scoring the electrodermal activity channel, trained polygraph examiners evaluate several characteristics of the phasic response. The amplitude — the height or magnitude of the skin conductance response — is the primary scoring feature, often referred to as a "Kircher feature" [22]Verified The Polygraph and Lie Detection (Chapter 8: Conclusions and Recommendations)
Confirms NRC finding that polygraph tests can discriminate lying from truth at rates above chance, with accuracy index interquartile range of 0.81-0.91. Larger responses to relevant questions (compared to comparison questions) suggest greater emotional arousal during potentially deceptive answers.

Latency refers to the time between question onset and response peak. Normal latency is 1-3 seconds. Unusually fast or slow responses may indicate countermeasure use or other artifacts. Rise time measures how quickly the response reaches its peak; steeper rises generally indicate stronger sympathetic activation. Recovery time indicates how quickly conductance returns to baseline — slower recovery (longer half-recovery time) can indicate sustained arousal from a deceptive response.

These features are compared between relevant questions (about the issue under investigation) and comparison questions (designed to elicit a known emotional response from truthful subjects). The differential response pattern — not the absolute magnitude — is what matters for determining deception. For more on how salience drives these differential responses, see our article on salience in polygraph testing.

The Multi-Channel Approach to Lie Detection

A modern polygraph examination records at least four physiological channels simultaneously. Current polygraph machines typically record thoracic and abdominal respirations, a cardiovascular signal, and an electrodermal signal [3]Verified The Polygraph and Lie Detection (Appendix F: Computerized Scoring of Polygraph Data)
Confirms the electrodermal channel is considered 'the most diagnostic' by many polygraph researchers and documents CPS and PolyScore scoring algorithms. Understanding where GSR fits among these channels provides essential context.

Channel 1: Respiration (Pneumograph) — Two pneumograph tubes (thoracic and abdominal) measure breathing rate, depth, and pattern. Channel 2: Cardiovascular (Cardiosphygmograph) — A blood pressure cuff on the upper arm measures relative blood pressure changes, heart rate, and pulse amplitude. Channel 3: Electrodermal Activity (GSR) — Finger electrodes measure skin conductance changes driven by eccrine sweat gland activity. Often the most reactive channel to emotional stimuli and cognitively demanding deception. Channel 4: Motion / Activity Sensor — Seat pads, arm sensors, or movement detectors identify physical countermeasure attempts and excessive movement.

Some advanced systems also include a photoplethysmograph (PPG) on the fingertip, which measures blood volume pulse changes. To explore alternative and complementary technologies, read about neuroscience-based polygraph tests including fMRI, EEG, and NIRS, or learn about the EyeDetect test as an emerging alternative.

Why Multi-Channel Analysis Outperforms Single Channels

Research — including the National Research Council's 2003 report — has confirmed that in populations untrained in countermeasures, specific-incident polygraph tests can discriminate lying from truth telling at rates well above chance [23]Verified Meta-Analytic Survey of Criterion Accuracy of Validated Polygraph Techniques
Confirms APA meta-analysis finding 89% accuracy for single-issue tests, 85% for multi-issue, 87% overall across all validated techniques. The APA's 2011 meta-analysis, which examined 38 studies covering 3,723 examinations, found that event-specific (single issue) diagnostic testing produced an aggregated decision accuracy of 89% (confidence interval 83%–95%) with an inconclusive rate of 11% [24]Verified Effects of diazepam and methylphenidate on the electrodermal detection of guilty knowledge
Demonstrates that pharmacological agents can affect electrodermal detection of concealed information. Multi-issue techniques produced 85% accuracy (confidence interval 77%–93%), and the combination of all validated techniques produced 87% decision accuracy (confidence interval 80%–94%) [24]Verified Effects of diazepam and methylphenidate on the electrodermal detection of guilty knowledge
Demonstrates that pharmacological agents can affect electrodermal detection of concealed information.

Individuals differ in their autonomic response patterns: some people are "electrodermal responders" who show strong GSR changes but minimal cardiovascular reactions, while others are "cardiovascular responders" with the opposite pattern. Research using real criminal interrogations confirmed that physiological response patterns during real interrogations differed meaningfully from those predicted by laboratory research, underscoring the importance of multi-channel assessment [5]Verified Experimental Evaluation of Galvanic Skin Response and Blood Pressure Change Indices During Criminal Interrogation
Confirms physiological response patterns during real criminal interrogations differed meaningfully from laboratory predictions. By recording and analyzing all channels simultaneously, polygraph testing captures the full spectrum of autonomic nervous system activation. For strategies on optimizing this multi-channel approach, see our guide on minimizing false positives and negatives in polygraph testing.

Medical Conditions and Medications

Several medical conditions and medications can influence electrodermal responses, which is why qualified examiners conduct thorough pretest interviews to identify potential complicating factors. Anticholinergic medications — such as atropine, certain antihistamines, and some antidepressants — block acetylcholine at sweat gland nerve endings, potentially reducing GSR amplitude. Research by Iacono, Boisvenu, and Fleming (1984) investigated the effects of diazepam and methylphenidate on the electrodermal detection of guilty knowledge [25]Verified Limestone Technologies — subsidiary of Lafayette Instrument Company
Confirms Limestone Technologies is a subsidiary of Lafayette Instrument Company.

Beta-blockers, while primarily affecting cardiovascular responses, can indirectly reduce sympathetic activation and dampen GSR. Benzodiazepines (anti-anxiety medications) can reduce overall sympathetic nervous system activation. Hormonal changes — including those associated with menopause — can also influence baseline electrodermal activity and response patterns.

Environmental factors such as ambient temperature, humidity, and the examinee's hydration level also affect tonic skin conductance levels. This is why polygraph examinations are conducted in climate-controlled environments whenever possible.

Current Manufacturer Systems

Three major manufacturers dominate the professional polygraph market. Lafayette Instrument Company produces the LX series (LX6 and LX7) and through its subsidiary Limestone Technologies produces the ParagonX system [19]Verified ASTM E2439 Standard Guide for Instrumentation, Sensors and Operating Software Used in Forensic PDD Examinations
Confirms ASTM E2439 set minimum requirements for polygraph instrumentation including electrodermal measurement; designation E2439-09(2016), withdrawn 2025[26]Verified LXSoftware — Lafayette Instrument Company
Confirms LXSoftware is bundled with OSS-3 scoring algorithm and compatible with LX4000, LX5000, LX6, and LX7 systems. Lafayette's LXSoftware is bundled with the Objective Scoring System (OSS-3) scoring algorithm [27]Verified OSS-3 scoring algorithm development sample study
Confirms OSS-3 used brute-force methods on N=292 confirmed field cases, and documents Kircher features including electrodermal phasic response amplitude. The ParagonX features a native 625 samples per second per channel and nine sensor inputs with Lemo precision connectors [19]Verified ASTM E2439 Standard Guide for Instrumentation, Sensors and Operating Software Used in Forensic PDD Examinations
Confirms ASTM E2439 set minimum requirements for polygraph instrumentation including electrodermal measurement; designation E2439-09(2016), withdrawn 2025.

Stoelting Company, which has been manufacturing polygraph instruments since 1930, produces the CPS Elite Polygraph system — their fourth-generation computerized system [18]Verified ParagonX Polygraph System — Limestone Technologies
Confirms ParagonX native 625 samples per second per channel and Ag/AgCl electrode options. The Elite records both skin conductance and skin resistance at 360 samples per second, with CPS Fusion software for scoring and analysis [18]Verified ParagonX Polygraph System — Limestone Technologies
Confirms ParagonX native 625 samples per second per channel and Ag/AgCl electrode options.

All three manufacturers' systems include dedicated EDA sensor kits featuring gold-plated or Ag/AgCl electrodes designed for optimal conductance recording. For a technical deep dive into how the Lafayette OSS-3 algorithm works, see our companion article.

Computer-Assisted Scoring Systems

Modern polygraph scoring integrates computer algorithms that analyze electrodermal data alongside other channels. The OSS-3 (Objective Scoring System, version 3), developed by Raymond Nelson, Donald Krapohl, and Mark Handler, demonstrated balanced sensitivity and specificity and provided significant improvements over previous OSS versions [22]Verified The Polygraph and Lie Detection (Chapter 8: Conclusions and Recommendations)
Confirms NRC finding that polygraph tests can discriminate lying from truth at rates above chance, with accuracy index interquartile range of 0.81-0.91[28]Verified PolyScore — Johns Hopkins University Applied Physics Laboratory
Confirms PolyScore was developed by JHU-APL and uses linear logistic regression for deception detection. The OSS-3 is a free and open-source algorithm available to all manufacturers, field examiners, and researchers [28]Verified PolyScore — Johns Hopkins University Applied Physics Laboratory
Confirms PolyScore was developed by JHU-APL and uses linear logistic regression for deception detection.

PolyScore, developed by the Johns Hopkins University Applied Physics Laboratory (JHU-APL), uses linear logistic regression and Bayesian probability for deception detection [3]Verified The Polygraph and Lie Detection (Appendix F: Computerized Scoring of Polygraph Data)
Confirms the electrodermal channel is considered 'the most diagnostic' by many polygraph researchers and documents CPS and PolyScore scoring algorithms[29]Verified A review of the polygraph: history, methodology and current status
Confirms Nelson, Krapohl, and Handler (2008) developed the empirically based manual scoring system and CPS algorithm details. PolyScore is available with Lafayette and Axciton instruments. The Computerized Polygraph System (CPS) scoring algorithm, based on research by Kircher and Raskin (1988) at the University of Utah, uses standard multivariate linear discriminant function analysis utilizing skin conductance amplitude, cardiograph baseline increase, and combined respiration line-length as its three primary features [3]Verified The Polygraph and Lie Detection (Appendix F: Computerized Scoring of Polygraph Data)
Confirms the electrodermal channel is considered 'the most diagnostic' by many polygraph researchers and documents CPS and PolyScore scoring algorithms.

The Empirical Scoring System (ESS), also developed by Nelson, Krapohl, and Handler, is a manually applied evidence-based scoring system that showed inexperienced examiners could produce decision accuracy equivalent to that of experienced examiners [30]Verified Mental and physical countermeasures reduce the accuracy of polygraph tests
Confirms countermeasures enabled approximately 50% of subjects to defeat polygraph and were difficult to detect either instrumentally or through observation.

Can Examinees Beat the GSR Channel?

One of the most frequently asked questions about polygraph testing is whether examinees can deliberately manipulate their GSR responses to defeat the test. Research in this area provides an important, nuanced picture.

The NRC's 2003 report noted that there is evidence that mental countermeasure effects "operate particularly through the electrodermal channel" [23]Verified Meta-Analytic Survey of Criterion Accuracy of Validated Polygraph Techniques
Confirms APA meta-analysis finding 89% accuracy for single-issue tests, 85% for multi-issue, 87% overall across all validated techniques. A landmark 1994 study by Honts, Raskin, and Kircher examined countermeasures with 120 subjects recruited from the general community. They found that both mental countermeasures (counting backward by 7) and physical countermeasures (biting the tongue or pressing toes to the floor) enabled approximately 50% of trained subjects to defeat the polygraph test [31]Verified Human versus computerized evaluations of polygraph data in a laboratory setting
Confirms Kircher and Raskin developed discriminant function of electrodermal, cardiovascular, and respiration measures for computerized polygraph scoring. Importantly, the study found that the strongest countermeasure effects were observed in cardiovascular measures rather than electrodermal measures, and the countermeasures were difficult to detect either instrumentally or through observation [31]Verified Human versus computerized evaluations of polygraph data in a laboratory setting
Confirms Kircher and Raskin developed discriminant function of electrodermal, cardiovascular, and respiration measures for computerized polygraph scoring.

The NRC review observed that while early work by Honts, Raskin, and Kircher (1987) suggested countermeasures could be detected, later research by Honts and colleagues suggests that polygraph examiners have difficulty detecting countermeasures [23]Verified Meta-Analytic Survey of Criterion Accuracy of Validated Polygraph Techniques
Confirms APA meta-analysis finding 89% accuracy for single-issue tests, 85% for multi-issue, 87% overall across all validated techniques. Modern polygraph systems include dedicated motion and activity sensors specifically designed to help identify physical countermeasure attempts. The integration of multiple channels and algorithmic scoring provides additional layers of protection against manipulation.

What the Science Shows

Research on the diagnostic value of the electrodermal channel in polygraph testing spans over a century. Multiple studies have confirmed EDA's importance as a scoring feature.

A number of studies have shown that EDA data has a stronger correlation with the external criterion compared to other data recorded during comparison question testing [4]Verified Practical Polygraph: FAQ on Electrodermal Activity and the Electrodermal Sensor
Confirms EDA data has stronger correlation with external criterion compared to other channels in comparison question testing. Kircher and Raskin (1988) developed computer algorithms processing physiological reactions and evaluated them with mock crime data, using a discriminant function of electrodermal, cardiovascular, and respiration measures [32]Verified An experimental comparison of the Psychological Stress Evaluator and the galvanic skin response in detection of deception
Found GSR achieved.92 interrater reliability and exceeded chance-level accuracy while PSE performed at chance levels. The NRC's 2003 report specifically identified the electrodermal channel as considered "the most diagnostic" by many polygraph researchers [3]Verified The Polygraph and Lie Detection (Appendix F: Computerized Scoring of Polygraph Data)
Confirms the electrodermal channel is considered 'the most diagnostic' by many polygraph researchers and documents CPS and PolyScore scoring algorithms.

Horvath (1978) conducted a pivotal comparison study that found the galvanic skin response achieved.92 interrater reliability and exceeded chance-level accuracy, while the Psychological Stress Evaluator showed detection accuracy at only chance levels with interrater reliability of just.38 Verified A comprehensive meta-analysis of the comparison question polygraph test
Meta-analysis of 138 datasets found CQT can be accurate, experimental studies are generalizable, and no publication bias detected. This study powerfully demonstrated GSR's superiority as a physiological measure for deception detection.

Nelson, Krapohl, and Handler (2008) conducted a Monte Carlo study comparing the OSS-3 scoring algorithm with human polygraph scorers, demonstrating that combining electrodermal data with other channels in algorithmic scoring produced robust and consistent accuracy [28]Verified PolyScore — Johns Hopkins University Applied Physics Laboratory
Confirms PolyScore was developed by JHU-APL and uses linear logistic regression for deception detection. The APA's comprehensive 2011 meta-analysis found that properly validated multi-channel techniques produced overall decision accuracy of 87%, with single-issue tests reaching 89% [24]Verified Effects of diazepam and methylphenidate on the electrodermal detection of guilty knowledge
Demonstrates that pharmacological agents can affect electrodermal detection of concealed information. A comprehensive 2021 meta-analysis by Honts and colleagues, examining 138 datasets, found that the CQT can be accurate and that experimental studies are generalizable to field conditions.

For information on how the polygraph field has evolved in the 21st century, including post-9/11 federal expansion, see our article on polygraph in the 2000s.