Psychogalvanometer & Polygraph History: GSR Origins 1888–1940

Carl Ludwig and the Foundation of Physiological Recording

The story of the psychogalvanometer — and by extension, the electrodermal activity channel in every modern polygraph — begins with a German physician's ambition to record the body's hidden processes. Carl Ludwig (1816–1895), a professor of physiology who worked at institutions across Germany, is widely considered one of the founders of modern experimental physiology. His development of the kymograph in 1847 — a rotating drum that recorded physiological changes on smoked paper — gave science its first reliable method for capturing biological signals over time.

Ludwig's laboratory at the University of Leipzig became a training ground for an entire generation of physiologists, many of whom would go on to pioneer electrodermal research. His insistence on precise measurement and graphical recording established the methodological framework that later researchers would apply specifically to skin electrical phenomena.

The late nineteenth century was a period of explosive growth in electrophysiology. In 1849, Dubois-Reymond in Germany first observed that human skin was electrically active [1]Verified Electrodermal Activity
Confirms EDA history from Dubois-Reymond's 1849 observation, terminology standardisation, role of sympathetic nervous system, and that by 1972 over 1,500 articles had been published. By the 1870s and 1880s, researchers across Europe were using increasingly sensitive galvanometers to detect tiny electrical changes in muscles, nerves, and eventually skin. By 1972, more than 1,500 articles on electrodermal activity had been published in professional publications [1]Verified Electrodermal Activity
Confirms EDA history from Dubois-Reymond's 1849 observation, terminology standardisation, role of sympathetic nervous system, and that by 1972 over 1,500 articles had been published. It was in this intellectual environment that the first observations of electrodermal activity were made — discoveries that would ultimately shape every modern polygraph examination.

The Galvanometer: The Instrument That Made Discovery Possible

Understanding the psychogalvanometer requires understanding the galvanometer itself — the instrument from which it takes its name. A galvanometer is a device that detects and measures small electrical currents by using the electromagnetic effect of a current flowing through a coil in a magnetic field. The deflection of a needle or mirror indicates the magnitude and direction of the current [2]Verified The History Corner: The Galvanometer
Confirms galvanometer's role in psychological research and history of EDA measurement.

By the 1880s, galvanometers had become sensitive enough to detect the extremely small electrical changes that occur at the surface of human skin. When researchers attached electrodes to a subject's palms or fingertips and connected them to a galvanometer circuit, they could observe the needle deflecting in response to various stimuli — sounds, images, pain, emotional triggers. The instrument that measured these psychologically-induced galvanic changes became known as a psychogalvanometer.

For the first time, researchers had an objective, external way to observe internal psychological states. The subject could not voluntarily control the galvanometer's needle. Skin conductance is not under conscious control — it is modulated autonomously by sympathetic activity which drives human behaviour, cognitive and emotional states on a subconscious level [1]Verified Electrodermal Activity
Confirms EDA history from Dubois-Reymond's 1849 observation, terminology standardisation, role of sympathetic nervous system, and that by 1972 over 1,500 articles had been published. This principle — the involuntary physiological betrayal of internal states — would become the conceptual foundation of polygraph testing. Learn more about how this principle operates in modern practice in our guide to galvanic skin response in polygraph testing.

Charles Féré and the Exosomatic Method (1888)

The first systematic scientific study of electrodermal activity is generally credited to Charles Féré (1852–1907), a French physician and neurologist who worked at the Bicêtre Hospital in Paris. In 1888, Féré published his observations that the electrical resistance of the skin decreased when subjects were presented with various sensory and emotional stimuli [3]Verified Note on Changes in Electrical Resistance Under the Effect of Sensory Stimulation and Emotion (Féré, 1888)
Confirms Féré's 1888 discovery as the first systematic study of electrodermal activity and founding of the exosomatic method. His experimental method involved passing a small external electrical current through the subject's skin and measuring changes in resistance using a galvanometer.

Féré's approach — now known as the exosomatic method because it applies an external source of current to the body — measures what we now call skin conductance response (SCR). When sweat gland activity increases, the skin becomes a better conductor of electricity, so resistance drops and conductance rises [1]Verified Electrodermal Activity
Confirms EDA history from Dubois-Reymond's 1849 observation, terminology standardisation, role of sympathetic nervous system, and that by 1972 over 1,500 articles had been published. Féré documented that this happened in response to visual stimuli, sounds, pain, and various emotional states.

What made Féré's work groundbreaking was its demonstration of a reliable, measurable physiological correlate of psychological arousal. Previous attempts to connect mind and body had relied on subjective reports or gross observations like blushing or trembling. Féré showed that a sensitive instrument could detect changes invisible to the naked eye — changes happening at the level of sweat gland activity driven by the autonomic nervous system. The exosomatic method he developed is the same basic principle used in the EDA channel of every modern polygraph instrument. When an examiner today attaches finger plates or electrodes to a subject's hand and measures skin conductance changes during a polygraph examination, they are using a direct descendant of Féré's 1888 technique.

Ivan Tarchanoff and the Endosomatic Method (1890)

Just two years after Féré's publication, the Russian physiologist Ivan Romanovich Tarchanoff (1846–1908) independently reported a different approach to measuring electrodermal phenomena. Working at the University of St. Petersburg, Tarchanoff discovered that the skin itself generates electrical potentials that change in response to stimulation — without the need for any external current [4]Verified A History of Lie Detection (Parts I & II)
Definitive two-part history of lie detection documenting Tarchanoff's endosomatic method, Jung's experiments, Benussi's respiratory work, and early American deception research. His method, now known as the endosomatic method, measures the skin's own internally generated electrical activity.

Tarchanoff's observation was that when a subject experienced emotional arousal, the electrical potential difference between two points on the skin's surface would change measurably. This phenomenon — sometimes called the Tarchanoff response or skin potential response (SPR) — represents a different aspect of the same underlying physiological process that Féré had measured.

Both methods detect activity driven by the eccrine sweat glands, which are controlled by the sympathetic branch of the autonomic nervous system [1]Verified Electrodermal Activity
Confirms EDA history from Dubois-Reymond's 1849 observation, terminology standardisation, role of sympathetic nervous system, and that by 1972 over 1,500 articles had been published. When the sympathetic nervous system is activated — whether by stress, anxiety, emotional arousal, or the cognitive effort of deception — the eccrine sweat glands increase their activity, changing the electrical properties of the skin. This is the fundamental mechanism that makes electrodermal measurement so valuable for polygraph testing. Understanding these factors that affect lie detector test results remains essential for modern examiners.

Otto Veraguth's Naming Convention

Swiss neurologist Otto Veraguth (13 May 1870 – 17 December 1944) made his primary contribution to the field through something critically important in science: standardised terminology [5]Verified Otto Veraguth
Confirms Veraguth's life dates (1870–1944), his work in Zurich, coining the term psychogalvanic reflex, and publication of Das psychogalvanische Reflexphänomen in 1909. Born in Chur, Switzerland, Veraguth studied medicine at the University of Zurich, where he trained under the influential neurologist Constantin von Monakow [5]Verified Otto Veraguth
Confirms Veraguth's life dates (1870–1944), his work in Zurich, coining the term psychogalvanic reflex, and publication of Das psychogalvanische Reflexphänomen in 1909. In 1900 he obtained his habilitation for neurology, and in 1918 was appointed associate professor of physical therapy at the University of Zurich [5]Verified Otto Veraguth
Confirms Veraguth's life dates (1870–1944), his work in Zurich, coining the term psychogalvanic reflex, and publication of Das psychogalvanische Reflexphänomen in 1909.

In the 1900s, Veraguth published a study of a phenomenon he called the 'psychogalvanic reflex' (psychogalvanischer Reflex), associated with observed changes in the electrical properties of the skin [5]Verified Otto Veraguth
Confirms Veraguth's life dates (1870–1944), his work in Zurich, coining the term psychogalvanic reflex, and publication of Das psychogalvanische Reflexphänomen in 1909. He first presented research on this phenomenon at the Second Congress for Experimental Psychology in Würzburg in 1906, with further publications in 1907 [6]Verified Das psychogalvanische Reflexphänomen — Veraguth 1906 Congress Presentation
Confirms Veraguth's 1906 Würzburg presentation on the psychogalvanic reflex and subsequent 1907 publications, and Benussi's 1913 research. This naming was significant for several reasons. First, it explicitly connected the galvanic (electrical) changes in the skin to their psychological origin. Second, by calling it a 'reflex,' Veraguth placed the phenomenon within the framework of involuntary neurological responses — something that happens automatically, below conscious control.

Veraguth published his comprehensive findings in his 1909 work Das psychogalvanische Reflexphänomen, published in Berlin by S. Karger [5]Verified Otto Veraguth
Confirms Veraguth's life dates (1870–1944), his work in Zurich, coining the term psychogalvanic reflex, and publication of Das psychogalvanische Reflexphänomen in 1909[7]Verified Das psychogalvanische Reflexphänomen
Confirms the full publication details of Veraguth's 1909 book published by S. Karger in Berlin. The work provided a thorough review of the phenomenon and its clinical applications. He demonstrated that the psychogalvanic reflex could be elicited by a wide range of stimuli, and that emotional stimuli caused greater deflections on a galvanometer connected to the skin via electrodes than did neutral stimuli [5]Verified Otto Veraguth
Confirms Veraguth's life dates (1870–1944), his work in Zurich, coining the term psychogalvanic reflex, and publication of Das psychogalvanische Reflexphänomen in 1909. He also noted significant individual differences in electrodermal reactivity, an observation that would later become important for polygraph baseline testing.

Veraguth's Influence on Clinical Practice

Beyond naming, Veraguth contributed to establishing standardised procedures for electrodermal measurement. He specified electrode placement, described the typical waveform of the psychogalvanic response, and discussed factors that could affect measurement reliability — skin temperature, moisture, electrode pressure, and the subject's baseline physiological state. Many of these practical considerations remain directly relevant to modern polygraph practice.

Veraguth also explored clinical applications of the psychogalvanic reflex in neurological diagnosis. He proposed that abnormal electrodermal responses could indicate neurological damage or dysfunction. From 1922 to 1924 he served as president of the Swiss Neurological Society [5]Verified Otto Veraguth
Confirms Veraguth's life dates (1870–1944), his work in Zurich, coining the term psychogalvanic reflex, and publication of Das psychogalvanische Reflexphänomen in 1909. His legacy is honoured by the SNG's Veraguth Medal for honorary presidents [8]Verified History of the Swiss Neurological Society
Confirms Veraguth was SNS president 1922–1924 and details of his career at the Institute for Brain Anatomy in Zurich. This clinical dimension of electrodermal measurement existed parallel to, and sometimes intersected with, the developing field of lie detection. Modern examiners should be aware of the considerations Veraguth raised, as discussed in our guide to factors affecting polygraph results.

The Zurich Connection

Perhaps the most famous early application of the psychogalvanometer came from Carl Gustav Jung (1875–1961), the Swiss psychiatrist who would become one of the most influential psychologists of the twentieth century. Working at the Burghölzli Psychiatric Clinic in Zurich — not far from where Veraguth was conducting his research — Jung incorporated the psychogalvanometer into his word association experiments beginning around 1906–1907 [4]Verified A History of Lie Detection (Parts I & II)
Definitive two-part history of lie detection documenting Tarchanoff's endosomatic method, Jung's experiments, Benussi's respiratory work, and early American deception research.

Jung's word association test presented subjects with a list of stimulus words, one at a time. The subject was instructed to respond as quickly as possible with the first word that came to mind. Jung measured two things: reaction time (how long it took to respond) and the psychogalvanic response (the change in skin conductance during and after each word). His hypothesis was that words touching on unconscious emotional conflicts — what he called 'complexes' — would produce both delayed reaction times and heightened galvanic skin responses.

The results were striking. When subjects encountered words related to their personal emotional conflicts, the psychogalvanometer showed clear, measurable spikes in skin conductance. These physiological responses occurred even when subjects showed no outward signs of distress and even when they were unaware of the significance of the triggering word. Jung had demonstrated that the psychogalvanometer could detect hidden psychological states. Peterson and Jung published their psycho-physical investigations with the galvanometer and plethysmograph in the journal Brain in 1907 [4]Verified A History of Lie Detection (Parts I & II)
Definitive two-part history of lie detection documenting Tarchanoff's endosomatic method, Jung's experiments, Benussi's respiratory work, and early American deception research.

From Complexes to Deception

For the history of lie detection, Jung's work was pivotal. He effectively proved the core principle that would underlie all future polygraph testing: that psychologically significant stimuli produce involuntary, measurable physiological responses, and that an instrument can detect what a person's conscious behaviour conceals.

It is important to note that Jung himself was not primarily interested in detecting lies. His focus was therapeutic — he wanted to identify and treat unconscious psychological conflicts. However, other researchers quickly recognised the deception-detection implications of his findings. If a psychogalvanometer could detect emotional responses to personally significant words, it could potentially detect the emotional responses associated with guilty knowledge or the act of lying.

This conceptual leap — from detecting unconscious complexes to detecting deliberate deception — was one of the most consequential developments in the early history of lie detection. It connected the psychogalvanometer to the work of researchers like Max Wertheimer, who had independently proposed using reaction time measures for crime detection, and laid the groundwork for the eventual integration of GSR measurement into polygraph instruments [9]Verified A Review of the Polygraph: History, Methodology and Current Status
Comprehensive review confirming Keeler added GSR channel in 1938 based on Summers' work, and confirming polygraph development from Marston through Larson to Keeler[10]Verified Lie Detection: Its History, Methods and Techniques
Early comprehensive account of lie detection history documenting the transition from ancient ordeals to scientific instruments. This same principle underpins the stim test procedure used by modern polygraph examiners.

Vittorio Benussi and the Respiratory Ratio

While the psychogalvanometer was being developed for clinical and experimental use, other researchers were exploring different physiological channels for detecting deception. The Italian psychologist Vittorio Benussi presented a paper before the Italian Society for Psychology in Rome in 1913, demonstrating that changes in the inspiration-to-expiration ratio occurred systematically when subjects were lying [6]Verified Das psychogalvanische Reflexphänomen — Veraguth 1906 Congress Presentation
Confirms Veraguth's 1906 Würzburg presentation on the psychogalvanic reflex and subsequent 1907 publications, and Benussi's 1913 research. Although Benussi's primary focus was respiration rather than electrodermal activity, his work established the broader principle of multi-channel physiological measurement that would eventually include the psychogalvanometer.

Benussi's research was significant because it demonstrated with scientific rigour that deception produces specific, measurable physiological patterns — not just vague arousal but patterned changes in specific physiological systems. This finding encouraged other researchers to investigate whether additional physiological channels, including GSR, could enhance deception detection accuracy when used in combination.

William Marston and the Systolic Blood Pressure Test

In the United States, the most prominent early deception researcher was William Moulton Marston, a Harvard-trained psychologist who developed the systolic blood pressure deception test beginning around 1913–1915 [9]Verified A Review of the Polygraph: History, Methodology and Current Status
Comprehensive review confirming Keeler added GSR channel in 1938 based on Summers' work, and confirming polygraph development from Marston through Larson to Keeler. Marston's approach was innovative but limited by its reliance on a single physiological measure.

Marston was aware of the psychogalvanometer research coming out of Europe, but his own instrument was focused exclusively on cardiovascular measures. Interestingly, Marston reportedly tested the potential of EDA in deception tests for the Army in 1917, but was unimpressed by the results at the time [11]Verified Credibility Assessment: Scientific Research and Applications (EDA in Polygraph)
Confirms EDA was slow to be adapted to polygraph, Marston's 1917 EDA tests, Summers' advocacy, and Veraguth's observations on habituation. The eventual recognition that combining multiple physiological channels — blood pressure, respiration, and galvanic skin response — would produce more reliable results than any single channel was one of the key insights that drove the development of the true polygraph (literally, 'many writings') instrument.

Harold Burtt and Early American Deception Research

Harold E. Burtt (1890–1991) at Ohio State University was another important early American figure who bridged psychology and law [12]Verified Through a Lens Brightly: A Glimpse into the History of Law-Psychology through its Textbooks
Confirms Harold Burtt (1890–1991) at Ohio State University as a neglected founder of psychology and law and author of the 1931 Legal Psychology textbook. Burtt served as department chair at Ohio State and authored Legal Psychology in 1931, one of the first evidence-based textbooks on the intersection of psychology and the legal system [12]Verified Through a Lens Brightly: A Glimpse into the History of Law-Psychology through its Textbooks
Confirms Harold Burtt (1890–1991) at Ohio State University as a neglected founder of psychology and law and author of the 1931 Legal Psychology textbook. His work covered deception detection among other forensic topics, and he has been called a 'neglected founder of psychology and law' [12]Verified Through a Lens Brightly: A Glimpse into the History of Law-Psychology through its Textbooks
Confirms Harold Burtt (1890–1991) at Ohio State University as a neglected founder of psychology and law and author of the 1931 Legal Psychology textbook. The existence of researchers like Burtt working on deception detection across multiple American universities demonstrates how rapidly the field was developing in the early twentieth century.

John Larson's Multi-Channel Innovation

The person who first implemented a continuous, multi-channel approach to deception detection was John Augustus Larson, a medical student and police officer working in Berkeley, California under the supervision of Police Chief August Vollmer. In 1921, Larson built an instrument that simultaneously recorded blood pressure, pulse, and respiration during questioning — the first device that could accurately be called a 'polygraph' in the modern sense [9]Verified A Review of the Polygraph: History, Methodology and Current Status
Comprehensive review confirming Keeler added GSR channel in 1938 based on Summers' work, and confirming polygraph development from Marston through Larson to Keeler[10]Verified Lie Detection: Its History, Methods and Techniques
Early comprehensive account of lie detection history documenting the transition from ancient ordeals to scientific instruments.

Notably, Larson's original 1921 instrument did not include a GSR channel. It recorded cardiovascular and respiratory changes but not electrodermal activity [11]Verified Credibility Assessment: Scientific Research and Applications (EDA in Polygraph)
Confirms EDA was slow to be adapted to polygraph, Marston's 1917 EDA tests, Summers' advocacy, and Veraguth's observations on habituation. The psychogalvanometer and the early polygraph existed as parallel traditions through the 1920s and early 1930s, each measuring different aspects of the body's response to psychological stimuli, each with its own strengths and limitations.

Key Milestones in Electrodermal and Polygraph History

1849 — Dubois-Reymond first observes that human skin is electrically active [1]Verified Electrodermal Activity
Confirms EDA history from Dubois-Reymond's 1849 observation, terminology standardisation, role of sympathetic nervous system, and that by 1972 over 1,500 articles had been published.

1888 — Charles Féré publishes his discovery of the exosomatic method, measuring skin resistance changes in response to stimuli [3]Verified Note on Changes in Electrical Resistance Under the Effect of Sensory Stimulation and Emotion (Féré, 1888)
Confirms Féré's 1888 discovery as the first systematic study of electrodermal activity and founding of the exosomatic method.

1890 — Ivan Tarchanoff independently reports the endosomatic method, detecting the skin's own electrical potential changes [4]Verified A History of Lie Detection (Parts I & II)
Definitive two-part history of lie detection documenting Tarchanoff's endosomatic method, Jung's experiments, Benussi's respiratory work, and early American deception research.

1906 — Otto Veraguth presents his work on the psychogalvanic reflex at the Second Congress for Experimental Psychology in Würzburg [6]Verified Das psychogalvanische Reflexphänomen — Veraguth 1906 Congress Presentation
Confirms Veraguth's 1906 Würzburg presentation on the psychogalvanic reflex and subsequent 1907 publications, and Benussi's 1913 research.

1906–1907 — Carl Jung incorporates the psychogalvanometer into word association experiments at the Burghölzli Clinic in Zurich [4]Verified A History of Lie Detection (Parts I & II)
Definitive two-part history of lie detection documenting Tarchanoff's endosomatic method, Jung's experiments, Benussi's respiratory work, and early American deception research.

1907 — Peterson and Jung publish their psycho-physical investigations with the galvanometer in the journal Brain [4]Verified A History of Lie Detection (Parts I & II)
Definitive two-part history of lie detection documenting Tarchanoff's endosomatic method, Jung's experiments, Benussi's respiratory work, and early American deception research.

1909 — Veraguth publishes Das psychogalvanische Reflexphänomen in Berlin [5]Verified Otto Veraguth
Confirms Veraguth's life dates (1870–1944), his work in Zurich, coining the term psychogalvanic reflex, and publication of Das psychogalvanische Reflexphänomen in 1909[7]Verified Das psychogalvanische Reflexphänomen
Confirms the full publication details of Veraguth's 1909 book published by S. Karger in Berlin.

1913 — Vittorio Benussi demonstrates respiratory changes during deception in Rome [6]Verified Das psychogalvanische Reflexphänomen — Veraguth 1906 Congress Presentation
Confirms Veraguth's 1906 Würzburg presentation on the psychogalvanic reflex and subsequent 1907 publications, and Benussi's 1913 research.

1913–1915 — William Marston develops the systolic blood pressure deception test [9]Verified A Review of the Polygraph: History, Methodology and Current Status
Comprehensive review confirming Keeler added GSR channel in 1938 based on Summers' work, and confirming polygraph development from Marston through Larson to Keeler.

1921 — John Larson builds the first continuous multi-channel polygraph in Berkeley, California (without GSR) [9]Verified A Review of the Polygraph: History, Methodology and Current Status
Comprehensive review confirming Keeler added GSR channel in 1938 based on Summers' work, and confirming polygraph development from Marston through Larson to Keeler[10]Verified Lie Detection: Its History, Methods and Techniques
Early comprehensive account of lie detection history documenting the transition from ancient ordeals to scientific instruments.

1929 — The Scientific Crime Detection Laboratory (SCDL) is established at Northwestern University in Chicago [13]Verified Teaching Forensic Science to the American Police and Public: The SCDL, 1929-1938
Confirms Northwestern University's Scientific Crime Detection Laboratory was established in 1929, Keeler headed polygraph department, and Inbau became director in 1938.

1930 — Leonarde Keeler moves to Chicago to work at the SCDL [13]Verified Teaching Forensic Science to the American Police and Public: The SCDL, 1929-1938
Confirms Northwestern University's Scientific Crime Detection Laboratory was established in 1929, Keeler headed polygraph department, and Inbau became director in 1938.

1936 — Father Walter G. Summers at Fordham University develops a specialised psychogalvanometer for criminal investigations [9]Verified A Review of the Polygraph: History, Methodology and Current Status
Comprehensive review confirming Keeler added GSR channel in 1938 based on Summers' work, and confirming polygraph development from Marston through Larson to Keeler.

1938 — Leonarde Keeler adds the GSR channel to his polygraph, creating the three-channel design based on Summers' work [9]Verified A Review of the Polygraph: History, Methodology and Current Status
Comprehensive review confirming Keeler added GSR channel in 1938 based on Summers' work, and confirming polygraph development from Marston through Larson to Keeler[14]Verified A Review of the Polygraph: History, Methodology and Current Status (Keeler GSR Addition)
Confirms Keeler was the first to add the GSR channel in 1938, based on Summers' work at Fordham University.

1939 — Paul V. Trovillo publishes his definitive two-part 'History of Lie Detection' in the Journal of Criminal Law and Criminology [10]Verified Lie Detection: Its History, Methods and Techniques
Early comprehensive account of lie detection history documenting the transition from ancient ordeals to scientific instruments.

From Two Channels to Three

The pivotal moment when the psychogalvanometer became permanently linked to the polygraph came in 1938, when Leonarde Keeler (1903–1949) added a galvanic skin response channel to his polygraph instrument. Keeler was responsible for making the polygraph apparatus portable and was the first to add the GSR channel, based on the work of Fordham University psychologist Reverend Walter G. Summers [9]Verified A Review of the Polygraph: History, Methodology and Current Status
Comprehensive review confirming Keeler added GSR channel in 1938 based on Summers' work, and confirming polygraph development from Marston through Larson to Keeler[14]Verified A Review of the Polygraph: History, Methodology and Current Status (Keeler GSR Addition)
Confirms Keeler was the first to add the GSR channel in 1938, based on Summers' work at Fordham University.

Keeler had been working at Northwestern University's Scientific Crime Detection Laboratory (SCDL) since 1930, where he headed the polygraph department [13]Verified Teaching Forensic Science to the American Police and Public: The SCDL, 1929-1938
Confirms Northwestern University's Scientific Crime Detection Laboratory was established in 1929, Keeler headed polygraph department, and Inbau became director in 1938. The SCDL, established in 1929 in the wake of the St. Valentine's Day Massacre, was America's first independent forensic crime laboratory [13]Verified Teaching Forensic Science to the American Police and Public: The SCDL, 1929-1938
Confirms Northwestern University's Scientific Crime Detection Laboratory was established in 1929, Keeler headed polygraph department, and Inbau became director in 1938. It was in this environment of applied forensic science that Keeler made his transformative addition to the polygraph. Father Summers had developed a specialised version of the psychogalvanometer for criminal investigations in the mid-1930s and demonstrated promising results with approximately 50 criminal suspects [11]Verified Credibility Assessment: Scientific Research and Applications (EDA in Polygraph)
Confirms EDA was slow to be adapted to polygraph, Marston's 1917 EDA tests, Summers' advocacy, and Veraguth's observations on habituation. Keeler integrated this technology into his portable polygraph, creating the three-channel design — respiration, cardiovascular activity, and electrodermal activity — that remains the foundation of polygraph testing to this day [14]Verified A Review of the Polygraph: History, Methodology and Current Status (Keeler GSR Addition)
Confirms Keeler was the first to add the GSR channel in 1938, based on Summers' work at Fordham University. For more on Keeler's lasting contribution, see our history of the Keeler Polygraph Institute.

The Role of Fred Inbau and Northwestern University

Fred Inbau (1909–1998) joined the Scientific Crime Detection Laboratory in 1933 and became its director in 1938 when the laboratory was sold to the Chicago Police Department [15]Verified Fred E. Inbau (1909-1998) Papers
Confirms Inbau joined SCDL in 1933, became director in 1938, collaborated with John E. Reid on polygraph research, and was president of AAFS 1955–56. Though trained as a lawyer, Inbau was deeply interested in forensic science and became an early proponent of the polygraph [15]Verified Fred E. Inbau (1909-1998) Papers
Confirms Inbau joined SCDL in 1933, became director in 1938, collaborated with John E. Reid on polygraph research, and was president of AAFS 1955–56. He collaborated extensively with polygraph expert John E. Reid, and together they co-authored Truth and Deception: The Polygraph Technique (1966) [15]Verified Fred E. Inbau (1909-1998) Papers
Confirms Inbau joined SCDL in 1933, became director in 1938, collaborated with John E. Reid on polygraph research, and was president of AAFS 1955–56.

Inbau also served as president of the American Academy of Forensic Sciences (1955–56) and founded the Journal of Criminal Law, Criminology and Police Science [15]Verified Fred E. Inbau (1909-1998) Papers
Confirms Inbau joined SCDL in 1933, became director in 1938, collaborated with John E. Reid on polygraph research, and was president of AAFS 1955–56. His presence at Northwestern alongside Keeler ensured that the three-channel polygraph was not only developed but systematically tested and promoted within the broader forensic science community. Inbau's advocacy played a significant role in establishing polygraph testing as a legitimate forensic tool, a legacy that continued through the Cold War polygraph programs and into modern practice.

Exosomatic vs. Endosomatic Measurement

The two fundamental approaches to measuring electrodermal activity — established by Féré and Tarchanoff in the late 1880s — remain the basis for all modern electrodermal measurement. The exosomatic method (Féré's approach) applies a small external current to the skin and measures changes in conductance or resistance. The endosomatic method (Tarchanoff's approach) measures the skin's own internally generated electrical potential without any external current [1]Verified Electrodermal Activity
Confirms EDA history from Dubois-Reymond's 1849 observation, terminology standardisation, role of sympathetic nervous system, and that by 1972 over 1,500 articles had been published[16]Verified Publication Recommendations for Electrodermal Measurements (2012 Update)
Confirms the SPR committee report standardising EDA terminology and measurement procedures, updating the 1981 Fowles et al. recommendations.

In modern polygraph practice, the exosomatic method using direct current is by far the most common approach [16]Verified Publication Recommendations for Electrodermal Measurements (2012 Update)
Confirms the SPR committee report standardising EDA terminology and measurement procedures, updating the 1981 Fowles et al. recommendations. The examiner applies a constant low voltage (typically 0.5V) across two electrodes placed on the subject's fingertips and measures changes in skin conductance. This is the technique used in virtually all commercial polygraph instruments manufactured by companies such as Lafayette Instrument Company and its subsidiary Limestone Technologies [17]Verified Limestone Technologies — Polygraph Manufacturer
Confirms Limestone Technologies is a real polygraph manufacturer, now a subsidiary of Lafayette Instrument Company since August 2022.

The exosomatic DC method became the standard for polygraph applications because it produces clear, reliable skin conductance responses that correlate well with sympathetic nervous system arousal [16]Verified Publication Recommendations for Electrodermal Measurements (2012 Update)
Confirms the SPR committee report standardising EDA terminology and measurement procedures, updating the 1981 Fowles et al. recommendations. Understanding these distinctions is important for appreciating why modern polygraph equipment standards specify particular sensor configurations.

How EDA Works in the Body

Electrodermal activity (EDA) is the property of the human body that causes continuous variation in the electrical characteristics of the skin [1]Verified Electrodermal Activity
Confirms EDA history from Dubois-Reymond's 1849 observation, terminology standardisation, role of sympathetic nervous system, and that by 1972 over 1,500 articles had been published. The traditional theory 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 [1]Verified Electrodermal Activity
Confirms EDA history from Dubois-Reymond's 1849 observation, terminology standardisation, role of sympathetic nervous system, and that by 1972 over 1,500 articles had been published.

The eccrine sweat glands, densely concentrated on the palms and fingertips, are innervated exclusively by the sympathetic branch of the autonomic nervous system. When the sympathetic nervous system activates — in response to stress, fear, cognitive effort, or deception — these glands increase their output. Even microscopic increases in sweat production change the electrical properties of the skin surface, and these changes are detected by the EDA sensor on a polygraph instrument.

EDA reflects both slow-varying tonic sympathetic activity and fast-varying phasic sympathetic activity [1]Verified Electrodermal Activity
Confirms EDA history from Dubois-Reymond's 1849 observation, terminology standardisation, role of sympathetic nervous system, and that by 1972 over 1,500 articles had been published. Tonic activity is expressed as the skin conductance level (SCL), while phasic activity is expressed as skin conductance responses (SCR). In polygraph testing, it is primarily the phasic SCRs — rapid spikes in conductance following a relevant question — that examiners evaluate when scoring charts.

Electrodermal Non-Responders

One important consideration for polygraph practice that Veraguth first noted — individual differences in electrodermal reactivity — has significant implications for modern testing. Research has established that between 5% and 25% of the normal population may be classified as electrodermal non-responders, depending on the criteria used and the population studied [18]Verified Electrodermal Activity Patient Simulator (Non-Responder Data)
Confirms electrodermal non-responders represent between 5% and 25% of the normal population[19]Verified Guideline for Electrodermal Activity (COMFOCUS Protocol)
Confirms EDA non-responders estimated at 5-10% in general population and 25% in clinical populations. These individuals show little or no measurable electrodermal response even to strong stimuli.

Experienced polygraph examiners are trained to recognise non-responsivity during testing. The stim test (acquaintance or known-lie test) conducted at the beginning of an examination helps identify whether a subject shows normal electrodermal reactivity. If a subject shows no response to known stimuli, the examiner can adjust their scoring approach or consider additional physiological channels. Modern polygraph instruments record multiple channels precisely because no single measure is reliable for all individuals.

Standardisation of EDA Terminology

The long history of electrodermal research resulted in a confusing proliferation of names for the same basic phenomenon. Historically, EDA has 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) [1]Verified Electrodermal Activity
Confirms EDA history from Dubois-Reymond's 1849 observation, terminology standardisation, role of sympathetic nervous system, and that by 1972 over 1,500 articles had been published.

In 1981, the Society for Psychophysiological Research published a landmark committee report — authored by Fowles, Christie, Edelberg, Grings, Lykken, and Venables — that established standardised recommendations for electrodermal measurement [20]Verified Publication Recommendations for Electrodermal Measurements (Original 1981 Report)
Confirms the original 1981 Fowles et al. committee report standardising EDA methodology in Psychophysiology journal. This report formalised 'electrodermal activity' (EDA) as the preferred umbrella term encompassing all electrically measured skin phenomena, regardless of method. The 1981 recommendations were updated in 2012 by a new SPR Ad Hoc Committee led by Wolfram Boucsein [21]Verified Boucsein, W. (2012). Electrodermal Activity (2nd ed.)
Confirms the definitive textbook on electrodermal activity, second edition published by Springer, DOI: 10.1007/978-1-4614-1126-0, incorporating advances in measurement technology and ambulatory recording.

Modern Computerised Polygraph Instruments

Modern computerised polygraph instruments manufactured by companies such as Lafayette Instrument Company and its subsidiary Limestone Technologies digitise the analog EDA signal at high sampling rates [17]Verified Limestone Technologies — Polygraph Manufacturer
Confirms Limestone Technologies is a real polygraph manufacturer, now a subsidiary of Lafayette Instrument Company since August 2022[22]Verified LXSoftware by Lafayette Instrument Company
Confirms LXSoftware is bundled with OSS-3 scoring algorithm for computerised polygraph scoring. Lafayette's LX Software is bundled with the Objective Scoring System (OSS-3) computerised scoring algorithm [22]Verified LXSoftware by Lafayette Instrument Company
Confirms LXSoftware is bundled with OSS-3 scoring algorithm for computerised polygraph scoring, developed by Nelson, Handler, and Krapohl [23]Verified Brute-Force Comparison: OSS-3 and Human Polygraph Scorers
Confirms OSS-3 uses Kircher features including electrodermal amplitude, and that OSS-3 accuracy exceeded average human scorers. The OSS-3 uses digitised EDA features — including the amplitude of increase for electrodermal activity — as part of its mathematical classification [24]Verified Computerized Scoring of Polygraph Data (NAS Report Appendix F)
Confirms CPS and PolyScore as the two main computerised scoring systems reviewed by the National Academy of Sciences in 2003. Another widely used algorithm is PolyScore, developed at Johns Hopkins University Applied Physics Laboratory [25]Verified APA Standard for Polygraph Instrumentation
Confirms current APA instrumentation standards require electrodermal activity sensors alongside pneumograph and cardiovascular sensors.

These algorithms incorporate features first described by researchers at the University of Utah during the 1980s, now known as 'Kircher features' [24]Verified Computerized Scoring of Polygraph Data (NAS Report Appendix F)
Confirms CPS and PolyScore as the two main computerised scoring systems reviewed by the National Academy of Sciences in 2003. The electrodermal amplitude of increase is one of the key features these systems evaluate, demonstrating how Féré's 1888 discovery of skin conductance changes has evolved into a precisely quantified digital measurement used in forensic decision-making. For a deeper look at how these systems compare, see our guide to vintage analog polygraph instruments.

Why EDA Remains Central to Polygraph Testing

Electrodermal activity remains one of the most important channels in polygraph testing for several compelling reasons. First, EDA is driven exclusively by the sympathetic nervous system and cannot be voluntarily controlled [1]Verified Electrodermal Activity
Confirms EDA history from Dubois-Reymond's 1849 observation, terminology standardisation, role of sympathetic nervous system, and that by 1972 over 1,500 articles had been published. Unlike respiration, which a subject can consciously alter, skin conductance changes occur automatically in response to arousal. This involuntary nature — the same property that fascinated Féré, Jung, and Veraguth — makes EDA particularly valuable for deception detection.

Second, EDA produces clear, easily identifiable phasic responses that are relatively straightforward to evaluate. When a relevant question produces a significant skin conductance response, it is typically visible both to human scorers and to computerised algorithms. Third, the technology for measuring EDA is robust and reliable, requiring only two electrodes and a simple circuit — making it practical for field use in a way that more complex measurements may not be.

The American Polygraph Association's current instrumentation standards require that every polygraph system include a properly functioning electrodermal activity sensor alongside pneumograph and cardiovascular sensors. This three-channel minimum — the same basic configuration Keeler established in 1938 — reflects the enduring value of the electrodermal channel.

Factors That Can Influence EDA Measurement

As Veraguth noted over a century ago, individual differences in electrodermal reactivity exist and must be accounted for in any testing protocol. External factors such as temperature and humidity affect EDA measurements [1]Verified Electrodermal Activity
Confirms EDA history from Dubois-Reymond's 1849 observation, terminology standardisation, role of sympathetic nervous system, and that by 1972 over 1,500 articles had been published. Internal factors such as medications and hydration can also influence results [1]Verified Electrodermal Activity
Confirms EDA history from Dubois-Reymond's 1849 observation, terminology standardisation, role of sympathetic nervous system, and that by 1972 over 1,500 articles had been published. These are among the many factors that can affect polygraph results that trained examiners learn to manage.

Modern polygraph protocols address these challenges through standardised testing environments, proper electrode preparation, and the use of multiple physiological channels. The multi-channel approach that Keeler pioneered ensures that if one channel produces ambiguous results for a particular individual, other channels may still provide clear data. This redundancy is one of the key strengths of the modern polygraph instrument.