Electrodermal ActivityAn EDA Primer for Polygraph ExaminersMark Handler, Raymond Nelson, Donald Krapohl, and Charles R. HontsDespite the pragmatic simplicity androbustness of EDRs, the psychophysiologicalmechanism underlying them is complex andincompletely understood (Lykken & Venables,1971). Unfortunately, there are manymisconceptions of the EDR with the polygraphprofession and elsewhere. This paper isoffered as a primer/reference on EDR for thepracticing and student polygraph examiner.We describe the present state of the scientificknowledge of the integumentary system andEDRs, and provide a description of the use ofEDRs in the science of PsychophysiologicalDeception Detection (PDD) testing. The paperis organized along natural divisions, and leadsthe reader from history, through physiology,to the latest scientific understandings andfinally arrives at what most examinersconsider the most interesting — how to applythe EDR to deception detection.IntroductionOf all the signals collected andanalyzed during psychophysiological detectionof deception (PDD) or polygraph testing, theelectrodermal response (EDR) is the mostrobust and informative. The EDR is easilycollected and is simple to measure andinterpret (Blalock, Cushman & Nelson, 2009).Several studies indicate the electrodermalcomponent provides the greatest contributionto diagnostic accuracy in the comparisonquestion test (Blalock, Cushman & Nelson,2009; Capps & Ansley, 1992; Harris & Olsen,1994; Kircher & Raskin, 1988; Krapohl &Handler, 2006; Krapohl & McManus, 1999;Nelson, Krapohl & Handler, 2008; Raskin,Kircher, Honts, & Horowitz, 1988). The basicpremise underlying the interpretation of EDRsis that the magnitude of response iscommensuratewiththedegreeofpsychological importance that the examineeimparts to each stimulus question duringtesting. Peterson (1907), a student of thefamous psychologist Carl Jung wrote: “It islike fishing in a sea of the unconscious, andthe fish that likes the bait best jumps to thehook.Every stimulus accompanied by anemotion produced a deviation of thegalvanometer to a degree of direct proportionto the liveliness and actuality of the emotionaroused” (p. 805).Terminology1The term electrodermal activity (EDA)is a relative newcomer and was firstintroduced in 1966 by Johnson and Lubin(1966). Johnson and Lubin (1966) proposedits use as an umbrella term under which allelectrical phenomena in skin might besubsumed. Brown (1967) and Venables andMartin (1967a) proposed the standardMark Handler, American Association of Police Polygraphists; Raymond Nelson, Lafayette Instrument Company;Donald Krapohl, American Polygraph Association; Charles R. Honts, Boise State University.1 The material in this section is derived from the major scientific sources describing the terminology of electrodermalactivity. Readers interested in the original scientific sources should see Boucsein, 1992.Authors’ NoteThe authors are grateful to Professor Wolfram Boucsein, Dr. George Deitchman, Chris Fausett, WaltGoodson, Ed Hoffman, Don Imbordino, Dr. John Kircher, Pam Shaw, Brent Smitley, and Jim Wygant for theirthoughtful reviews and comments to earlier drafts or sections of this paper. The views expressed in this article aresolely those of the authors, and do not necessarily represent those of the American Association of PolicePolygraphists, Lafayette Instrument Company, the Defense Academy for Credibility Assessment, Boise StateUniversity or the American Polygraph Association. Questions and comments are welcome [email protected]. This manuscript is dedicated to Professor Wolfram Boucsein, a great educator, scientist,author and friend who wrote the modern treatise on electrodermal activity.Polygraph, 2010, 39(2)68

Handler, Nelson, Krapohl & , which is still used today in thescience of psychophysiology.baseline level at any given moment, while EDRis reserved for the phasic response orreactions to stimulation. The designators Rand L may be appropriately applied to the typeof measurement taken, for example SRR (skinresistance response) or SCL (skin conductancelevel) (See Table 1.) Spontaneous or nonspecific EDRs (NS.SCR and NS.SRR) are thosethat cannot be attributed to an identifiablestimulus. Differential amplifiers can also beused to directly measure the electrical activitygenerated by the sweat glands. That approachto measuring EDA is referred to as anendosomatic measurement and the resultantmeasure is known as Skin Potential which ismeasured in micro-volts (µV).Electrodermal recordings that apply avoltage or current to the skin are calledexosomatic and in polygraphy a direct current(DC) is used to measure aspects of EDA.Constant voltage DC systems record EDA asskin conductance (SC) for which the units areSiemens (S) or mhos, which is the inverse ofohm in both spelling and in computation.Constant current systems measure and recordskin resistance (SR), which is measured inohms. EDL is the accepted abbreviation forelectrodermal level and refers to the tonic orTable 1. Abbreviations for electrodermal recording methods, units of measurementand recording methodAbbreviationMeasurementUnits of MeasureRecording MethodEDAElectrodermal ActivityVaries by methodVaries by methodEDL (tonic)Electrodermal LevelVaries by methodVaries by methodEDR (phasic)Electrodermal ResponseVaries by methodVaries by methodSCL (tonic)Skin Conductance LevelSiemens or mhoExosomaticSCR (phasic)Skin ConductanceResponseSiemens or mhoExosomaticSRL (tonic)Skin Resistance LevelOhmsExosomaticSRR (phasic)Skin Resistance Response OhmsExosomaticSPL (tonic)Skin Potential LevelMicro-voltsEndosomaticSPR (phasic)Skin Potential ResponseMicro-voltsEndosomaticVarious suffixes may be added to theabbreviations to further describe features ofthe phasic component: amplitude (e.g., SRRamp) would describe the height of a singleresponse and latency (e.g., SRR lat.) woulddescribe the time delay from stimulus tobeginning of response. There are a largenumber of features that can be measuredfrom the EDR; many were described in detailby Kircher and Raskin (1988).Galvanic skin response or galvanicskin reflex (GSR) is an outdated andincomplete term (Boucsein, 1992). A galvaniccell is one that uses a chemical reactionresulting from electrical contact between two69Polygraph, 2010, 39(2)

Electrodermal Activitydissimilar metals to produce an electricalcurrent. The term GSR implies the skinfunctions as a galvanic cell, which isinconsistent with how the EDR is obtained inmodernpolygraphywithexosomatictechnology. Additionally, the term reflex infersthat EDRs are reflexive in nature which isinconsistent with the notion of psychologicallyelicited EDRs that are thought to be the resultof an emotional response to, or cognitiveappraisal of, verbal test stimuli during PDDtesting. The Galvanic Skin Response (GSR)was named for Luigi Galvani, an Italianphysician and physicist who found that byattaching the legs of a frog to dissimilarmetals or an electrical source, he could makethem twitch and move. The discovery thatdissimilar metals could produce an electricalcharge later led to the development of thebattery, though not by Galvani. Thephenomenon of electrical activity observed inthe skin has inaccurately borne the GSR labelfor many years and nothing is gained byretaining this archaic term.Russian physiologist Tarchanoff (1889)was one of the first to report changes in skinpotential measurements following a variety ofsensory and physical stimuli. Tarchanoffcorrectly attributed these changes to sweatgland activity. Féré (1888) found changes inresistance to a number of stimuli using aconstant current model, and is thus creditedwith the discovery of exosomatic EDRrecording. Féré, however, was convinced thechanges in resistance were a result ofvasomotor changes, a theory which is nolonger considered viable2.In 1906 Veraguth published amonograph entitled The Psychogalvanic ReflexPhenomenon in which he focused on EDRs aspsychophysiological events. Richter (1929)was one of the earliest investigators to proposethat endosomatic EDA (skin potential) owedits cause to sweat gland activity andepidermal mechanism (Boucsein, 1992).Advances in equipment development throughthe 1900s allowed for better measurementand recording of EDA. Polygraphs, advancesin electronics, and much later, computersimproved on the ability to store and analyzedata electronically that had been recordedsimultaneously from numerous sites.HistoryStudies on changes in electricalproperty of the skin can be traced back to theworks of Germany's DuBois-Reymond in 1849and that of French neurologist Jean Charcotin the late 1800s (Boucsein, 1992). One of theearliest documented experiments showing arelationship between sweat gland activity andcurrent flow in the skin was performed byHermann and Luchsinger (1878) who reportedan association between electrical nervestimulation and foot pad sweat secretion in acat (Boucsein, 1992). Hermann was one of thefirst to note that the palmar and finger areasof the hand showed greater responses thanother body areas, a first step towardappreciating the areas with the greaterdensities of sweat glands. Boucsein (1992)credits Vigouroux (1879) with the earliestassociation of EDRs and psychological stimuli.Attempts at detecting deception withthe aid of scientific instruments can be tracedto the 1890s when Cesare Lombroso (Trovillo,1939) used pulse rate and possibly bloodpressure changes to infer deception. HugoMunsterberg (1908) made some of the earliestsuggestions for use of instrumentation indeception testing in legal cases. ists to research the phenomena ofpsychophysiology but cautioned against anyrush to judgment or use, as he foresaw thedeceptive subjects. Marston employed aspecificity to deception problem clearly andearly on. In approximately 1914, Benussireported observing differences in inhalation-We now know that the vasomotor center is a cluster of sympathetic neurons in the medulla concerned with theregulation of blood vessel resistance. Vasomotor activity causes changes in the sympathetic fibers regulating thisresistance by changing the degree of contraction of the smooth muscle in the walls of the blood vessels. Changes inmuscle contraction results in changes in vessel diameter which is what modifies the resistance. Increasedsympathetic activation results in increased contraction and raises the resistance of the vessel. While vasomotoractivity is often a covariant with EDR, they are separate processes.2Polygraph, 2010, 39(2)70

Handler, Nelson, Krapohl & Hontsexhalation ratios between truthful anddiscontinuous blood pressure measurement todetermine when an examinee was engaging indeception, a practice that became the focus ofthe famous case of the United States v. Frye.The Frye decision ultimately set the standardfor the introduction of scientific evidence intolegal proceedings in the U. S. Federal Courtsfor 70 years. Larson combined aspects of theBenussi and Marston approach, improving onboth in terms of instrumentation and theory.Larson developed a polygraph capable ofrecording continuous relative blood pressurepressure changes, pulse rates and movementassociated with breathing in 1921 (Trovillo,1939).garnered enthusiastic support only fromthe creator of the technique. ReverendSummer'sPathometerencounteredlimited general use.” (p. 7).Leonarde Keeler is commonly givencredit for adding the EDR component, therecording of respiration, and relative bloodpressure as early as 1949 (Reid & Inbau,1977). Trovillo (1939), reported that Wilson, acolleague of Keeler, actually developed apolygraph that simultaneously recorded thethree channels of respiration movement,cardiograph and electrodermal activity inapproximately 1930. With the exception of aphotoelectric device to record vasomotorchanges, these components have remainedthe primary psychophysiological channels fordetection of arousal associated with deceptionsince the 1930s.One of the earliest records of the use ofEDRs to detect deception was by AlfredStickler in approximately 1897, which hedescribed in his contribution to Carl Jung'sbook Studies in Word Association (1919).Larson (1932), credits Chester Darrow withadding a skin resistance measurement toearly polygraphs and experimented with agalvanometer himself, but reportedly decidedto forego its use in favor of cardiographic-typeresponse measurement. Marston (1938),reportedly experimented with the EDRcomponent while devising deception tests forthe United States Army in 1917, but wrotethat he was unimpressed with the lack ofspecificity to deception. Marston realized thatnumerous emotional arousals could, and did,cause EDRs.Anatomy and Physiology of the Skin3The skin is called the integumentarysystem and consists of a complex set oforgans that provide protective and sensefunctions. Skin protects the body fromenvironmental threats such as temperature,chemical, mechanical and infectious agents byacting as a selective barrier. Skin can aid inthe removal of substances like water andsolutes from the bloodstream through thesweat glands. From a sensory standpoint, skinhouses various receptors to provide afferentinformation related to touch, pain andtemperature (Venables & Christie, 1973).Reverend Walter Summers (1936),reported high levels of sensitivity to deceptionwhen using EDR measurements in both alaboratory setting and in limited criminal fieldapplications. Krapohl (1993) comments;In many areas, skin allows forperspiration, which helps keep the skin moistand may contribute to flexibility, though thisis less likely on the plantar and palmarsurfaces (soles of the feet and palms of thehands). These areas have increased potentialto be subjected to load bearing and frictionand are considerably thicker, 600 microns ascompared to the 15 microns found in manyother areas (Venables & Christie, 1973). Skinalso helps maintain a constant bodytemperature by controlling heat loss which is“Summers usedhisdevice andtechnique on only about 50 criminalsuspects and he claimed tremendoussuccess, though his verification of thoseresults would not stand up to currentstandards of proof. His work, like thatof Lombrosso and Marston, hadThe material in this section is derived from the major scientific sources describing the Anatomy and Physiology ofthe skin (e.g. structure of the skin). Readers interested in the original scientific sources should see: Boucsein, 1992;Fowles, 1986; and Venables & Christie, 1973.371Polygraph, 2010, 39(2)

Electrodermal Activityregulated by adjusting blood flow to areasnear the surface of the skin and throughthermoregulatory sweating. Increasing bloodflow near the surface allows for cooling of thepassing blood and this cooling is then passedon to lower lying tissue. Thermoregulatorysweating cools the surface of the skin byremoving the latent heat when liquid waterevaporates on the surface of the skin. Atpalmar and plantar sites thermoregulatorysweating occurs only in relatively highambient temperatures (upper 80s F). Sweatglands on the soles and palms are moreresponsive to central nervous system (CNS)activation than to ambient temperaturechanges.include; nerve cells called Meissner's andVater-Pacini corpuscles that transmit thesensations of touch and pressure, hairfollicles with their associated oil and scentglands, erector pili muscles that attach toeach hair follicle, blood vessels and nervesthat transmit sensations of pain, itch, andtemperature, and eccrine sweat glands, whichare the putative source of EDRs.Beneath the dermal layer lies thesubcutis, also called the hypodermis, whichattach the skin to connective tissue coveringthe muscles. This is also where the secretorypart of the eccrine sweat gland may lie, alongwith blood vessels and nerves supplying therest of the skin. When located here, thesecretory portion of the eccrine sweat gland isembedded in fatty tissue and is supplied bythe capillary network of that area with waterand electrolytes (Boucsein, 1992). For thelocation of these structures, as well as thegeneral location of the various layers of skin,see Figure 1.Skiniscomposedofvariouscharacteristic layers, though all layers are notuniformly found in all skin. Skin can be hairyor glabrous (hairless). Skin essentiallyconsists of two main layers; an outer layercalled the epidermis and a thicker lower layer,the dermis. The epidermis of glabrous skin asfound on the palm is generally divided intothree regions which compose five layers witheach layer becoming progressively tougherand calloused toward the surface. Thestratum malpighii region is comprised of thetwo deepest layers of the epidermis which arethe strata germinativum, and spinosum. Thestratum intermedium region consists of thestratum granulosum, and stratum lucidum.The latter is recognizable in limited body sites,primarily in palmar and plantar skin and isvisible only if the horny layer is removed. Theoutermost region is called the stratumcorneum and can be divided into a lower,middle and upper zone based upon the formof the cells and the space between the cells,which decreases as it approaches the surface(Boucsein, 1992).Sweat Gland Types, Distribution andProperties4Humans have two basic types of sweatglands, apocrine and eccrine. Apocrine sweatglands are large in size, discharge into hairfollicles, and become active during puberty.They are mainly found in the armpit andgenital areas and are not the source of theEDRsmeasuredandevaluatedinpsychophysiology or polygraphy. Eccrinesweat glands, on the other hand, aredistributed throughout the body, but most areconcentrated on the palms, soles and foreheadand least dense on the arms, trunk and legs.Estimates place the number of eccrine sweatglands between 2 and 5 million (Fowles, 1986)and the total number of sweat glands is fixedat birth.The thicker layer of skin, the dermis,consists of two main parts; the papillary layerwhich contains a thin arrangement of collagenfibers and the thicker reticular layer, of thickcollagen fibers that are arranged parallel tothe surface of the skin. The dermis containsmany specialized cells and structures. TheseThey are called eccrine because theycontain comparatively little gland cellcytoplasm(thewaterbased,jelly-likesubstance that fills the cell). The eccrine sweatgland consists of a coiled secretory portionThe material in this section is derived from the major scientific sources describing sweat gland physiology anddistribution. Readers interested in the original scientific sources should see: Boucsein, 1992; Fowles, 1986; andVenables & Christie, 1973.4Polygraph, 2010, 39(2)72

Handler, Nelson, Krapohl & HontsFigure 1. Anatomy of the skin. Pope, Amy E. Anatomy and Physiology for Nurses (New York: G. P.Putnam's Sons, 1913) 439. Clipart courtesy FCIT, Retrieved 9February, 2010, from skin.htm.(glomerulus) about .4 mm in diameter (seeFigure 2) located in the subdermis and aductal discharge tube that winds its waythrough the dermis and then follows a spiralcourse through the epidermis terminating at apore on the skin surface. Both the secretoryand most of the ductal segments are formedby two-to-three layers of cells (Figure 2). Thewall of the ductal tube that passes throughthe epidermis is called the acrosyringium andit has no cells in its walls. Essentially it is acoiled duct surrounded by yringium has no wall cells (see Figure 2),it is possible for sweat working its way up theduct through the epithelium to escape theductal tube without being deposited on thesurface and hydrate the corneum (Fowles,1986). If the corneum adjacent to theacrosyringiumisadequatelyhydrated,discharge from the tube may then be directedto the surface of the skin. As the corneumbecomes hydrated with ion-laden sweat, itsability to conduct a current will increase.When the sweat glands are completely full ofsweat, however, the electrical conductance ofthe skin is presumed to increase markedly(Boucsein, 1992).73Polygraph, 2010, 39(2)

Electrodermal ActivityFigure 2. Layered construction of human skin shown in relation to the eccrine sweat glandincluding the secretory portion, the straight duct and the acrosyringium. Adapted from Chancellor,William E. Standard Short Courses for Evening Schools (New York: American Book Company, 1911)244. Clipart courtesy FCIT, Retrieved 9 February, 2010, from skin.htm.The Sweating Action of the Eccrine SweatGlands5study them individually. The sudorisecretoryfibers surround the secretory part of theeccrine sweat gland and use acetylcholine forinnervation. No synaptic clefts have yet beenidentified and it is presumed that theneurotransmitter substance is released in thevicinity of cholinergic receptors on thesecretory cells resulting in their depolarizationand activation (Boucsein, 1992).Efferent fibers from the sympatheticnervous system innervate the eccrine sweatglands secretory segment and dermal portionsof the duct. These sudorisecretory fibers areintermeshed with fibers innervating piloerector muscles of the hair and fibers thatinnervate blood vessels, making it difficult toThe material in this section is derived from the major scientific sources describing sweating action of eccrine sweatglands. Readers interested in the original scientific sources should see: Boucsein, 1992; Fowles, 1986; and Venables& Christie, 1973.5Polygraph, 2010, 39(2)74

Handler, Nelson, Krapohl & HontsHuman precursor sweat containsrelatively high concentrations of sodium (Na ),potassium (K ) and chloride (Cl-), all of whichare vital to life. By the time the sweat reachesthe surface of the skin, the concentration ofthose very important ions has been reduceddrastically, presumably through the processesof active and passive reabsorption. Activereabsorption has been compared to the sameaction that occurs in the renal tubules of thekidneys (Boucsein, 1992). Relative to theinterior of the body, sweat has fewer ions ofsodium and chloride and is thus referred to ashypotonic. The concentration of surface sweatvaries with the rate of sweating, presumablyreflecting a limited reabsorption capacity(Fowles,1986).Theincreasedionconcentration during higher sweat rates maycontribute to EDA changes. Reabsorption isthought to take place primarily in the dermalduct but also in the acrosyringium. Throughthe process of reabsorption, sweat gland ductsmay help to protect the body from excessiveion loss during periods of profuse sweating.There is considerable evidence to suggest thatsodium is reabsorbed via an active sodiumpotassium pump. Sodium is exchanged withpotassium resulting in an increase inpotassium concentration in surface assivelydiffusesdownitselectrochemical gradient to be reabsorbed(Fowles, 1986). While the chemical chlorideion gradient tends to oppose diffusion, thesomewhatgreaterelectricalpotentialfacilitates it, resulting in passive ine. When the coil contracts, thelumen dilates slightly and stays dilated untilthe innervation ceases. Presumably, thiscontraction of the glomerulus and dilation ofthe lumen contribute to movement of thesweat up the duct towards the surface of theskin. Sweat does not flow constantly from thesecretory portion of the gland onto the skinsurface. Rhythmic contractions of cellssurrounding the secretory and ductal part ofthe gland have been observed to create sweatpulses at rates of around 20 cycles per second(Boucsein, 1992) which may help move thesweat up the duct towards the surface pore.Suggested Biological Significance of EDA6The biological significance associatedwith EDRs has been proffered in terms ofevolutionary benefits. Explanations of thebenefits of EDRs seem consistent with anumber of psychological underpinningsdiscussed later in this paper. Edelberg (1972)suggested that thermoregulatory responses toemotionallyarousingstimulimaybeallostatic7 in nature. Evaporative sweatingmay serve to decrease body temperature inanticipation of an upcoming burst of physicalactivity. Emotionally arousing stimuli, resultin vaso-constriction which leads to areduction in skin blood flow. An adaptivepurpose of this vasoconstriction is to increasesystemic blood pressure for increased largemuscle perfusion. There is an additionalbenefit of reducing cutaneous blood lossshould a cut occur during the state of arousal.Cutaneous blood flow plays a part in thermalregulation so a reduction in surface blood flowcould lead to a rise in body temperature.Perhaps evaporative cooling via EDRs helpscompensate for the reduction in heat lossresulting from vasoconstriction.Sato (1977) discovered that whensecretory coil is not being stimulated, thelumen is almost completely collapsed. Thiswould suggest there was an insufficientquantity of pre-formed sweat in just theresting lumen to reach the sweat pore openingand cause EDRs without some sweatcontribution from the glomerulus. What Satodiscovered was that when the glomerulus(secretory coil) is innervated, it contracts toabout two-thirds of its original length within aIncreased palmer perspiration mayallow for better tactile differentiation (Darrow,1933), better hand grip (Boucsein, 1992;Darrow, 1933), and protection against injuryThe material in this section is derived from the major scientific sources describing some of the possible biologicalsignificance of sweat glands. Readers interested in the original scientific sources should see Edelberg, 1967.6Allostatic refers to the maintenance of homeostasis through physical or behavioral response. A resource for readersinterested in allostasis as it relates to polygraphy can be found in Polygraph, 37(3), 228-233.775Polygraph, 2010, 39(2)

Electrodermal Activity(Adams & Hunter, 1969). Increased g, 1967; Boucsein, 1992) an obviousbenefit to bare foot runners and tree climbingprimates.electrical current to flow directly) from thesurface of the skin to and through therelatively moist dermal layers. For any givenlevel of corneal hydration, changes in theheight of the sweat in the duct will modify theresistance across the corneum: the ductworks like a variable resistor. Edelberg (1983)demonstrated how the level of sweat in theduct at innervation has a marked effect onEDR amplitude. Edelberg manipulated thelevel of sweat in the duct prior to innervatingthe gland and measured the results. Theconclusion was that higher initial levels ofsweat in the duct produced EDRs of greateramplitude, in fact at times tripling theresponse.EDA and the Electrical Properties of Skin8There is ample empirical evidence tosupport the notion that sweat gland activitycontributes to the phenomena of EDA, emodelforexplanation. Sweat moistened epidermaltissue contains ions which increases skinconductivity. The layers of skin below theepidermis show good electrical conductivityand do not contribute to skin resistancechanges measured during an EDR (Boucsein,1992). Most electrical models of skin assignthe role of a variable resistor to the entirestratum corneum, relative to its degree ofhydration. The dead cells of the stratumcorneum act like a sponge, taking in moisturefrom above (outside the body or from anyelectrolyte solution) and below (from withinthe body). The stratum corneum is usuallypartially hydrated and the degree to which itis hydrated will be the primary contributor toEDL. Changes in corneal hydration willgenerally result in tonic level changes of EDA,but also have an effect on the amplitude ofEDR (Fowles, 1986). Increased hydrationreduces resistance and increases conductancewhile a drier stratum corneum worksoppositely. When the corneum is eitherextremely hydrated or extremely dehydrated,EDRs are minimal. It is at intermediate levelsof corneal hydration that maximal levels ofEDRs are achieved (Stombaugh & Adams,1971).There are many proposed theories andmodels of the electrical properties of the skinand a number of those were reviewed byEdelberg (1972). No single model is completelytenable and stands on its own but mostaccept some general facts. EDRs require thepresence of active sweat glands. This fact thathas been substantiated by interrupting thesympathetic nerve supply to the sweat glandthrough chemical blockage or sympathectomy,as performed in efforts to alleviate a conditionknown as hyperhidrosis. In either case, theseaffect EDRs at the interface between the sweatgland and the sympathetic cholinergicinnervation occurring there. Beyond thispoint, it becomes difficult to specifically pointto the mechanism responsible for EDRs.Edelberg (1972) suggested the capacitanceproperties of the skin and sweat glandscontributed to the fast rise, phasic EDRs.When an external current is applied to theskin, the cell membranes can store electricalpotentials like a capacitor. Edelberg (1971)posited that larger cell assemblages may acttogether to selectively allow passage of certainions as if they were parallel capacitors. Thusthe phasic EDR response observed inpolygraphy could in part be due to membranedepolarization when the cells are collectivelyneurologically stimulated. The capacitiveproperties of skin and sweat gland ducts havenot been well investigated compared to thosethat are resistive in nature. This may be dueSweat secretions result in not onlycorneal hydration but also in filling of thesweat duct. Both duct filling and cornealhydrationleadtochangesinskinconductance, though duct filling is theprimary mechanism by which EDRs areelicited (Fowles, 1986). Filling the ductsresults in direct electrical shunts (allowsThe material in this section is derived from the major scientific sources describing the electrical properties of skin.Readers interested in the original s

An EDA Primer for Polygraph Examiners Mark Handler, Raymond Nelson, Donald Krapohl, and Charles R. Honts Introduction Of all the signals collected and analyzed during psychophysiological detection of deception (PDD) or polygraph testing, the electrodermal response (EDR) is the most robust and inform