A Comparison Between Commercially Available Electrode Gels and Purpose-Made Gel, in the Measurement of Electrodermal Activity

Despite general agreement that a standardised procedure is desirable for the measurement of electrodermal activity, several types of electrode gel are in common use. In this study, 20 volunteers listened to a series of tones while skin conductance was measured at four sites using four different gels, namely K-Y Jelly, Beckman, Neptic, and purpose-made 0.05M NaCl in methyl cellulose. Prestimulus conductance level, response amplitude, change in conductance level, response latency, and response probability were measured. Analysis of variance showed a significant between-gels effect for prestimulus conductance levels, with Beckman and Neptic giving higher levels than K-Y Jelly or 0.05M, as predicted. There were no between-gels effects for the other variables. There were no effects due to placements or channels. The results are discussed in relation to the theoretical requirements of electrode gels used for measuring electrodermal activity.     

Electrodermal Activity Recorded Concomitantly From the Subject's Two Hands

Electrodermal activity is the most frequently monitored psychophysiological and most investigators assume that the activity recorded from one hand is representative of the whole system. A few earlier studies of possible bilateral differences in this activity frequently noted such differences in response magnitude and pre-response level. The present study examines bilateral differences not only in response magnitude and pre-response level but also in response latency, recruitment time, and recovery. Relationships with handedness are also considered. It is concluded that although bilateral differences were often noted, the activity from one hand is strongly related to the activity concomitantly recorded from the other hand.     

An Automatic Voltage Suppressor For the Measurement of Electrodermal Activity

An automatic voltage suppressor is described which increases the resolution of skin conductance and/or skin potential responses, facilitates the measurement of the corresponding levels, and prepares both electrodermal quantities for automatic data processing. The device accomplishes: 1) scanning of the levels at preset moments, 2) digital storing of these values for the corresponding time intervals, 3) subtraction of the stored values (minus an adjustable reserve) from the input signals, and 4) amplification of the difference voltages. Easy and inexpensive construction of the apparatus is possible using a minimal number of highly integrated circuits.     

The Relationship of Symptomatology and Medication to Electrodermal Activity in Schizophrenia

An electrodermal assessment procedure using mild innocuous tones, task-relevant tones, and loud white noise was administered to a sample of schizophrenic patients (n = 77). The present study investigated the relationship of schizophrenic symptomatology and anticholinergic level of neuroleptic medication to electrodermal variables. Each patient was evaluated for positive (florid) and negative (defect) symptoms. The neuroleptics that patients received were rated according to their anticholinergic effect. No significant differences in symptomatology were observed between electrodermal responders and nonresponders; however, nonresponders showed a nonsignificant tendency to have more positive and negative symptoms than responders. Both negative symptoms and anticholinergic levels were significant predictors of lower tonic levels of skin conductance. Patients receiving high anticholinergic neuroleptics showed significantly reduced measures of electrodermal responsivity and tonic levels. Thus, both symptomatology and type of neuroleptic are related to electrodermal measures, with the anticholinergic effect of neuroleptic medication being more pronounced.     

A Major Effect of Recording Site on Measurement of Electrodermal Activity

Although the medial phalanx has been recommended as the preferred site for recording skin conductance activity, a review of articles published in Psychophysiology indicates that a large minority (34%) of studies employ the distal phalanx. Informal observations also suggest that the distal site may be more reactive than the medial site. This study formally tests this observation by recording skin conductance from both medial and distal phalanges. Twenty-four right-handed subjects (12 male, 12 female) were exposed to a series of 10 orienting and defensive stimuli. Electrodes were placed on the fore and middle fingers of each hand, with distal sites used on one hand and medial sites on the other for each subject. Skin conductance amplitudes were 3.5 times larger at distal than medial sites (p less than .002), while skin conductance levels were 2.08 times larger at distal sites (p less than .0005). A significant Site X Stimulus interaction (p less than .025) indicated that the distal site was more sensitive to habituation over trials and to increases in skin conductance amplitudes with increasing stimulus intensity than the medial site. On the basis of these findings it is recommended that distal sites be used in preference to medial sites in the recording of skin conductance activity.     

Videotape technology in the identification and storage of intracerebral electrode locations.

Using standard videotape recording (VTR) equipment and a modified optical system, it is possible to identify and record the location of surgically implanted electrodes with picture and sound. No special chemicals or darkroom procedures are required.     

Bilateral Electrodermal and Electrocortical Activity in Anticipation of Sensorimotor Tasks

The present study investigated the relationship between lateralized sensorimotor activation and lateralized elevation of electrodermal activity. Within a two-stimulus reaction time paradigm skin conductance responses (SCRs) were recorded from both hands, while subjects awaited and performed unilateral sensorimotor tasks. A tactile warning stimulus was applied 6 s prior to a tactile imperative stimulus either to the same or to the contralateral hand; the imperative stimulus was associated with a choice reaction time task. Task-dependent lateral asymmetry with larger skin conductance responses contralateral to the involved hemisphere indicated contralateral facilitatory processes rather than inhibition. This asymmetry disappeared with repeated stimulation (across trials). Only right-hand (left hemispheric) tasks proved to be sensitive to habituation. The asymmetry, recorded in slow brain potentials (SP_s), assured that lateralized cortical processing was induced through the present experimental arrangement. The brain potentials specified the time course of lateralized processing, exhibiting larger late negative shifts at the precentral areas contralateral to the hand involved in the sensorimotor task and larger early negativity and a more pronounced positive evoked potential (late positive complex, LPC) contralateral to the hand stimulated by the tactile warning stimulus.     

The relationship of sweat gland count to electrodermal activity

This study assessed whether greater skin conductance activity at the distal versus medial site (Scerbo, Freedman, Raine, Dawson, & Venables, 1992) is attributable to a greater number of active (open) sweat glands at the distal site. The number of sweat glands was measured using the Palmar Sweat Index (PSI). Twenty-four subjects were exposed to 10 auditory stimuli. Electrodes were placed on the fore and middle fingers of each hand, using distal sites on one hand and medial sites on the other. The PSI was measured at the medial and distal phalanges adjacent to the electrode placement sites. The distal site contained more open and total sweat glands. Open gland count had the strongest correlations with skin conductance. Multivariate analyses of covariance revealed that site effects for nonspecific and orienting response frequency and trials to habituation were associated with site differences in open glands. Skin conductance measures and the PSI reveal greater electrodermal activity at the distal site. In addition, the number of open glands may be a useful measure related to electrodermal response frequency when polygraph measurement is unavailable.     

Hemispheric Asymmetry and Bilateral Electrodermal Recordings: A Review of the Evidence

Bilateral electrodermal recordings are often used in psychophysiological research as a measure of functional hemispheric asymmetry. Although significant differences between left and right hand recordings are reported in the literature, the obtained differences are often in different directions. The purpose of the present paper was to review empirical evidence related to the issue of bilateral electrodermal recordings in research on hemispheric asymmetry. Special reference is made to the current controversy concerning contralateral inhibition vs. excitation or facilitation as the underlying mechanism for reported differences in performance of typical hemisphere-specific tasks. After reviewing the evidence, which is contradictory concerning several of the more critical parameters, the conclusion is that bilateral electrodermal recordings have not been unambiguously related to hemispheric asymmetry. However, when asymmetry between the hands is clearly demonstrated, this reflects an asymmetry in the functioning of the cerebral hemispheres.     

Parental Psychopathology, Age, and Race as Related to Electrodermal Activity of Children

The purpose of this investigation was to determine whether parental psychopathology, age, and race affected electrodermal activity (EDA) and to examine relationships between psychopathology and EDA. Children of hospitalized schizophrenic, manic-depressive, physically ill, and non-ill (non-hospitalized) parents were compared on five factors of EDA and one of body movement. The factors were derived from EDA and movement artifact data recorded during a habituation-conditioning paradigm. Results indicated that parental illness (mental or physical) was not related to EDA, but children of psychotics had more movement during the experimental session than control children. Younger children showed greater responsiveness and more movement than older children. White children had more nonspecific activity than did black children. Significant but low correlations were found between EDA and pathology ratings made on the basis of psychiatric and psychological examinations. If both are prodromal signs of psychiatric illness, then at least within this age range, they appear to be quite different measures of predisposition to psychiatric disorder.     

Unconfounded Electrodermal Measures in Assessing the Aversiveness of Predictable and Unpredictable Shocks

The effect of temporal information on the electrodermal response to an aversive stimulus (shock) was evaluated. Eighty female volunteers were presented with trials in which the onset time of an aversive shock was either predictable or unpredictable. Following each trial, subjects indicated the degree of distress they felt while they were waiting for the shock to occur, and the perceived aversiveness of the shock at its impact. Skin resistance was recorded continuously. The responses produced by the predictable shocks were smaller than those produced by the unpredictable ones. Self-report measures also followed this trend; more people preferred the predictable condition. Information about the timing of an aversive event appears beneficial for people both at a subjective and at an autonomic level.     

The Relationship of EDA to Electrode Size

The pari passu relationship between contact area of electrode and SCLs and SCR amplitudes which is predicted on the basis of current electrical models of EDA was investigated in a series of experiments employing a wide range of commonly used contact areas: .017 to .786 cm² (.15 to 1.0 cm diameter). Having systematically eliminated obvious methodological and procedural problems a nonmonotonic relationship remained. On the basis of these findings two recommendations were made: 1) the use of an intermediate size, .5 cm² (.80 cm diameter), of electrode in recording EDA; 2) SCLs and SCR amplitudes should be reported in terms of actual electrode size rather than specific conductance units as previously suggested. No effect of electrode size was found for time-based measures of EDA. Results are discussed in terms of practical implications.     

Ambulatory Electrodermal Monitoring: Effects of Ambient Temperature, General Activity, Electrolyte Media, and Length of Recording

The feasibility of long-term monitoring of electrodermal activity (EDA) from freely moving subjects was assessed by examining several confounding variables including epidermal hydration, ambient temperature, and physical activity. EDA was monitored from 12 subjects during a normal working day. A portable 4 channel cassette recorder (Medilog) was employed to record skin conductance, ambient temperature, and arm movements. The effects of epidermal hydration were assessed using different 0.05 KCl electrolyte media. EDA was quantified throughout the day during several 5-min rest periods and subsequent simple reaction time tasks. In order to distinguish between the influence of time of day and electrode/electrolyte aging, an extra pair of fresh electrodes was applied at each measurement period. Significant effects of temperature, electrolyte medium, and time of measurement on several indices of EDA were obtained. The implications of these data for long-term ambulatory EDA monitoring were discussed.     

Differential Responsiveness of Two Electrodermal Indices to Psychological Stress and Performance of a Complex Cognitive Task

Sixteen high trait anxious and 16 low trait anxious male Ss were assigned to a high stress (HS) or a low stress (LS) condition and were given differentially stressful instructions. All Ss were then required to perform a complex cognitive task, the Halstead Category Test. Adjusted indices of tonic and phasic exosomatic electrodermal activity were monitored throughout the experiment. Level of tonic skin conductance (SC) was only minimally responsive to the manipulation of psychological stress but increased greatly during cognitive and perceptual activity. Phasic activity increased significantly following psychological stress but not following cognitive and perceptual activity. It was concluded that these results support a multiple component theory of electrodermal activity. Phasic electrodermal activity appears to increase with psychological as well as physical threat and was suggested to be a good index of autonomic emotional arousal. Tonic SC appears to change mainly as a function of cognitive activity.     

Comparisons of Sweat Gland Counts, Electrodermal Activity, and Habituation Behavior in Young and Old Groups of Subjects

The present experiment utilized a habituation paradigm to investigate age differences in sweat gland counts (SGC), skin conductance responses (SCR), and skin conductance levels (SCL). The 12 young subjects (mean age 25.3 yrs) and the 12 old subjects (mean age 69.5 yrs) exhibited no reliable age differences in habituation of the SCR or in the magnitude of the SCRs measured. Bilateral conductance recordings revealed no laterality effects for SCR or SCL in either age group. Age differences were found for both SGC and SCL. Correlations of SGC with SCL revealed a strong relationship in the young (r= 74) and a relatively weak correspondence in the elderly (r= .22). The reverse was observed for SGC and SCR correlations, with the old sample showing consistently high correlations and the younger sample consistently low correlations. A stepwise multiple regression analysis showed that the variance in SCL predicted by age was not independent of the variance predicted by differences in SGC. The data are discussed in terms of age-related change in peripheral factors which affect electrodermal behavior.     

A Convenient, Non-hydrating Electrolyte Medium for the Measurement of Electrodermal Activity

Two experiments with 12 subjects each compared electrodermal recordings taken simultaneously with four different electrolyte media. These were polyethylene glycol, Unibase/glycol, Unibase, and hydrated agar (i.e., a site recorded with agar electrolyte after presoaking it with water). The primary purpose was to compare the electrolyte containing a mixture of Unibase/glycol with the other electrolytes. The glycol and the hydrated agar were assumed to reflect low and high levels of epidermal hydration, respectively, while Unibase provided a comparison with Unibase alone. These comparisons were made for positive SPRs and rapid recovery SCRs (and their associated prestimulus levels), which are believed to reflect the endosomatic and exosomatic manifestations of the epidermal membrane response. Unibase/glycol was quite similar to glycol alone; thus it offers a more convenient electrolyte for use when minimal hydration is required. The results were interpreted as indicating that Unibase/glycol is preferable for skin potential recordings, while Unibase is to be preferred for skin conductance recordings.     

Continuous Recordings of Impedance and Phase Angle During Electrodermal Reactions and the Locus of Impedance Change

The relatively few studies that use alternating current (AC) in exosomatic electrodermal recording techniques focus on tonic measurement but not on phasic measures. AC methods of phasic measurement, however, are most useful in testing electrical models of the electrodermal response. Problems arising from AC recording of fast electrodermal changes are discussed, and an appropriate measurement concept for continuous recording of impedance and phase angle is developed. This enables tonic values of both parameters to be offset in order to sufficiently amplify small changes. An AC frequency of 100 Hz was used in recording electrodermal activity in 10 subjects during an habituation series of 80dB 1000 Hz tones. Comparison of transformed curves showed that the main component of electrical changes accompanying electrodermal response is a shift in conductance while susceptance shows only small fluctuations. According to a widely accepted simple electrical model of skin, these results indicate that electrodermal responses take place mainly in the resistive element which parallels the capacitance associated with the stratum corneum, but that other components may be involved too.     

The Effects of Monetary Incentive and Frustrative Nonreward on Heart Rate and Electrodermal Activity

Further investigation of a recent theoretical model positing the existence of mutually antagonistic appetitive versus aversive motivational systems was conducted by providing monetary incentives for 3 trials and then either with or without warning terminating the incentives for the last 2 trials. Two dependent measures-heart rate and electrodermal activity–were employed to test the predictions that incentives would activate the appetitive system and produce heart rate acceleration, while unsignalled termination of incentives (frustrative nonreward) would activate the aversive system and produce relative electrodermal activity increases. An additional goal was to investigate the effects on heart rate of different magnitudes of incentive per response unit and varying the amount of work per response unit–two ways of achieving different total amounts per trial. The data showed a clear and graded heart rate response to varying the amount of work per response unit. These results were interpreted as consistent with the conclusion that the heart rate response is a function of the amount of incentive per unit of effort. In contrast to the clear effect on heart rate, the incentive manipulations had no observable effect on electrodermal activity. Conversely, electrodermal activity showed a clear response to frustrative nonreward, while heart rate was not affected. These results were interpreted as consistent with the notion of separate motivational systems mediating different behavioral effects.     

Lateralization in the Electrodermal System as a Function of Cognitive/Hemispheric Manipulations

Three experiments examined patterns of bilateral differences in skin conductance as a function of cognitive tasks intended to produce specific manipulations in the relative activation of the two hemispheres. Experiments 1 and 2 employed right-handed subjects, and examined the effects of Verbal (left-hemispheric) and Spatial (right-hemispheric) tasks. In both experiments response amplitudes were substantially smaller in the hand contralateral to the more activated hemisphere than in the ipsilateral hand. Experiment 2 also examined the effects of Music and Number tasks, intended to produce a similar level of activation in the two hemispheres: these tasks were not accompanied by reliable bilateral differences in electrodermal activity. Experiment 3 consisted of a replication of Experiment 2 with subjects (sinistrals) known, as a group, to exhibit little functional hemispheric specialization. In these subjects, bilateral electrodermal differences did not vary systematically as a function of tasks. These findings argue strongly for the presence of lateralized cortical influences on electrodermal activity, and their implications for psychological and neurophysiological models of electrodermal functioning are discussed.     

Skin Conductance Recordings and the NaCl Concentration of the Electrolyte

This study examined the effects of four levels of NaCl concentration (0.1–0.7%) on skin conductance responses (SCRs) and levels (SCLs) to deep breaths and loud noise. Twenty-four subjects of both sexes took part in two identical experimental sessions, 7 days apart. All subjects encountered all four electrolyte concentrations. The results showed no effects of electrolyte concentration on SCLs or on the SCRs to the deep breaths, but indicated larger SCRs to the loud noise with the highest NaCl concentration.