The skin conductance response, also known as the electrodermal response (and in older terminology as "galvanic skin response"), is the phenomenon that the. Electrodermal activity (EDA) is the property of the human body that causes continuous variation in the electrical characteristics of the skin. Historically, EDA has also been known as skin conductance, galvanic skin. Skin conductance (SC) is normally measured with 8mm diameter silver/silver chloride electrodes positioned on the medial phalanx of the index and middle.
Galvanic skin potential GSP refers to the voltage measured between two electrodes without any externally applied current. It is measured by connecting the electrodes to a voltage amplifier. This voltage also varies with the emotional state of the subject.
A painful stimulus such as a pinprick elicits a sympathetic response by the sweat glands, increasing secretion. Although this increase is generally very small, sweat contains water and electrolytes, which increase electrical conductivity, thus lowering the electrical resistance of the skin. These changes in turn affect GSR. Another common manifestation is the vasodilation dilation of blood vessels in the face, referred to as blushing, as well as increased sweating that occurs when one is embarrassed.
EDA is highly responsive to emotions in some people. Fear, anger, startled response, orienting response, and sexual feelings are among the reactions that may be reflected in EDA. These responses are utilized as part of the polygraph or lie detector test. EDA in regular subjects differs according to feelings of being treated fairly or unfairly, but psychopaths have been shown to manifest no such differences.
EDA is a common measure of autonomic nervous system activity, with a long history of being used in psychological research. Critchley, Chair of Psychiatry at the Brighton and Sussex Medical School states, "EDA is a sensitive psychophysiological index of changes in autonomic sympathetic arousal that are integrated with emotional and cognitive states.
Oftentimes, EDA monitoring is combined with the recording of heart rate, respiratory rate, and blood pressure, because they are all autonomically dependent variables. EDA measurement is one component of modern polygraph devices, which are often used as lie detectors. The E-meter used by the Church of Scientology as part of its practice of " auditing " and " security checking ", is a custom EDA measurement device. External factors such as temperature and humidity affect EDA measurements, which can lead to inconsistent results.
Internal factors such as medications and hydration can also change EDA measurements, demonstrating inconsistency with the same stimulus level. Also, the classic understanding has treated EDA as if it represented one homogeneous change in arousal across the body, but in fact different locations of its measurement can lead to different responses; for example, the responses on the left and right wrists are driven by different regions of the brain, providing multiple sources of arousal; thus, the EDA measured in different places on the body varies not only with different sweat gland density but also with different underlying sources of arousal.
These show the complexity of determining the relationship between EDA and sympathetic activity. From Wikipedia, the free encyclopedia. Retrieved 20 October What Happens in the Brain". Retrieved 15 April The College of Information Sciences and Technology. Retrieved 20 April Retrieved 16 April Retrieved 28 February Gianfranco Denes, Luigi Pizzamiglio. Monkey faces were chosen from a large library which categorized the images along the dimensions of monkey identity, direction of gaze averted or direct , and facial expression appeasing, neutral, or threatening Gothard et al.
A stimulus set consisted of 10—24 images, presented in pseudorandom succession within 10—30 repeated trial blocks. Each monkey was seated in a dimly lit room and allowed to drift in and out of sleep.
The duration of this time period was not fixed, but a typical session would last 30 min. Two states within the rest condition were also identified: The onset of SCRs was detected using a custom-designed Matlab script to identify positive deflections in the first derivative of smoothed electrodermal activity ms moving average.
SCRs were user verified in accordance with the canonical waveform described by Edelberg SCRs occurring 1—3 s after image onset were attributed to the image on the basis that the minimum latency of an SCR that could be elicited by an unexpected loud tone was 1. During the image viewing task, the probability of an SCR occurring at each of 30 time bins of ms each, spanning the time course of trial events, was calculated for both monkeys.
Spearman's rank correlation was used to determine if either the probability of images eliciting SCRs within a block or the magnitude of evoked SCRs indicated habituation of either measure. Within the rest period, perievent time histograms of SCR occurrences were constructed using 1-s time bins spanning a s window centered at the opening and closing of the eyes.
The raw spike trains were converted to continuous firing rates using the spike count observed in a 1-s moving window translated across the spike train with a 1-ms step size. SCR-triggered averages were computed for each unit within a s time window centered at the onset of SCRs. Each SCR-triggered average was normalized to its own baseline activity by subtracting the mean of the entire trace from the value of each time point along the trace.
Additionally, for each individual SCR-triggered firing rate average, the largest deviation from baseline that occurred in the 2 s period prior to SCR onset expressed as a z-score was computed. The mean and median change in firing rate was calculated at each time point across the population of mean-corrected SCR-triggered averages. The resulting population trace was then expressed in units of SDs away from its own mean z -score. This was computed to determine if the net change from baseline firing activity observed across the population was significantly different near the onset of SCRs than at any other time.
The procedure was also carried out after mean-corrected SCR-triggered averages had been converted to absolute values, as this would allow evaluation based only on the absolute magnitude of deviation from baseline.
Finally, the raw spike train of each unit was used to create a peri-SCR time histogram with ms bins spanning a s window.
The locations of the significant bins were then recorded for each unit and combined into summary histograms Fig. Neural activity centered on SCR onset in different experimental conditions. SCR-triggered firing rate averages were calculated for each unit and normalized to their baseline firing rates.
At each time point, the population mean black trace and median gray trace were calculated. This convention is carried over into C. The horizontal dotted lines indicate a z -score value of 3. The traces in C were calculated as in B except that each normalized SCR-triggered average was first converted to changes in the absolute value of the firing rate.
When only response magnitude is considered A and C , clear SCR-related activity is evident in both experimental conditions. The effects are cancelled out when direction is considered as well B.
Monkey T viewed 14 image sets 3, image presentations , and monkey H viewed 9 image sets 1, image presentations. Figure 2 A shows the probability of SCR occurrence in both monkeys as a function of trial progress. Because the minimum latency for an SCR is 1 s, the SCRs produced by monkey T can be attributed to the images or anticipation of reward, whereas in monkey H , the SCRs were triggered by anticipation of stimulus images or reward delivery from the previous trial.
Probability of SCR occurrence across all sessions as a function of trial progress during the image viewing task. Histograms of SCR occurrence in monkeys H and T top and bottom , respectively centered on the closing and opening of the eyes. The average time spent in each rest session with eyes open and closed were The change in SCR frequency between the two states was time locked to the opening and closing of the eyes Fig.
During the period of rest, single units were recorded from the amygdala 48 from monkey H , 56 from monkey T and during image viewing, a different set of single units were recorded and 47 units from monkeys H and T , respectively. The number of single units recorded from each nucleus and their respective average firing rates are presented in Supplementary Table S2. More units exhibited significant modulations in neural activity during the 2 s preceding SCR onset than any other time over the course of a s time window Fig.
Each ms time bin in Fig. At the population level, no clear net increase or decrease of firing rate was observed surrounding the onset of SCRs Fig. This might reflect the cancellation of responses that occurred in positive and negative directions with regard to baseline activity e. When only the magnitude of deviation from baseline activity is considered, a significant increase in the population's mean and median deviation from baseline emerges during the 2 s before SCR onset Fig. The response distribution across the population of single units was bimodal and approximately symmetric Fig.
Recordings from the basolateral lateral, basal, and accessory basal nuclei and centromedial central and medial nucleus, as well as the anterior amygdaloid area nuclei had similar response distributions within both conditions image viewing: Distribution of SCR-related firing rate modulations across the population of single units for both experimental conditions.
Single units are evenly split between those that show positive and negative changes in firing rate. The magnitudes of these responses are comparable, suggesting 2 distinct populations of units.
During the rest period, the probability of SCR occurrence was modulated by the opening and closing of the eyes Fig. When SCRs that occurred within 10 s of the eyes opening or closing were removed from the analysis, SCR-related activity was still clearly present Fig. SCR-related neural activity is not dominated by the opening and closing of the eyes. Although this technique had the effect of decreasing the number of highly modulated units compare A with Fig. The results presented here indicate that neural activity in the amygdala marks the occurrence of an SCR regardless of its immediate trigger.
In the context of a passive image viewing task, SCRs can occur spontaneously or be triggered by task-related factors. Given the variety of causative factors, the occurrence of an SCR cannot be used as an independent and reliable measure of stimulus image content, at least under these experimental conditions. Even so, the amplitudes of image-evoked SCRs do seem to be useful in determining which categories of images are on average more arousing.
Within the rest condition, a fraction of the observed SCRs were related to the opening of the eyes, yet SCR-related activity was independent of this trigger, and the remaining SCRs could not be attributed to any tractable event.
SCR-related changes in firing rate had a bimodal distribution regardless of the nucleus from which each unit was recorded. A similar bimodal distribution of response types was reported by Pascoe and Kapp in the central nucleus of the rabbit amygdala in conjunction with conditioned heart rate deceleration.
The presence of neurons that either increase or decrease their firing rates in relation to the same autonomic output suggest that multiple pathways transmit signals from the amygdala to the autonomic centers of the brain stem. The SCR-related activity observed in various nuclei of the amygdala may have different functional consequences.
The centromedial nuclei are reciprocally connected to the autonomic centers of the brain stem and hypothalamus Price and Amaral and could directly influence the generation of SCRs. Rise Time seconds — Time interval between the start trough of the response and the maximum amplitude peak. The half recovery point is not always present, especially if a second SCR begins before conductance levels have dropped sufficiently. SCRs are identified in the EDA Analysis application in alternating colors to distinguish subsequent responses from one another.
Statistics related to the identified SCRs are found in the table to the right and below. Tonic skin conductance refers to the rest of the signal, i. This can give a good approximation of baseline EDA for a given segment of data.
Changes in Tonic SCL over time can be indicative of more general fluctuations in arousal. It can be a useful indicator of overall activity in a given time period, where a higher Tonic Period corresponds to a reduced activity level.
Depending on the type of study being run, there is a case for using each of the variables discussed above. There are a couple of ways to perform this average, and it is highly debated which method is superior. It is, however, important to understand the difference between each of these methods. In many cases, it may be best to simply report both.
Amplitude and magnitude are not statistics directly reported by the EDA application, but can easily be calculated from the output file.
Jul 17, Skin conductance is not under conscious control. Instead, it is modulated autonomously by sympathetic activity which drives aspects of human. Skin conductance (SC) has a simple curve form always with an initial rapid increase and a slower recovery. SP curves are more complicated. Many papers, such. The skin conductance response (SCR) is an indirect measure of sympathetic autonomic activity that is associated with both emotion and attention. In humans.