The galvanic skin response is an electrodermal response that detects the change in conductivity of a person’s skin after perspiration. A greater amount of sweat is produced when a person becomes uncomfortable or nervous in any given situation (Gruber & Moore 1997). Sweat glands are located all over the body, however, there are about ten times as many glands located on the surfaces of the palms and the soles of feet, making these volar surfaces great for detection. Skin conductance is broken into two categories: tonic skin conductance and phasic skin conductance. Tonic skin conductance is a general baseline that differs from person to person. Phasic skin conductance changes when something occurs. Environmental changes can cause a change in the skin conductance which will eventually return to a baseline level within a few seconds (Lab Handout). These are measured by placing electrodes on the tips of two fingers. An amplifier creates a constant voltage through the skin. When the sweat glands fill with sweat, their conductance increases (Villarejo, et al. 2012). This change in conductance can be measured and displayed in a graphical form. The purpose of this experiment was to determine if the galvanic skin response is an appropriate means of detecting nervousness or deception in someone. Sweating is a physiological response that aids in thermoregulation. It also plays a role in the acute stress response or “fight or flight” response. This response occurs during stressful situations, like when a person becomes nervous or uncomfortable. During this response, the adrenal glands release catecholamine hormones, like epinephrine. This release of epinephrine causes activation of the sweat glands resulting in higher sweat production (McCorry 2007). Based on this idea, the galvanic skin response should be a viable way to detect nervousness or deception in a given individual.
Materials and Methods
- Mac Computer
- IXTA, USB cable for connection to computer, IXTA power supply
- iWire-B3G GSR amplifier
- GSR electrodes
The equipment was set up by connecting the IXTA to the computer via a provided USB cable, and also connecting it to a power outlet with the power supply cable. The iWire-B3G GSR amplifier was connected to the IXTA. GSR electrodes were connected to the amplifier. The GSR unit was precalibrated and no other calibration was required. The lab consisted of three exercises. For exercise one, all four group members were measured. For exercises two and three, only one group member was measured. For each exercise, all subjects washed their hands prior to be connected to the GSR electrodes. This removes all surface oils that could interfere with the skin conductance reading. Finger tips were left slightly damp for all subjects to allow for better skin conductance. The electrodes were placed on the index finger and ringer finger of the right hand on all subjects. Subjects were asked to sit calmly facing away from the monitor, with the electrodes resting on something sturdy. All other members of the group were asked to remain quiet and still as to not interfere with the readings.
This exercise performed a tonic skin conductance level base line and a habituation baseline. For the tonic skin conductance reading, the subject was connected to the electrodes and one other group member started a recording for at least one minute. After the one minute mark, the habituation measurement began. A separate group member began asking the subject the question: “Is your name…?” Each time the subject was to respond “Yes.” After the response from the subject, the tonic skin conductance level would drift away from the baseline and then eventually return back within a few seconds. The member at the computer would set marks after the tonic skin conductance level returned to the baseline. This continued until the tonic skin conductance level did not drift away from the baseline once the question was asked. Data was collected and analyzed. This was done for all four members of the group.
For this exercise, the subject was asked a serious of neutral content questions such as: “Do you live in a dormitory?” and “Are you a senior?” The subject was asked a total of ten questions of this manner. The questions were asked in a random order, so that the subject wouldn’t know what would be asked. The reading was performed in the same manner as exercise one. Data was collected and analyzed. Only one subject was measured for this exercise.
For this exercise, the subject was asked both neutral content questions similar to questions in exercise two, as well as emotional content questions such as: “Are you in love?” and “Do you ever hide some of your feelings?” Again a total of ten questions was asked in a random order. Seven neutral content questions were asked, and three emotional content questions were asked. The reading was performed in the same manner as exercises one and two. Data was collected and analyzed. Only one subject was measured for this exercise.
Figure 1: Table shows result from exercise 1. Subject number, followed by average skin conductance level over a 1 minute time period measured in µSiemans, followed by spontaneous skin responses measured over a one minute time period, and habituation score.
Figure 2: Table shows results from exercise 2. Subject was asked ten neutral content questions. The baseline, peak response, and change in the two were recorded in µSiemans, as well as peak response time recorded in seconds.
Figure 3: Table shows results from exercise 3. Subject was asked seven neutral content questions (NC) and three emotional content questions (EC). The baseline, peak response, and change in the two were recorded in µSiemans, as well as peak response time recorded in seconds.
Graph 1: Shows average times for both neutral (blue) and emotional (red) content questions in seconds.
Neutral Average: 5 secs.
Emotional Average: 7.31 secs.
Graph 2: Shows average change in skin conductances for both neutral (blue) and emotional (red) content questions in seconds.
Neutral Average: -0.284µS
Emotional Average: -0.22 µS
As stated earlier, Figure 1 shows the baseline reading for each of the four group members. The table shows that there wasn’t a lot of variation in the baseline measurement between group members, with the exception of subject 3, whose baseline was slightly higher than the other three members of the group. The habituation score seems to be similar in all four group members as well.
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Figure 2 shows the readings for one subject in exercise two, where only neutral content questions were asked. Note that subject 1 from exercise one is used in the following two exercises. According to the table, it seems that the subject had only slight changes in the baseline readings as well as the peak response. The average baseline reading in exercise two was 248.055µS. This is a slight drop from the original baseline. The average peak response w.as 247.915µS. The average change in skin conductance was -0.1395µS. The time doesn’t vary much either. The average rise time was 7.994 seconds. It is possible that the subject was just having a normal day, and was prepared to be tested. Also, these were all neutral content questions that the subject should have had no reason to feel uncomfortable answering.
Figure 3 shows both emotional and content questions. Again, none of the columns seem to vary too much. The average baseline was 255.622µS, this is a slight increase from the previous baseline. However, it is not a large enough change to be considered significant. The average peak response was 255.393µS.
Graphs 1 and 2 both compare value obtained from exercise three. The first graph compares the average in peak response rise time for neutral content questions (shown in blue) and emotional content questions (shown in red). It seems that there was a 2.31 second change in rise time between the two. This is indicative that it took the subject slightly longer to answer these questions, which shows that the subject was slightly uncomfortable. However, looking at the times from figure three, there is a 4.29 second increase from the first neutral content question to the first emotional content question. This shows that the subject became somewhat uncomfortable when asked, and hesitated to answer. As questions progress, the time begins to decrease back to normal, showing that the subject acclimated to what questions were being asked. Graph 2 shows the change in skin conductance between neutral content questions (shown in blue) and emotional content questions (shown in red). The average change in skin conductance for neutral content was -0.284µS, and for emotional content, the average was -0.22µS. This is only a slight change, and is not significant enough to gather information. However, this is somewhat contradictory to the time data gathered that was previously discussed. It is possible that the first emotional question didn’t make the subject uncomfortable, but it did catch the subject off guard. This would explain the time increase with only a slight change in skin conductance.
In theory, galvanic skin response should be a viable way to determine if someone is deceitful or nervous in some situation. However, according to the data collected, it isn’t exactly true. The galvanic skin response is probably viable for someone completely unprepared and asked extremely personal content in which a lie would matter. For this lab, the subject was very calm. All group members known the subject, so the subject likely felt comfortable being asked personal questions by the group. Whereas in a more strict setting, the subject probably wouldn’t know the examiner, and would feel more nervous about being asked intense questions.
It is also important to note that there was some error that occurred in the exercises, as with any lab experiment. The iWorx software was new to all group members, and the data could have possibly been interpreted incorrectly resulting in false results. There could also have been issues with the electrodes or the moistness of the subject’s fingertips. There could have also been flaws in the way questions were asked. There was plenty of room for user error in the experiment.
Overall, the idea was to show that the galvanic skin response is a viable technique. Depending on the reader’s interpretation, this may or may not be true. The change in time shows some nervousness, but the change in skin conductance does not. However, the emotional questions could have just caught the subject off guard which could have resulted in an increased response time.
In order to obtain a more precise answer, the experiment should be ran again after the users have had more experience with the software and the electrodes, as well as with data analysis. Ideally, more emotional content questions would be asked, and more subjects would have been tested. This could possibly give a more definite “Yes, this method is viable.” Or “No, this method is not viable.”
- Gruber M, Moore P. “Galvanic Skin Response.” The Science Teacher. 1997. 64(9)
- No Author, “Experiment HP-2: The Galvanic Skin Response (GSR) and Emotion.” Lab Handout.
- Villarejo M, Zapirain B, Zorrilla A. “A Stress Sensor Based on Galvanic Skin Response (GSR) Controlled by ZigBee.” Sensors. 2012. 12(5).
- McCorry, Laurie Kelly. “Physiology of the Autonomic Nervous System.” American Journal of Pharmaceutical Education. 2007. 71(4).
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