While the term “GSR” is regularly used among laypeople, the purpose of this section is to prepare you to compete in a science fair, and for that reason, the more current and scientifically precise expression “electrodermal response” (EDR) will be used here. If you are unfamiliar with this technology, it is recommended that you read this page before moving on to the science fair projects. For those who already have a pretty good understanding of what this technology does, you can click on any of the projects on the left. (Note: the list of pages grows continually as new projects are added). These projects are suitable for grades 6 through 12 or even college level, depending on the complexity the student builds into the experiment.
Background: What is the Electrodermal Response?
The electrodermal response (EDR) is a method for detecting physiological arousal in a most direct manner, even when the person denies it or is unaware of it. It is accomplished by the use of sensors that are placed on the skin which are sensitive to changes in the skin’s electrical properties. Investigation of the electrodermal phenomenon has gone on for more than 100 years, and it is a convenient method to explore processes in human learning, conditioning, perception, even deception.
How are EDRs detected?
When the sweat pores open, an amount of moisture is moved from inside the body to the surface of the skin. This is happening almost constantly, from moment to moment, though it is usually not sensed by the person except if there were suddenly a lot of moisture on the hands. If a very small electrical current is passed over this area of the skin, the electricity will move more easily when the skin is wet than when it is dry. EDR circuits are built to detect the changes in how easily the current moves between two points on the skin. EDRs last from a few seconds to up to a minute or more. Most people have hundreds, even thousands of EDRs in a day, though they are not aware of them. Only with a simple electrical circuit can they be detected.
Are electrodermal devices safe?
The amount of electricity needed to detect EDR is very, very small, far less than would be experienced if you were to hold an AAA size battery by the two terminals with your hand.
Terms, Concepts and Questions to Start Background Research
To do some of the science fair projects you it is helpful to understand and be able to explain the following terms and concepts:
* Electrodermal response (EDR) * Concealed Information Test (CIT) * Keys (sometimes called “critical items” in some CIT research) * Probability * Skin conductance (SC) * Skin resistance (SR) * Autonomic Nervous System (ANS) * Sympathetic Nervous System (SNS) * Peripheral Nervous System (PNS) * False positive, false negative, true positive and true negative * Biographic information * Episodic memory * Orienting response * Habituation * Conditioning
If you think you now have a good understanding of the EDR, take a look at any of the science fair ideas listed on the tabs to the right. If you would like a little more practical experience, try running a Concealed Information Test (CIT).
The premise of the CIT is that when someone is presented with several stimuli, among which is a stimulus that carries a unique significance to him or her, there will be a larger electrodermal response to the stimulus with the significance than to the other stimuli. This effect is quite reliable. In lie detection, tests are constructed in which the significant items are those that only a guilty person would know and they are embedded among other items that sound plausible but do not relate to the crime under investigation. When the tests are administered, innocent persons react randomly to all of the items, but the guilty person, who knows which items relate to the crime he committed, reacts greatest to the guilty items (often called “keys” by polygraph examiners).
Standard Concealed Information Test
Preparation
1. The examiner must prepare the question lists in advance. There can be no surprise questions during the testing (EDRs can be produced by surprise, confusion, and poor test practices.)
2. There should be at least three lists of items, though the number can go as high as desired.
3. Each list should have 6 items, with only one of them being a key.
4. The key is placed in the list randomly, except it cannot occupy the first position.
5. Seat the examinee in the test chair and place the sensors on two fingers of the examinee’s hand.
6. Face the examinee toward a blank wall in such a way as not to be able to see the examiner. See Figure 1.
7. Before testing begins the examiner should tell the examinee what the test is about without revealing what the key for each test is.
a. Explain that there will be several tests. b. Explain that the examinee must remain still during the test, face forward, and follow instructions. c. Explain that the examinee must follow directions. Failure to do so will require starting the testing over from the beginning. d. Tell the examinee all of the items that will be used in the tests, but not in the order they will be presented during the tests.
Figure 1. Below is an overhead depiction of a possible configuration of the test area. “A” denotes the seat of the CIT examiner, and “B” is where the examinee is placed.
Testing
1. Turn on the electrodermal recorder, and wait for the signal to stabilize.
2. Be sure to make no distracting noises or movements.
3. Start the first CIT by saying something like: I will now test you regarding X (e.g., that item that was “stolen”). After I say each item, repeat it back to me.
4. The items are presented about 15 seconds apart.
5. Each CIT is given only one time.
6. Repeat this procedure for each of the CITs.
Analysis of the EDRs
1. It is likely that every item on each test will cause a reaction, especially the first item on each list. This is normal and expected.
2. Begin scoring the first CIT. Ignore the reaction to the very first test item.
3. If the largest reaction occurred at the key, that test is scored as a 2.
4. If the second largest reaction occurred at the key, the test is scored as a 1.
5. Otherwise, the test is scored as 0.
6. Repeat these steps with every CIT.
7. Add all of the scores together for all of the CITs.
8. The maximum possible score will be two times the number of CITs, and the minimum possible score will be zero.
9. If the total score is equal to or greater than the number of CITs, the examinee has failed the test.
10. If the total score is less than the number of CITs, the examinee has passed the test.
Scoring Practice
Figure 2. Typical EDR waveform.
Figure 2 above is an example of a recording of electrodermal reactions. It is read from left to right. When the tracing moves upwards, it is an indication of a reaction. The letters at the bottom of the tracings represent where the examiner said something to the examinee, and they are about 20 seconds apart. The “X” is where the examinee was told that the test was beginning. The letters “A” through “F” are where the six CIT items were presented. Note that the examinee has reacted to every item, which is typical.
Using the Lykken Scoring System, you assign a score to the CIT based on where the largest reaction took place. Remember not to consider the announcement of the start of the test (at “X”) or the reaction to the first item (at “A”). In the chart above only items “B” through “F” would be considered. If, in this example, the key had been item “B”, the test would have received a score of 2. However, if the key had been item “C”, the test would have been scored as 1. If the key had been items “D,” “E”, or “F” the test would have been scored as 0.
Because the key is randomly placed for each CIT, it is probable that its placement will change from test to test.
To make a decision as to whether the person is concealing information, you must add up the scores and compare the score to the number of CITs. For example, if there were 4 CITs, a total score of 4 or more would indicate that the person had the concealed information. Scores of 3 or lower would indicate that the examinee did not recognize the keys. If there were 7 CITs, a score of 7 would be the threshold for failing the test, if 9 CITs, a score of 9, and so on.
