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PSY9UA4/PSYPCO2 Laboratory Session 1 Introduction to Electrodermal Activity (EDA)

PSY9UA4/PSYPCO2 Laboratory Session 1 Introduction to Electrodermal Activity (EDA) Introduction As you may recall from class, the nervous system can be divided into two main divisions, the central nervous system and the peripheral nervous system. One part of the peripheral nervous system is the autonomic nervous system, and it is comprised of nerves that modulate the activity of many of our organs. The goal of today’s lab is to learn how to record changes in the body that are due to the activity of the autonomic nervous system. The two measures that we’ll record today are heart rate (HR) and electrodermal activity (EDA). The EDA is essentially a measure of the change in sweat gland responses, typically measured in the hand, in response to the presentation of a stimulus. Changes in both heart rate and EDA are modulated by the autonomic nervous system. EDA is also sometimes referred to as the galvanic skin response (GSR). The equipment in this laboratory session is a computerised version of the conventional polygraph. EDA activity will be recorded using electrodes placed on the non-dominant hand and heart rate using electrodes placed on each wrist. These electrodes will measure changes in the electrical signal produced by the heart (for the heart rate), and changes in how conductive the skin is (for the EDA). A computer will display the two sets of signals as ongoing traces. In this lab you’ll get a chance to record the EDA and HR from your classmates, and have the opportunity to have them recorded from yourself. To elicit a change in EDA and HR, you will be provided with some everyday stimuli with which you can try to elicit a response from the person being recorded from. Background readings on the physiological basis of the EDA are available in the module handout which is uploaded on the PSYU9A4 Canvas page. Procedure The class will be divided into sub-group of about five members. Each member can have the opportunity to participate but this is voluntary. Using the `Biopac` system, open Lesson 9: polygraph. 1. Give a name to the data file that will hold your data [i.e. mondgp4Anna]. You won’t need this, but the program asks for it. 2. For the EDA, the rectangular stickers (electrodes) should be used. One sticker should be attached to the index finger on the nondominant hand of the volunteer, and the other should be attached to the finger next to this on the same hand. 3. For the heart rate, use the circular stickers (electrodes). Attach one sticker to the inner surface of each wrist. 4. To connect the electrodes to the blue recording machine (the Bio Pac), you’ll use the two sets of wires coming from the machine. For the EDA, connect each sticker on the finger to one wire of the cable with two wires coming from it (one red, one black). It doesn’t matter which way around these wires are connected to the stickers. For the heart rate, use the red and white wires of the cable with three wires coming out of it. Connect the red wire to one wrist electrode, and the white wire to the other wrist electrode. Again, it doesn’t matter which way around these go. The black wire isn’t used. 5. The first stage in obtaining the EDA and HR is to calibrate the machine. Basically, different people have different EDA levels, so the machine set its sensitivity accordingly. To calibrate the machine, one of the experimenters should press the “calibrate” button. Ignore the error message, and hit yes or ok to the question asking about whether the subject is relaxed. Next you’ll see a trace on the screen. After a few seconds there will be a little beep, and the volunteer should take a deep breath and then exhale sharply. That’s it for calibration. 6. Begin recording, again ignoring the error message. Wait five seconds and then ask your participant to relax (approx 20 seconds). Mark the onset of the relaxation period by pressing F9. 7. Whilst the polygraph is still running administer the chosen condition, remembering to event mark this by pressing F9 on the computer. 8. Once the EDA has levelled out, once again ask your participant to relax, and press F9 (for at least ten seconds). 9. Click on suspend. 10. Click on `Done` to finish recording. Then choose `analyse current data file`. 11.The respiration data isn’t needed, and if you press “altl” and click on the red ‘40’ button it will go away. There are several different measures we can get from this recording. Here we’ll focus on two, the mean and the change from peak-to-peak (PP). The mean is the average value across the time period that you’ve selected. The P-P is the change from the highest to the lowest value over the time period you’ve selected. 12. To get the data, there are three buttons near the top of the screen to pay attention to. The first will have a number, like “41”. This is the channel that you are recording (EDA or HR). The second is “value”, and this is what you want to measure. If you click on this, you can choose mean, P-P, or other things. The third space is where the values of whatever you choose will be displayed. This is what you want to record below. 13.First, select the EDA channel, and the “delta-T” option in the value list. Then take the I-beam tool at the bottom of the screen, and drag it over a 10-second period after the F9 arrow. The delta-T option just tells you how long of a period of time that you’ve selected. 14.Choose the EDA channel again, and select the mean and the P-P. Do the same for the heart rate channel. You now have the values for heart rate and EDA for the 10 second period after the person began relaxing. Obtain the same values for the 10-15 second period following presentation of the stimulus, and following the final 10-15 second relaxation period. 15.Data should be rounded to 2 decimal places. 16.Select another participant and re-run the experiment choosing a different condition. It’s helpful to note which person in your group has a particularly clear EDA, as they may be good candidates for being the volunteer in Lab 2


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