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Measuring Emotional
Responses to the
Acoustic Startle Reflex:
Stimulus Habituation &
Sensitization
BIOPAC Student Lesson
GALVANIC SKIN RESPONSE
& THE POLYGRAPH
Revised 3/23/
D. W. Pittman, Ph.D.
Wofford College
Modified from:
Richard Pflanzer, Ph.D.
Associate Professor Indiana University School of Medicine Purdue University School of Science
William McMullen
Vice President BIOPAC Systems, Inc.
BIOPAC Systems, Inc.
42 Aero Camino, Goleta, CA 93117 (805) 685-0066, Fax (805) 685- Email: info@biopac.com Web Site: http://www.biopac.com
BIOPAC Systems, Inc.
I. INTRODUCTION
Electricity flows through an electrical circuit because of a difference in electrical pressure between the beginning and the end of a circuit. Electrical pressure or electromotive force (E) is measured in volts (V). The flow of electricity, called current (I), is measured in amperes (A) or amps for short. As electricity flows through the circuit, resistance to flow occurs. Electrical resistance (R) is measured in ohms (Ω).
In a simple circuit of direct electrical current, the relationship between the electromotive force causing the electrical current, the resistance to flow of electricity, and the resultant magnitude of the current is described by Ohm’s Law.
Ohm’s Law : I (Amps) = E (Volts) / R (Ohms)
If two of the three variables are known, the unknown third variable can be calculated.
For example , if voltage and resistance values for a simple circuit are known, the above formula can be used to calculate the value for current; if the values for current and resistance are known, then the formula for computing voltage is E = IR.
Ohm’s Law implies that if a constant current is applied across a resistance, changes in the resistance will produce a voltage change directly proportional to the resistance change.
For example , if a constant current of 1.0 ampere is applied across a resistance of 2.0 ohms, the measured voltage would be 2.0 volts (I = E/R, 1.0 ampere = 2.0 volts/2.0 ohms). If the resistance dropped to 0.5 ohm, the voltage would also fall to 0.5 volt (I = E/R, 1.0 amperes = 0.5 volt/0.5 ohm).
In this lesson, you will apply principles of Ohm’s Law and record changes in the electrical resistance of the skin.
The human skin displays several forms of bioelectric phenomena, especially in areas of the extremities such as the fingers, palms of the hands, and soles of the feet. ¾ Galvanic skin resistance (GSR) — When a feeble electric current is steadily applied between two electrodes placed about an inch apart, the recorded electrical resistance between them, referred to as the galvanic skin resistance (GSR), varies in accordance with the emotional state of the subject. ¾ Galvanic skin potential (GSP ) — Similarly, if the electrodes are connected to a suitable voltage amplifier, but without any externally applied current, the voltage measured between them, referred to as the galvanic skin potential (GSP), varies with the emotional state of the subject. The combined changes in the GSR and GSP related to the emotion of the subject constitute the galvanic skin response.
The physiological basis of the galvanic skin response is a change in autonomic tone, largely sympathetic , occurring in the skin and subcutaneous tissue in response to a change in the affective state of the subject. Changes in peripheral autonomic tone alter sweating and cutaneous blood flow, which in turn change GSR and GSP.
For example , if a painful stimulus such as a pinprick is applied to the skin in an area distant to the electrode, the stimulus will reflexively elicit a general phasic sympathetic discharge to sweat glands,
IV. EXPERIMENTAL METHODS
For further explanation, use the online support options under the Help Menu.
A. SET UP
FAST TRACK Set Up DETAILED EXPLANATION OF S ET UP S TEPS
- You will use the NEURO8 computer to record your data and the NEURO computer for the stimulus delivery.
The log-in for both NEURO8 and NEURO10 is PSYNEURO password: Psychology
- Make sure the BIOPAC MP30 unit is turned OFF.
- Plug the transducers in as follows:
Respiration (SS5LB) — CH 1 Electrode lead set (SS2L) — CH 2 GSR (SS3LA or SS57L) — CH 3
BIOPAC MP35 or MP
Respiratory Transducer (SS5LB or SS5LA or SS5L) plugs into CHannel 1
Electrode lead set(SS2L) plugs into CHannel 2
GSR (SS3LA – shown or SS57L lead) plugs into CHannel 3
Fig. 9.1 Equipment Connections
4. Turn the MP30 Data Acquisition Unit ON.
- Attach the respiratory transducer (SS5LB) to the Subject (Fig. 9.2).
IMPORTANT
If using the SS5LA transducer, you must be very careful to not pull or yank on the rubber bow tie portion that contains the sensor element.
Set up continues…
Attach the respiratory transducer around the chest below the armpits and above the nipples (Fig. 9.2). The correct tension is critical. The respiratory transducer must be slightly tight at the point of maximal expiration. The respiration transducer can be applied over thin clothing, such as a t-shirt.
Fig. 9.2 SS5LB Placement
- Setup the GSR. HINT For a good signal to be picked up, it helps if the subjects have a little sweat on their hands (not a lot, but enough so that their hands are not completely smooth or cold). If subjects wash their hands just prior to the recording or if they have been sitting in a cold room, then they must do something to activate the sweat glands before beginning calibration or recording. If subjects begin with colder hands, the scale will be diminished and the signal will be easily saturated once they “warm up” during the lesson.
SS3LA and GEL
Fill both cavities of the GSR transducer (SS3L/SS3LA) with gel and attach to the Subject (Fig. 9.4).
IMPORTANT You must fill both sensor cavities with electrode gel (GEL1) before attaching to the fingers.
Set up continues…
You must fill the each cavity of the SS3L/SS3LA GSR transducer with electrode gel to obtain accurate recordings. The SS3L and SS3LA attach to the fingertips in an identical manner (Fig. 9.4) and should be in place for at least five minutes prior to the start of recording.
Sensors attach to bottom of fingertips
Velcro straps wrap around fingers
Fig. 9.4 SS3L/SS3LA attachment and connection The SS3L/SS3LA is typically placed on the index and middle finger of the left hand. Position the transducer so that the sensor is on the bottom of your fingertip (the part without the fingernail) and wrap the Velcro^ tape around the finger so the transducer fits snugly but not so tight that blood circulation is cut off. It’s a fine line between tight and too tight.
B. CALIBRATION
The Calibration procedure establishes the hardware’s internal parameters (such as gain, offset, and scaling) and is critical for optimum performance. Pay close attention to the Calibration procedure.
FAST TRACK Calibration DETAILED EXPLANATION OF CALIBRATION S TEPS
- Seat the Subject facing the Director and away from screen. Fig. 9.7 MISSING The Subject should be lying on their back on the bed in a relaxed, comfortable position. The arms should be at their sides with the palm and fingers placed face down on the bed and their legs should be straight. The subject should be wearing the headphones and the blindfold.
- Click Calibrate. The Calibrate button is in the upper left corner of the screen.
- Three seconds into the recording, a beep will sound and Subject should inhale and exhale deeply for one cycle, then return to normal breathing.
The program needs to see a change in the GSR recording during calibration.
- Wait for the Calibration to stop. The Calibration will run for 10 seconds and then stop automatically, so let it run its course.
- Check your calibration data. At the end of the 10-sec calibration recording, your screen should resemble Fig. 9.8.
Figure 9.8 Sample Calibration Data ¾ If similar, proceed to the Data Recording section.
All three recording channels should show some fluctuation. There should be some variation 4-6 seconds into the GSR recording from the deep inhale. ¾ If different, Redo Calibration.
END OF CALIBRATION
If a channel does not show fluctuation, the transducer may not be connected properly or the Subject may not have inhaled deeply enough. IT IS EXTREMELY IMPORTANT THAT YOU CAN SEE SMOOTH MOVEMENT OF THE RESPIRATION CHANNEL (red line) & THAT YOU CAN SEE THE GSR (green line) DURING THE ENTIRE CALIBRATION. IF NOT, THEN REDO THE CALIBRATION AND ADJUST THE RESPIRATION BELT. Click Redo Calibration and repeat the entire calibration sequence until your data resembles the sample data.
C. RECORDING LESSON DATA
FAST TRACK Recording DETAILED EXPLANATION OF RECORDING S TEPS
- Prepare for the recording. Hints for obtaining optimal data:
a) The Subject must stay alert, quiet, motionless, but NOT FALL ASLEEP during the 10 minute test. b) The environment must be quiet. c) Sensory input besides the recording must be kept at a minimum since almost any change in the environment may evoke a response. d) Subject should be at his/her resting heart rate in a relaxed mental and physical state, and should not have performed any recent physical or mental exertion. BEGIN RECORDING
- Click on Record.
- Begin the test by opening either Stimulus 1 or Stimulus 2 on the NEURO10 computer.
On the NEURO10 computer, open the audio sample on the desktop “Stimulus1” or “Stimulus2” depending on the assignment of the subject in the pair. It should open in a program called CoolEdit and begin playing. If it does not begin playing there is a play button in the lower left corner of the window.
As soon as the sample opens, it will begin playing. You will see a moving cursor on the audio sample.
Insert a marker (F9) for each tone. IMPORTANT: There is a change in stimuli at the 5 minute mark. Insert a marker here at minute 5 for both Stimulus1 and Stimulus2.
- Click Suspend. After returning to baseline following the last tone, press suspend to pause the recording.
Make sure that your data is GOOD before quitting the
experiment.
- Click Done. A pop-up window with options will appear. Make your choice, and continue as directed. If choosing the “Record from another Subject” option: a) Attach the sensors per Set Up Steps 5, 6, and 7 and continue the entire lesson from Set Up Step 10. Each person will need to use a unique file name.
- Remove the sensors and clean-up.
END OF RECORDING
Remember to disconnect the GSR electrode and wash all of the gel out of the insets before replacing in the recording room
the I-Beam cursor, select an area from the start of the first inhale after the marker indicating the stimulus to the start of the next inhale (Fig. 9.14), and record the respiration rate (BPM) for stimulus 1a. Then, measure the distance between the start of the first inhale before the stimulus to the start of the previous inhale (i.e. a baseline measurement before the stimulus is delivered) and record the respiration rate (BPM) for stimulus 1a baseline.
Record these values on your
data sheet.
In the “change from baseline” cell, create a formula to create a percent change variable by dividing the stimulus by the baseline. For example, type in the cell “ = [click on the stimulus cell]/[click on the baseline cell] ”
as positive values, and chest deflation (exhalation) as negative values. Therefore, the start of inhalation is recorded as the beginning of the ascending positive waveform. Note : This measurement may be difficult to perform, depending on your data, because small dips in chest expansion can occur within the normal cycle. You must be able to distinguish the small dips from the big dips.
Fig 9.
ABOVE: Example of respiration response measurement (19.1) BELOW: Example of respiration baseline measurement (16.9)
- Also for the first stimulus, using the I- Bean cursor, select the data from the marker indicating stimulus 1 to the top of the GSR response to the stimulus. Record the mean Heart Rate and the p- p GSR values on your data sheet. NOTE THE DELTA T value. You must now select an equivalent length (same delta T) area of the baseline prior to the stimulus and record a baseline Heart Rate and GSR.
In the “change from baseline” cell, create a formula to create a percent change variable by dividing the stimulus by the baseline. For example, type in the cell “ = [click on the stimulus cell]/[click on the baseline cell] ”
- Repeat Steps 5 & 6 for each stimulus before the sensitization stimulus at minute 5, the sensitizations stimulus itself, and the stimuli following the sensitization stimulus.
ABOVE: Example of GSR (2.1) & Heart Rate (66.8) response measurements – note: same delta T (4.2 seconds). BELOW: Example of GSR (0.0) & Heart Rate (64.7) baseline measurements – note: same delta T (4.2 seconds).
DATA ANALYSIS COMPLETE – ENTER ONLY YOUR “Change from Baseline” DATA IN THE GROUP DATA SHEET ON THE DESKTOP OF THE NEURO4 COMPUTER IN THE NEUROSCIENCE LAB.
