POLYGRAPH
BIOFEEDBACK
GALVANIC SKIN RESPONSE (GSR)
THE POLYGRAPH
Polygraph – many measures (many – poly, graphein – to write)
- recording at the same time the changes of several biological
parameters (usually GSR, blood pressure, heart rate, respiratory frequency)
in order to find abnormal changes during different situations (ex. emotional
state of the person)
GSR - the variation of the electrical resistance of the skin due to the degree of
activation of the autonomic nervous system (ANS stimulation increases the
secretion of sweat, rich in ions). It represents one of the electrodermal
answers – EDA.
Polygraph – lie detector – can interpret how people respond (physiologically)
to certain questions. It is based on the assumption that telling a lie is an
emotional stress.
GALVANIC SKIN RESPONSE
( GSR)
When measuring skin conductance, there is the skin conductance level
(SCL) and skin conductance response (SCR). SCL is the slow varying
skin conductance value, changing over the course of minutes. SCR is the
fast varying skin conductance value, changing over the course of
seconds. The SCR that rides on top of the SCL reflects a person's mental
response to various stimuli.
Normal value:
Latency <3 sec
Amplitude: μS
Rise time : 1-3 sec
Half recovery time: 2-10 sec
THE POLYGRAPH IN BIOPAC SYSTEM
1.Objectives: evaluation of the changes in ANS activation during different emotional
states.
2. Materials:
- BIOPAC cables : SS5LA , SS4L, SS3L ( GSR transducer, respiration
transducer, pulse transducer)
- electrode gel
- BIOPAC acquisition unit
3. Preparation for recording:
- attach the respiratory transducer around the chest
- attach the GSR transducer and pulse transducer to the fingertips.
- the subject should breath slowly, be relaxed and should not look at the screen.
The questions should be answered with minimal movements (every external
stimulus can change the emotional state of the subject so unnecessary noises and
movements through the room should be avoided). The answer will be YES/NO.
- perform the calibration for the recording.
THE POLYGRAPH
Recording: three different situations
1. SCL , habituation - we will record traces without questions then we will
record habituation to the same repetitive question (Your name is XY?)
2. Neutral questions – we will measure SCL and SCR during neutral questions
3. Mixed questions – we will measure SCL and SCR during ten neutral and
emotional questions (first should be neutral but the next questions may be
neutral or with emotional content – in this situation the amplitude will
increase and the rise time will decrease)
Biofeedback

Biofeedback – the process of relaying physiological information (usually
in a graphical or audible format) back to people as they perform various
behaviors. It developed as a training method for the control of the body
functions. The devices used constantly monitor the function of the body
(blood pressure, heart rate, activation of ANS- GSR) and provide real-time
information about their changes.
- 2 types – physiological biofeedback
- psychological biofeedback
(physiological biofeedback relies on physical changes such as posture
shifts and closing eyes to induce relaxation; psychological biofeedback
depends on cognitive tasks to alter one’s physiological state)
Biofeedback
Biofeedback
1.Objectives: to asses the capacity of the voluntary control over the sympathetic
activation
2. Materials:
- BIOPAC cables : SS2L , SS3L ( ECG cables : white, black, red; GSR
transducer )
- electrode gel
- BIOPAC acquisition unit
3. Preparation for recording:
- place the ECG cables on right foot-black, left foot-red and right forearm -white
(we use ECG electrodes to calculate the heart rate).
- attach the GSR transducer to the fingertips.
- perform the calibration for the recording (during the setup breath normally until
you hear a “beep” and take four deep, rapid breaths; after that relax and breath
normally for the remainder of the 30 seconds).
Biofeedback
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During the recording, the GSR and heart rate will be plotted in X-Y mode
(one signal is plotted on the horizontal axis – GSR; the other signal is
plotted in vertical axis - HR).
The combination between HR and GSR will be presented on the screen as
a dot (the position of the dot will reflect the level of arousal and the level of
HR). As the heart rate will increase the dot will move closer to the top of
the screen. If the GSR will increase the dot will move towards the right
edge of the screen.
We will use specific tasks to modify the position of the dot
- Relax your posture !
- Clench your fists !
- Breath in and out very slowly !
- Imagine yourself relaxing seaside, feel the warmth of the sun!
- Think about someone you dislike !