There are several aspects of the EDA that one can measure:

• SC = Skin conductance. Measured in microsiemens or micromhos (the reciprocal of resistance, ohm)
• SCL = tonic changes in SC
  • note: we will generally not focus on SCL for a number of reasons. These include the fact that SCL will drift over time due to both physiological (SCRs can raise SCL) and non-physiological (polarization of electrodes in DC recording) factors.
• SCR = phasic changes in SC
• NS-SCR = SCRs that occur without any identifiable eliciting stimulus
• ER-SCR = SCR that is evoked by a specific eliciting stimulus

The onset of an ER-SCR will occur 1 to 3 seconds after the event and will have a rise-time (i.e. from initial deflection to peak amplitude) of 0.5 to 5 seconds.

10% of participants will be non-responders. That is, these individuals will not show an appreciable SCR.

Moreover, there are several ways to evaluate these responses. With regard to SCRs, one can

• evaluate the peak amplitude of the SCR
• evaluate the rise-time of the SCR
• evaluate the recovery time of the SCR
  • note: generally this is measured to 67% or 50% recovery because after an SCR there will likely be an increase in SCL. That is, the response will not completely recover to pre-SCR baseline.
• evaluate the frequency of NS-SCRs within a given epoch
• evaluate the rate of SCR habituation

• Introduction to electrodermal activity
• A Guide for Analysing Electrodermal Activity (EDA) & Skin Conductance Responses (SCRs) for Psychological Experiments
  
• Electrodermal activity measurements
  
• Biopac Electrodermal Response Basics
  
• EDA (GSR) subject preparation
  
• Guidelines for GSR, EDA, EDR, SCL, and SCR

• Power on the MP150
• Ensure that the EDA100C (Electrodermal Activity) amplifier is attached and set to channel #3

1. Connect two LEAD110A leads into the EDA100C
   1. Plug one lead into the Vin+ port and the other into the Vin- port

1. Use electrode prep swab to clean the index and middle fingers of the participant's non-dominant hand
2. Remove two EL507 electrodes.
   1. Put extra GEL101 on them
   2. You must use the specific SCR GEL101. Other conductive gels (e.g. the EEG gel) are not appropriate.
3. Place them on the middle phalanx of the participant's index and middle fingers. Refer to the image below
4. Attach the pinch connector of one LEAD110A to the EL507 electrode on the middle finger, and the other to the EL507 electrode on the pointer finger.
5. Wait at least five minutes before recording. The electrolyte gel will continue to penetrate into the stratum corneum, which will cause a drift in the ECL (specifically, increased conductivity).