How can I calculate skin conductance from voltage readings in my research study?

[tentativetitle]

I am collecting skin conductance data for a research study. For this, we apply a constant voltage (5v) to a participants finger and then measure the voltage at another finger (or I think this is what is happening, there is also something about a resistor in there [see attached schematic]).

The software I am using is giving me readings of the voltage being measured on the second electrode, but I need to convert this to conductance. The attached schematic has a formula for doing this - R = [(+sig) / 5 - (+sig)]6M6 - but I don't understand it. I believe that the +sig is the output that I am getting in the software, which would just leave the 6M6 as the term that I don't know. Can anyone shed light on this for me?

Thanks!

 

[berkeman]

I am collecting skin conductance data for a research study. For this, we apply a constant voltage (5v) to a participants finger and then measure the voltage at another finger (or I think this is what is happening, there is also something about a resistor in there [see attached schematic]).

The software I am using is giving me readings of the voltage being measured on the second electrode, but I need to convert this to conductance. The attached schematic has a formula for doing this - R = [(+sig) / 5 - (+sig)]6M6 - but I don't understand it. I believe that the +sig is the output that I am getting in the software, which would just leave the 6M6 as the term that I don't know. Can anyone shed light on this for me?

Thanks!

Welcome to the PF.

I'm glad to see that you are incorporating the 10uA max safety feature into your GSR project!

But, shouldn't you be making an AC measurement? DC measurements have issues with polarization altering the measurements...

 

[tentativetitle]

That is a good point. According to this publication: "Publication recommendations for electrodermal measurements", it is pretty common to use DC for gsr, but that AC may be preferable, because the polarization issue with the DC can cause drift in the signal.

I will be using measurements of about 4 seconds each in analysis (the four seconds after a given image is shown to the participant) and each of these 4 second chunks will be baseline corrected, using the average activity 1 second before the picture as the baseline. Hopefully this will minimize the measurement drift due to DC, but it sounds like AC would be preferable - something to consider when I get my own lab and purchase equipment.