Skin Conductance Response (SCR)

The Skin Conductance contains two components: the tonic, static „level“ and the phasic, fluctuating „reactions“, and these components are usually designated as Skin Conductance Responses (SCR).

While the “level” is represented well in the average of the measured values, the eSense Skin Response also measures the amount of Skin Conductance Response (SCR) per minute. In general, a higher number of SCR per minute is an indicator for higher stress. Value from experience which is in alignment with scientific literature[1] suggests that a “relaxed” frame is between 0 and 5 SCR per minute. From 6-9 SCR/min starts an animated state. From 10 or even from 16 SCR/min, a level of stress or even high stress can be assumed.

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[1] Boucsein, W. B. (2011). Electrodermal Activity (2. Aufl.). Berlin, Deutschland: Springer.

The SCR are great for comparing biofeedback-sessions to each other. If your goal for training is a reduction of stress, then the amount of SCR/min should decrease over several sessions. In the archive of the app, you can compare the different sessions to each other.

The average value in µS of a session is an indicator for the “level,” hence how high your basis level of tension or relaxion is. You should also try to lower this while you are doing stress reduction training. The average value also takes the SCR into consideration and is falsified with many SCR/min. You should, therefore, use as quiet a frame as possible without any SCR to determine your own “stress level” in µS.

We have colored the SCR/min in the eSense app. Low SCR are green or yellow and high SCR/min are orange or red. While making a measurement, the recognized SCR are colored within the curve. Two examples from our app:

In the right diagram, there is also the time in which the values rise, fall or have been steady. With rising stress, the curve rises more often and longer than it keeps steady or falls. This is also an ideal parameter to analyze and to compare biofeedback sessions.

The whole process of detecting and calculating the SCR is a cycle of four steps:

1. Listening state
2. Determining if the signal raise is really a SCR
3. Gathering and calculating SCR and listening asynchronously for SCR recovery phase
4. Initiate recovery phase and end of fluctuation

Listening state		Determining if the signal raise is really a SCR
Initiate recovery phase and end of fluctuation		Gathering and calculating SCR and listening asynchronously for SCR recovery phase

The 4 Steps in detail

1. Listening state

The cycle starts in the first step, the listening state. This is the standard default state.

2. Determining signal raise

There are two ways for detecting the start of an SCR start. The values could either raise slowly with a small step or very fast with a big amplitude. This creates the following to conditions:

1. The signal is constantly rising for 2 seconds 
2. The difference between the current signal and the pretended base value (the value that is considered to be the first value in the rising signal. But on this stage, it is not confirmed yet as a base value) is greater than 0.5 micro siemens.
   In simple words the app will react to a sudden signal raise and confirm it as the fluctuation start and will not wait for 2 seconds (as in the first condition above)

If the signal will fall just even 0.1 micro siemens during a raise, the app will drop out of this second step and return to the first step (the listening state) again. Otherwise it will continue with the next two steps 3 and 4.

3. Gathering and calculating SCR (fluctuation)

If one of the two conditions from the second step above are met, the app enters this third step, the fluctuation. The first signal of the fluctuation period is the base value of a fluctuation signal. During the whole fluctuation period, the app is detecting the amplitude which is constantly changing. Then the app starts to calculate the SCR events globally and within a one-minute time window. This results in the SCR/min value.

4. Initiate recovery phase

The fluctuation is considered to enter the recovery phase (the end of fluctuation) when the signal falls for more than 50% of the greatest amplitude of the fluctuation period. 

This is also the step where the color in the graph is changed (based on the quantity of SCR events that were occurring). The colors for the SCR background are also calculated (by dividing time intervals into equal segments and getting the sum of the SCR events from each segment).