Before starting an Electrodermal Ectivity (EDA) measurement with the BITalino sensor we recommend you to check if you are following all our recommendations (below).
There is normally no need for pretreatment of the skin where active recording will take place, unless the skin is dirty. If that’s the case you can clean it lukewarm water prior to the electrode attachment.
Washing with soap is not recommended because it may cause swelling of the epidermis, impacting this way the results. We also recommend some precaution in using alcohol-based solutions to clean the skin once the skin salt concentration may change. Use it only in case of the skin contain excessive oil (Source: Society for Psychophysiological Research Ad Hoc Committee on Electrodermal Measures, et al. “Publication recommendations for electrodermal measurements.” Psychophysiology 49.8 (2012): 1017-1034)
EDA measurements are very sensitive to changes in electrode-to-skin conductivity. So never re-use electrodes.
Try to be consistent in using electrodes, i.e., if you start an experiment with pre-gelled and dischargeable electrodes, keep the same as reusable ones during your set of experiments (unless the goal is to compare the electrodes’ performance). You might notice differences in the values depending on the type of electrodes you’re using.
The BITalino EDA sensor is designed to acquire the change of skin activity such as sweat with two measuring electrodes. One example is the placement of the electrodes on the anterior side of the hand on two adjacent fingers of interest (see Fig. 1). The electrodes are then connected to the sensor cable of the EDA sensor.
Figure 1: Example electrode placement of the assembled version on the anterior side of the hand on the index and middle finger (left) and below the thumb (right).
Sensors set-up in BITalino
When using BITalino we do not recommend the use of more than one EDA sensor at the same time.
Due to the technical design of the EDA sensor of the BITalino, you may notice some irregularities in this signal when working with it together with other ExG sensors (e.g., electrocardiography (ECG), electromyography (EMG), electroencephalography (EEG), etc.) that require the use of a reference cable (Vref).
When you attach the Vref of the ExG sensor, you will have a reference at two different points on the body, once the EDA sensor has its own intrinsic reference as well. These two reference points might interfere in the EDA resistance measurements, which will drop significantly, while acquiring the signals at the same time.
To overcome this issue, we recommend using ExG sensors also with 2-lead electrode cables. You can also use with 3-lead electrode, then you must disconnect the midpoint of the ExG sensor (i.e. the Vref, usually labeled with white sleave) from the body and leaving the electrode in the air. This procedure has no effect on the ExG signals measurement.