Thank you for sharing Susan Shore's answer. It helped me to understand things better.
There are nice cheap gel pads to be used as electrodes available. People in Susan Shore's team decided to tape the wire to the skin. This then has a huge impact on the study participants as the tape helps habituate to the electric pulses which don't need to be felt at all for the device to work. After all, they feel the tape so how could they feel electric pulses... you cannot make this shit up.
You can get yourself a cheap EMS device and check if it is possible for you to habituate to your threshold signal level. I can tell you cannot. But prove me wrong.
A couple of pages back somebody shared a link to GitHub for the source of TinnTester (or whatever it is called). He said that the project was bit of a mess. I downloaded the project and after spending some time trying to figure out what it was actually doing, I came to conclusion that the "bit of a mess" is a huge understatement. I've been coding in IT for over 20 years and have never seen anything like that. The zipped up project package was 1 GB. If I figured correctly, the software is a questionnaire playing sounds. A couple of screens with buttons and radio boxes. 1 GB of compressed data for that! The code by itself was written by somebody one step above Hello World skill proudly presenting himself as PhD. Although this software has probably nothing to do with Susan Shore's team, it shows how ineffective and incompetent a part of the academia is.