A novel pneumatic skin sensory stimulator and its application to a two-point discrimination test

We have developed a tactile stimulation system that can apply air puffs locally to any two points on a skin's surface. This system consists of an air output device and a reaction recording device, both controlled by dedicated software. The air output device is equipped with a microcontroller ESP32, which can produce an airflow from two ports by controlling the intensity of the compressed air, the duration of its output, and the inter-trial time interval between applications. The reaction recording device is equipped with a push-button to record the subject's response when the air is applied to the skin. We verified the applicability of this system by a two-point discrimination test. In 14 healthy human subjects, the shortest distance at which they correctly answered that the given air was at two points was 35 mm. When we applied the air at 30 mm, the majority of the human subjects answered incorrectly that the air was only at one point when in fact it was at two points. This result was in close agreement with previously reported results obtained by direct skin stimulation methods.