With this electronic scheme can be tested a person whose status is modified in certain situations (as in the polygraph test) by "observing" biofeedback. Because a person's skin resistance depends on the state in which that person is, skin resistance increases with depth state of relaxation.
The electronic scheme presented, affects skin resistance frequency of oscillator built with transistor T2 . Both electrodes, with ring shape, are applied on two fingers of a hand. The more deep state of relaxation corresponds to a lower frequency sound that you will hear in your headset.