This simple circuit makes it possible for a particular type of biofeedback.
The principle underlying the observation that a person’s skin resistance depends on the extent to which the person is relaxed; skin resistance increases with the depth of relaxation state.
The skin resistance influence the oscillator frequency that is built with unijonction transistor T2. Both electrodes, which form a ring, are applied to two fingers of a hand. A speaker is used for hearing the sound whose height is a measure of the state of relaxation. The more profound state of relaxation is, the sound frequency is lower.
The second oscillator, built with transistor T1, also produce a sound. In this case you can adjust the height of sound with potentiometer P1, at the frequency of the other oscillator, corresponding to the deepest state of relaxation. If the signals of the two systems are run separately in a stereo headset, the maximum relaxation is achieved when the right tone sounds at the same height at the left.