Abstract: Biofeedback training of a subject may be achieved by monitoring the skin potential response of the subject and by shaping the monitored response so that a feedback signal is generated only if the response exceeds pre-established upper and lower limits which may be selectively increased or decreased. Biofeedback apparatus for implementing this technique includes electrodes for sensing the skin potential, an amplifier for amplifying the signal and feeding the signal into a pair of variable comparators which provide output when the response exceeds preset upper and lower limits. The outputs, in turn, provide a feedback signal either audio or visual, or to serve as inputs to auxiliary instrumentation. No feedback signal is produced as long as the monitored signal is within the selected limits. The magnitude of the responses may be quantified to the extent that they exceed the preset levels. The audio feedback signals may be recorded on a common audio cassette recorder.