1. A device for analyzing the EEG signal of a subject in response to periodic stimuli; the improved means for analyzing the EEG signal comprising: (A) a timer and switch means for passing the EEG signal only during at least one time interval of preset duration beginning a predetermined time after each of a plurality of periodic stimuli, thereby obtaining a gated EEG signal, (B) rectifier means for dividing the gated EEG signal into positive-going signals and negative-going signals, (C) first integrator means for integrating the positive-going signals, (D) second integrator means for integrating the negative-going signals, and (E) means for algebraically combining output signals from the first and second integrator means for measuring the degree of response of the subject to the periodic stimuli.