An evoked response audiometer method and apparatus in which a patient receives an auditory stimulus signal comprising a carrier frequency which is periodically amplitude modulated and frequency modulated whereby the stimulus is at least substantially frequency specific, the brain potential signals of the patient evoked by the auditory signal being sampled to determine whether phase locking to the modulated auditory signal has occurred, the auditory signal being selectively controlled to advance or delay one modulation with respect to the other modulation to cause enhancement of the evoked response to the auditory stimulus (Figs. 12 to 15).
PHASE LOCK EVOKED RESPONSE AUDIOMETER