ABSTRACTThe present study demonstrates an impairment of habituation in schizophrenic patients on a measure of defensive responding to startling stimuli. The blink reflex component of human startle in response to 116dB(A) tones (40 msec, 1000 Hz) was monitored and distinguished from voluntary eyeblinks by a computer. With a background noise level of 70dB(A), 121 tones were given at varied intervals averaging 15 sec. All three groups tested, 25 presumed normals, 20 psychiatric patient controls and 22 schizophrenic patients, exhibited similar responses to the first several stimuli. However, while normals and patient controls exhibited roughly 70% decrements in response amplitudes across trials, schizophrenic patients habituated by less than 50%. An unexpected finding was that the latency‐to‐peak values for normals and controls were non‐monotonically related to both trial number and response amplitudes. That is, latencies first increased and then decreased as the same stimulus was repeated. As with amplitude habituation, this phenomenon was also delayed in the schizophrenic patients. The results indicate that schizophrenic patients have abnormal habituation of defensive responses to exteroceptive stimuli. Possible links between abnormal habituation and symptom formation in schizophrenia are disc