 The cause is thought to be thermoelastic expansion of portions of auditory apparatus, and the generally accepted mechanism is rapid (but minuscule, in the range of 10−5 °C) heating of brain by each pulse, and the resulting pressure wave traveling through the skull to the cochlea.In 1975, an article by neuropsychologist Don Justesen discussing radiation effects on human perceptions referred to an experiment by Joseph C. Sharp and Mark Grove at the Walter Reed Army Institute of Research during which Sharp and Grove reportedly were able to recognize nine out of ten words transmitted by "voice modulated microwaves".Since the radiation levels approached the (then current) 10 mW/cm² limit of safe exposure, critics have observed that under such conditions brain damage from thermal effects of high power microwave radiation would occur, and there was "no conclusive evidence for MAE at lower energy densities".