Abstract
The electrical response of the human brain to auditory stimulation was studied by means of Dawson's method of superimposition. The stimulus applied was a continuous tone of 1000 c. p. s. of short duration or a click of high intensity. Though the sound stimulus had on- as well as off-effect, the present experiment was concerned mainly with the on-effects.
1. The evoked response was triphasic activity beginning with the electronegativity of the pick-up electrode against the indifferent lead on the earlobe. At the highest intensity applied of the stimulus the first negative deflection was started at about 90 msec. after the onset of the stimulus and the peak of the second positive deflection was reached at about 150 msec. These values were not greatly reduced by increasing the intensity of stimulus.
2. The amplitude increased almost linearly with the stimulus intensity in db units.
3. The evoked potential was found widely distributed over the scalp, the amplitude being maximal at the vertex. The unresponsiveness of the forehead region was inferred from the finding that the response from that region was reverse in phase to those from the remaining regions.
4. The refractoriness of the brain following the sound stimulus was measured by applying two clicks of equal intensity as a conditioning and testing stimulus respectively. It was found that the absolutely refractory period was about 0.5 seconds.
5. When a subject was anesthetized with a barbiturate, the evoked potential increased in size until the stage of 14-per-sec. activity was reached. At the stage of slow waves the evoked potential was lost sight of.
6. An experiment of electroencephalographic conditioning was made on a subject who responded to the sound stimulus with an evoked on-response followed by a short train of β-waves. A photic stimulus of low intensity and a strong sound of short duration were used as conditioned and unconditioned stimulus respectively. The time interval between two stimuli was about 5 seconds. After a number of application of the combined stimulus it was found that only β-activity appeared as a conditioned excitation of the brain, but that no potential change in form of the so-called evoked response appeared upon conditioned stimulation.
My hearty thanks are due to Prof. K. Motokawa who furnished me with guidance and criticism in regard to this work.
