Using modified pore electrodes and an amplifier and recording system the sensitivity of which is as high as can be obtained at present with electron tube amplification where the base line is to remain steady, the author was unable to obtain any evidence for the appearance of increased muscular tension in either the muscle which is being used for the response or in its antagonist during the warning period preceding a simple or choice reaction. The actual response is characterized by the nearly simultaneous appearance of action potentials in the responding muscle and in its antagonist. These potentials first make their appearance at a minimum of about 60 ς before the appearance of actual movement in the arm. The two or three preliminary small discharges are quickly followed by larger ones which may be predominantly large in the muscle effecting the response. (PsycINFO Database Record (c) 2006 APA, all rights reserved)