24 Ss lay quietly on cots and listened to 12 tones given at about 2-min. intervals, and of 70, 90, or 100 db intensity. S was instructed to respond at the end of each of 6 tones by pressing a button under his right forefinger, and not to respond at all to the other 6 tones. Electrodes were placed over the extensor muscles in the forearm and on the upper arms, and integrated action potentials were recorded. "Telling the Ss to respond heightened the pre-stimulus tension in the arm to be used. Two stimulus effects, called the a- and b-responses, in the first and later parts of the two-second period were analyzed. The first of these is part of the 'startle pattern,' the second is evidently the 'set' reaction . . … Both show a slight adaptation. Both vary with stimulus intensity whether the S is going to make a finger movement or not. When the S is going to execute that movement, these fore-period reactions are very much larger in the arm that is to respond, showing that instructions do modify the antecedent effects. Much, if not all, of this increase seems to take place because the preliminary tension level is higher." (PsycINFO Database Record (c) 2006 APA, all rights reserved)