Muscular action potentials in both forearms were measured while Ss, instructed not to respond, were exposed to loud sounds. 1. Such stimuli "may be said to produce two responses, called a and b . . … 2. The a-response has a latency of about 0.1 sec., reaches its peak during the next 0.1 sec. after the stimulus onset, and in large part disappears during the next 0.5 sec. 3. The a-response shows marked and rapid adaptation, practically disappearing with a half dozen stimulations two min. apart. 4. The a-response varies with stimulus intensity, and probably would not appear with a stimulus of much less than the 90-100 db. at 500 cycles here used. 5. The b-response, the latency of which cannot be determined exactly from these data, reaches its maximum generally about one sec. after the onset of the stimulus, and on the average stays at that level for about another sec., thereupon declining. 6. The b-response is not affected by stimulus intensity or repetition within the limits of the experiment. 7. Both a- and b-responses are closely related to the state of tension existing just before the delivery of the stimulus . . …" (PsycINFO Database Record (c) 2006 APA, all rights reserved)