The differential EMG amplifiers permit low interference recording from electrodes without shielding. For electrical stimulation, amplifiers are modified so the electrical stimulus died out within 8 ms so it did not interfere with the EMG signal. After preliminary testing showed that the order of electrical or mechanical stimulation did not bias outcome, mechanical stimulation which caused less pain and habituation preceded electrical testing in the 19 comparisons. Blink reflexes elicited by mechanical stimulation caused minimal discomfort to the subjects. A measurement series consists of 10 taps to the supraorbital notch on each side to elicit BRL R-1 right and left.
Grip strength is measured for both hands using a dynamometer calibrated in kilograms.
Vibration sense of the outstretched index finger and great toe was measured to extinction against the author's right index finger and thumb with a 128 Hertz tuning fork. The threshold test is used with 80 light points tested per eye which takes 20 to 30 minutes for both eyes. Top Hearing is measured at frequencies from 500 to 8,000 Hz using a standard manual audiometer by a skilled technician. Thresholds at each frequency are established using a bracketing steps approximation algorithm. Results are expressed as the sum of hearing loss at each frequency for each ear.