Effect of Frequency on Perception Currents

The predominating sensation produced by gradually increasing direct current is warmth in the palm of the hand or wrist. Sensations caused by alternating currents below 10,000 cycles are characterized by a tingling or pricking sensation which is localized in the area adjacent to the point of contact, and at very low frequencies the muscles tend to follow the alternations of the current waveform. For frequencies between 10,000 and 100,000 cycles, the sensations are similar to those at the power frequencies, but they are less intense, and perception occurs over larger areas around the point of contact. An abrupt change in the response occurs between 100,000 and 200,000 cycles when the sensation becomes one of internal heating, and heating is believed to be the only sensation produced by currents in excess of 200,000 cycles. The current required for perception increases with increasing frequency, and between about 1,000 and 100,000 cycles the current is nearly proportional to frequency. Approximately 150 men were used in these investigations and it is believed that a sufficent number were used to permit valid statistical predictions to be made, not only for the particular group tested, but also for a normal cross section of the adult male population of the country.