Electrocutaneous code pairs for artificial sensory communication systems

Pairs of electrocutaneous codes suitable for dual-channel sensory communication systems were compared using a dual-channel electrocutaneous tracking task. The tracking task required the test subject to dynamically respond to changes in the tactile sensation being modulated by two independent pseudorandom signals, one for each channel. The rule (or method) by which the signals changed the tactile sensations was called an electrocutaneous code. Four frequency variation codes and two intensity variation codes were paired in different combinations and then checked as to their effectiveness for sensory communications. The experimental protocol used a balanced incomplete block design which involved 24 subjects testing 3 of 8 code pairs each. Although the variance in the tracking performances between subjects was larger than the differences between the code pairs, learning rates for the various pairs were significantly different. The easiest one to learn was the Low Pulse Rate Modulation Code paired with itself. Other findings included the general superiority of monophasic stimulation code pairs over biphasic stimulation code pairs, the need for placement of the two electrodes on different dermatomes in order to achieve satisfactory dual-channel communications, and the greater sensitivity to electrocutaneous stimulation of the ventral side of the forearm versus its dorsal side.