System development for multichannel electrotactile stimulation on the lips

Multichannel pulsatile stimulation is essential for electrotactile presentation of spatiotemporal patterns in sensory substitution through the sense of touch. In this paper, a system for multichannel electrotactile stimulation is presented for studying electrotactile sensation on the lips, a site that has been shown to be highly sensitive but never been assessed for electrotactile applications. The system utilized a demultiplexing scheme to deliver voltage-clamped pulse waveforms to 32 channels corresponding to an array of 4x8 stimulators. Initial testing of electrotactile presentation on the lips was performed in human subject experiments on threshold measurement and two-line separation. For an array of hemispherical stimulators each 700 microm in diameter, the threshold values on the lower lip were averaged at only 8.2 V and intensities for well-perceived stimulation were averaged at around 14.2 V. The testing results suggested that lips were promising sites for electrotactile applications due to their high sensitivity to electrotactile stimulation at extremely low intensities.