An initial study on lip perception of electrotactile array stimulation.

We conducted an initial study on tactile sensory characteristics of the lips by applying electrotactile array stimulation on the center surfaces of the upper and lower lips. We performed experiments of threshold measurement and rating of two-line separation to evaluate the tactile sensitivity and spatial discriminating ability of the lips, respectively. Three stimulator arrays of different sizes presented electrotactile patterns on the lips of eight subjects (six male, two female) to measure the electrotactile performance in relation to stimulator size and spacing. Experimental results showed that the lips required very low intensities for effective electrotactile stimulation. As the stimulator diameter increased from 75 micrometers to 1.55 millimeters, the average stimulation intensity at the threshold level decreased from 12.5 to 6.3 V for the lower lip and from 13.3 to 7.1 V for the upper lip. Meanwhile, the two-line separation rating experiment showed that both upper and lower lips possessed high spatial discriminating ability. The average percentages of correct rating of two adjacent lines ranged from 80.5% to 88.2% on the two stimulator arrays with center-to-center spacing of at least 2.40 mm. In addition, sensitivity analysis indicated that the upper lip slightly outperformed the lower lip in spatial discrimination.