Spatial mapping of electrotactile sensation threshold and intensity range on the human tongue: Initial results

Abstract

We have developed a novel, tongue-based electrotactile brain-machine interface. Variability of the tactile sensation intensity across the stimulated area, however, limits the amount of reliable information transmission. We have conducted an experiment to characterize local sensitivity across the region stimulated by the array. From this data we have constructed an isointensity algorithm to compensate for the variability in electrotactile sensation levels across the stimulated area of the tongue.

Perceived Intensity and Discrimination Ability for Lingual Electrotactile Stimulation Depends on Location and Orientation of Electrodes

“…Consistent with findings from studies using a variable voltage stimulus (Tyler et al, 2009), our analysis revealed that Location and Subarray both affect perceived intensity ( P < 0.001) for a constant voltage stimulus across the tongue. On average, the perceived intensity of a constant voltage stimulus on a participant’s tongue was reported as highest in the anterior most medial region and was perceived as less intense in more posterior and lateral regions (Table 1, Figures 3–5).…”

“…Stimulation of the most anterior 2 cm of the tongue resulted in the highest perceived intensity and the best discrimination ability under the condition of constant voltage. Furthermore, electrotactile stimulation of medial tongue regions was perceived as more intense than stimulation of lateral regions consistent with previous studies (Maeyama and Plattig, 1989; Tyler et al, 2009; Wilson et al, 2012), Interestingly, it appeared that perception for electrotactile stimuli was best for regions just lateral to the midline rather than in the most medial region and the sensitivity and enhanced discrimination ability of this paramedial region extended beyond the most anterior tip of the tongue (Figures 3, 7). In future experiments, we would like to investigate this trend more closely by further subdividing the 1 cm 2 tongue regions analyzed in these studies.…”

“…Our current results add to work from other researchers who have labored to improve the perception of electrotactile stimuli on the tongue. In particular, this study compliments the work of Tyler et al (2009) who studied the sensitivity of the tongue to electrotactile stimulation and that of Chekhchoukh and Glade (2012) who demonstrated methods to improve sustained electrotactile perception. Our research indicates that changes in discrimination ability on the surface of the tongue should be considered when designing electrode arrays to be used to communicate information to a person.…”

“…The waveform used to stimulate the tongue in this study were based on results of previous studies indicating that multiple biphasic pulses grouped in short bursts result in comfortable, effective electrotactile stimulation (Kaczmarek and Tyler, 2000; Tyler et al, 2009; Kaczmarek, 2011). For our studies, we used a constant value of 5 volts for PA and an Outer Burst Period (OBP) of 36 ms, a PA of 5 volts, an Inner Burst Number (IBN) of 3, a Peak to Peak (PP) length of 10 μs, and an Inner Burst Period (IBP) of 150 μs.…”

“…Previous studies have been small (averaging eight participants each), and mostly centered on mapping the sensitivity of the tongue without analyzing electrotactile two-point discrimination ability (Lozano et al, 2009; Tyler et al, 2009; Wilson et al, 2012). These studies indicate that anterior-medial tongue regions have lower thresholds for electrotactile stimulation relative to posterior regions and sensitivity to electrotactile stimulation varies widely between individuals.…”