Enhancement of Subjective Mechanical Tactile Intensity via Electrical Stimulation

Naturalistic tactile sensations can be elicited by mechanical stimuli because mechanical stimulation reproduces a natural physical phenomenon. However, a mechanical stimulation that is too strong may cause injury. Although electrical stimulation can elicit strong tactile sensations without damaging the skin, electrical stimulation is inferior in terms of naturalness. Here, we propose and validate a haptic method for presenting naturalistic and intense sensations by combining electrical and mechanical stimulation. Prior to the main experiment, we measured the appropriate temporal gap between the two stimuli such that they are perceived as simultaneous, since nerve activity directly elicited by electrical stimulation is generally considered to be perceived faster than mechanical stimulation. We confirmed that enhancement of subjective strength took place when two stimuli were given simultaneously. The main experiment with simultaneous electrical and mechanical stimulation confirmed that addition of electrical stimulation enhances the sensation of mechanical stimulation, and participants' comments implied that electrical stimulation was interpreted as part of the mechanical stimulation.