LipNotif: Use of Lips as a Non-Contact Tactile Notification Interface Based on Ultrasonic Tactile Presentation

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We propose LipNotif, a non-contact tactile notification system that uses airborne ultrasound tactile presentation to lips. Lips are suitable for non-contact tactile notifications because they have high tactile sensitivity comparable to the palms, are less occupied in daily life, and are constantly exposed outward. LipNotif uses tactile patterns to intuitively convey information to users, allowing them to receive notifications using only their lips, without sight, hearing, or hands. We developed a prototype system that automatically recognizes the position of the lips and presents non-contact tactile sensations. Two experiments were conducted to evaluate the feasibility of LipNotif. In the first experiment, we found that directional information can be notified to the lips with an average accuracy of ± 11.1° in the 120° horizontal range. In the second experiment, we could elicit significantly different affective responses by changing the stimulus intensity. The　experimental results indicated that LipNotif is practical for conveying directions, emotions, and combinations of them. LipNotif can be applied for various purposes, such as notifications during work, calling in the waiting room, and tactile feedback in automotive user interfaces.