Tapping and Rubbing: Exploring New Dimensions of Tactile Feedback with Voice Coil Motors Kevin A. Li 1 , Patrick Baudisch 3 , William G. Griswold 1 , James D. Hollan 2 1 Computer Science & Engineering University of California, San Diego {k2li, wgg}@cs.ucsd.edu 2 Cognitive Science University of California, San Diego hollan@cogsci.ucsd.edu 3 Microsoft Research Redmond, WA baudisch@microsoft.com ABSTRACT Tactile feedback allows devices to communicate with users when visual and auditory feedback are inappropriate. Un- fortunately, current vibrotactile feedback is abstract and not related to the content of the message. This often clashes with the nature of the message, for example, when sending a comforting message. We propose addressing this by extending the repertoire of haptic notifications. By moving an actuator perpendicular to the user’s skin, our prototype device can tap the user. Moving the actuator parallel to the user’s skin induces rub- bing. Unlike traditional vibrotactile feedback, tapping and rubbing convey a distinct emotional message, similar to those induced by human-human touch. To enable these techniques we built a device we call soundTouch. It translates audio wave files into lateral mo- tion using a voice coil motor found in computer hard drives. SoundTouch can produce motion from below 1Hz to above 10kHz with high precision and fidelity. We present the results of two exploratory studies. We found that participants were able to distinguish a range of taps and rubs. Our findings also indicate that tapping and rubbing are perceived as being similar to touch interactions ex- changed by humans. ACM Classification: H5.2 [Information interfaces and presentation]: User Interfaces, Haptic I/O; B 4.2 Input Out- put devices. General Terms: Design, Human Factors Keywords: force feedback, haptics, vibrotactile, user inter- faces, voice coil motor. INTRODUCTION AND MOTIVATION Vibrotactile feedback has been widely employed for eyes- free communication, which is particularly valuable in mo- bile scenarios. When auditory feedback is socially inappro- priate [12] or used for other cues, vibrotactile feedback can be the best or even the only channel that allows a device to communicate with the user [14]. However, current implementations of vibrotactile feedback are limited. Vibrotactile feedback can convey a variety of signals, but these are generally perceived as conveying ur- gency. While this is appropriate for alerting users, it might be less appropriate for notifying users about a non-urgent, enjoyable event, such as the receipt of a text message from a close friend. It seems particularly inappropriate if the tac- tile ring is the message, such as when trying to communi- cate “I am thinking of you” over a messaging system. rubbing head (under user’s hand) soundTouch Figure 1. Rubbing interaction implemented using our sound- Touch prototype. We propose extending the haptic vocabulary of notification and messaging devices with tactile messages inspired by human-human communication. We make two contributions: 1. We introduce two new types of haptic feedback, tap- ping and rubbing. These are modeled after their hu- man-human counterparts and designed to convey atten- tion and comfort, rather than urgency. 2. We report the results of a user study demonstrating (a) that users indeed perceive the above modalities as tapping and rubbing as experienced in human interac- tion and (b) that users can distinguish a wide range of tapping and rubbing frequencies and amplitudes. The proposed techniques cannot be implemented with tradi- tional vibrotactile method, because these methods cannot produce sufficiently low frequencies. Below 20Hz, the off- set (eccentric) DC motors used in these devices can no longer produce noticeable displacements. To implement rubbing and tapping we therefore developed a haptic device Permission to make digital or hard copies of all or part of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation on the first page. To copy otherwise, or republish, to post on servers or to redistribute to lists, requires prior specific permission and/or a fee. UIST’08, October 19–22, 2008, Monterey, California, USA. Copyright 2008 ACM 978-1-59593-975-3/08/10...$5.00.