Surfpad: Riding Towards Targets on a Squeeze Film Effect Géry Casiez 1,3,4 , Nicolas Roussel 3 , Romuald Vanbelleghem 3 & Frédéric Giraud 2,3,4 1 LIFL, 2 L2EP, 3 INRIA Lille & 4 University of Lille, France gery.casiez@lifl.fr, nicolas.roussel@inria.fr, frederic.giraud@polytech-lille.fr ABSTRACT We present Surfpad, a pointing facilitation technique that does not decrease target distance or increase target width in either control or display space. This new technique oper- ates instead in the tactile domain by taking advantage of the ability to alter a touchpad’s coefficient of friction by means of a squeeze film effect. We report on three experiments comparing Surfpad to the Semantic Pointing technique and constant control-display gain with and without distractor tar- gets. Our results clearly show the limits of traditional target- aware control-display gain adaptation in the latter case, and the benefits of our tactile approach in both cases. Surfpad leads to a performance improvement close to 9% compared to unassisted pointing at small targets with no distractor. It is also robust to high distractor densities, keeping an aver- age performance improvement of nearly 10% while Seman- tic Pointing can degrade up to 100%. Our results also sug- gest the performance improvement is caused by tactile in- formation feedback rather than mechanical causes, and that the feedback is more effective when friction is increased on targets using a simple step function. ACM Classification Keywords H.5.2 [Information interfaces and presentation]: User inter- faces - Graphical user interfaces. General Terms Design, Performance, Experimentation, Human Factors Author Keywords Pointing facilitation, target-aware, control-display gain adaptation, squeeze film effect INTRODUCTION Pointing is a fundamental task of modern human computer interfaces and has been extensively studied by the HCI re- search community. Fitts’ law has proven to be one of the most robust and widely adopted models in this area [29]. It expresses the movement time to acquire a target of width W at a distance D as a linear function of the index of difficulty ID = log 2 ( D W + 1). Numerous techniques have been proposed that attempt to beat Fitts’ law, i.e. to make virtual pointing easier than it is in the physical world [5]. Most of these techniques at- tempt to decrease D, to increase W , or both. Most of them are also inherently target-aware [34]: they take advantage of some knowledge about the size and position of the tar- gets and sometimes modify them. In cases where pointing involves the indirect control of a visual cursor, some tech- niques operate by dynamically adapting the control-display gain CDgain = V cursor /V device [12]. Other techniques sup- plement the visual display with auditory or haptic feedback. Yet despite their demonstrated efficiency in simple config- urations, most target-aware pointing techniques are difficult to use in practice. One of the key problems that affects them in real-life situations is the potential interferences caused by intervening targets on the way to the primary one (distrac- tors), a problem that is still largely understudied. In this paper, we present Surfpad, a pointing facilitation technique that does not decrease D or increase W in either control or display space. This new technique operates in- stead in the tactile domain by taking advantage of the ability to alter the coefficient of friction of a particular touchpad, the STIMTAC [9], by means of a squeeze film effect (Figure 1). We report on three experiments comparing Surfpad to the Se- mantic Pointing technique [10] and constant control-display gain with and without distractor targets. Our results clearly show the limits of traditional target-aware CD gain adapta- tion in the latter case, and the benefits of our tactile approach in both cases. Our results also suggest the performance im- provement is caused by tactile information feedback rather than mechanical causes, and that the feedback is more effec- tive when friction is increased on targets using a simple step function. smooth smoother Figure 1. The squeeze film effect: controlled vibration of a surface creates an air film which reduces its coefficient of friction. CHI 2011 • Session: Touch 2: Tactile & Targets May 7–12, 2011 • Vancouver, BC, Canada 2491 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. CHI 2011, May 7–12, 2011, Vancouver, BC, Canada. Copyright 2011 ACM 978-1-4503-0267-8/11/05....$10.00.