Surface Haptics

Electrovibration, a technology capable of inducing programmable haptic sensations on physical surfaces like touchscreens, has yet to fulfill its potential due to limitations in our scientific understanding. We focus on developing methods to achieve consistent, controllable, and perceivable interactions using this technology. 

Ongoing projects: 

Related Publications

Finger Motion and Contact by a Second Finger Influence the Tactile Perception of Electrovibration

Electrovibration holds great potential for creating vivid and realistic haptic sensations on touchscreens. Ideally, a designer should be able to control what users feel independent of the number of fingers they use, the movements they make, and how hard they press. We proved for the first time that both the number of contacting fingers and whether each finger moves significantly affect what the user feels. Part of this change comes from the fact that relative motion greatly increases the electrical impedance between a finger and the screen. These findings help lay the groundwork for delivering consistent haptic feedback via electrovibration.

Effective utilization of electrovibration can only be accomplished by simultaneously investigating both the physical and perceptual aspects of the finger-touchscreen interaction. Towards this goal, present work blends the available knowledge on electromechanical properties of the human finger and human tactile perception with the results of new psychophysical experiments and physical measurements. By following such an approach that combines both theoretical and experimental information, the study proposes new methods and insights on generating realistic haptic effects, such as textures and edges on these displays. 

A Novel Texture Rendering Approach for Electrostatic Displays

Generating realistic texture feelings on tactile displays using data-driven methods has attracted a lot of interest in the last decade. However, the need for large data storage and transmission rates complicates the use of these methods for future commercial displays. Here, we propose a new texture rendering approach that can compress the texture data significantly for electrostatic displays. Using three sample surfaces, we first explain how to record, analyze and compress the texture data, and render them on a touchscreen. Then, through psychophysical experiments conducted with nineteen participants, we show that the textures can be reproduced by a significantly fewer number of frequency components than the ones in the original signal without inducing perceptual degradation. 

Effect of Remote Masking on Detection of Electrovibration

Here, we investigated whether it is possible to change detection threshold of electrovibration at fingertip of index finger via remote masking, i.e. by applying a (mechanical) vibrotactile stimulus on the proximal phalanx of the same finger. We found that vibrotactile masking stimuli generated sub-threshold vibrations around fingertip, and hence did not mechanically interfere with the electrovibration stimulus. However, there was a clear psychophysical masking effect due to central neural processes. Electrovibration absolute threshold increased approximately 0.19 dB for each dB increase in the masking level.

Realistic display of tactile textures on touch screens is a big step forward for haptic technology to reach a wide range of consumers utilizing electronic devices on a daily basis. Since the texture topography cannot be rendered explicitly by electrovibration on touch screens, it is important to understand how we perceive the virtual textures displayed by friction modulation via electrovibration. Here, we investigated the roughness perception of real gratings made of plexiglass and virtual gratings displayed by electrovibration through a touch screen for comparison. The results showed that the roughness perception of real and virtual gratings are different. We argue that this difference can be explained by the amount of fingerpad penetration into the gratings. For real gratings, penetration increased tangential forces acting on the finger, whereas for virtual ones where skin penetration is absent, tangential forces decreased with spatial period. 

Tactile Masking by Electrovibration

Future touch screen applications will include multiple tactile stimuli displayed simultaneously or consecutively to a single finger or multiple fingers. These applications should be designed by considering human tactile masking mechanism since it is known that presenting one stimulus may interfere with the perception of the other. Here, we investigate the effect of masking on tactile perception of electrovibration displayed on touch screens. Moreover, in order to investigate the effect of tactile masking on our haptic perception of edge sharpness, we compared the perceived sharpness of edges separating two textured regions displayed with and without various masking stimuli. Our results suggest that sharpness perception depends on the local contrast between background and foreground stimuli, which varies as a function of masking amplitude and activation levels of frequency-dependent psychophysical channels.

Effect of Waveform on Tactile Perception by Electrovibration Displayed on Touchscreens

Here, we investigated the effect of input voltage waveform on our haptic perception of electrovibration on touch screens. We found that the subjects were more sensitive to stimuli generated by square wave voltage than sinusoidal one for frequencies lower than 60 Hz. Using Matlab simulations, we showed that the sensation difference of waveforms in low fundamental frequencies occurred due to the frequency-dependent electrical properties of human skin and human tactile sensitivity. To validate our simulations, we actuated the touch screen at the threshold voltages and then measured the contact force and acceleration acting on the index fingers of the subjects moving on the screen with a constant speed. We analyzed the collected data in the frequency domain using the human vibrotactile sensitivity curve. The results suggested that Pacinian channel was the primary psychophysical channel in the detection of the electrovibration stimuli caused by all the square-wave inputs tested in this study.