Augmented eXperience and Interactive Systems Laboratory, Korea University. AXIS (Augmented experience and Interactive Systems) Lab focuses on developing core technologies and systems to enhance user experience (UX). We explore how humans and technology can interact more naturally and effectively. Our key objectives are to improve user experience with haptic technology, research next-generation VR, and design practical interfaces and applications.

Physical buttons provide clear haptic feedback when pressed and released, but their responses are unvarying. Physical buttons can be powered by force actuators to produce unlimited click sensations, but the cost is substantial. An alternative can be augmenting physical buttons with simple and inexpensive vibration actuators. When pushed, an augmented button generates a vibration overlayed on the button's original kinesthetic response, under the general framework of haptic augmented reality. We explore the design space of augmented buttons while changing vibration frequency, amplitude, duration, and envelope. We then visualize the perceptual structure of augmented buttons by estimating a perceptual space for 7 physical buttons and 40 augmented buttons. Their sensations are also assessed against adjectives, and results are mapped into the perceptual space to identify meaningful perceptual …

Augmenting physical buttons with vibrotactile feedback for programmable feels

This paper addresses the potential benefits of multimodal haptic feedback combining vibrotactile and impact stimuli for the target domain of virtual collision simulation. In this hybrid approach, we complement the limitation of each modality with the advantage of the other modality. We present the design of a hybrid device including both vibration and impact actuators and a physics-based rendering method for realistic collision simulation. We also report a user study carried out to comparatively assess the subjective quality of haptic collision rendering using vibration only, impact only, and multimodal (vibration + impact) stimuli. Experimental results demonstrate that our multimodal approach can contribute to critically expanding the dynamic range of virtual collision simulation, especially between highly stiff objects.

Realistic haptic rendering of collision effects using multimodal vibrotactile and impact feedback

In tactile interaction, a phantom sensation refers to an illusion felt on the skin between two distant points at which vibrations are applied. It can improve the perceptual spatial resolution of tactile stimulation with a few tactors. All phantom sensations reported in the literature act on the skin or out of the body, but no such reports exist for those eliciting sensations penetrating the body. This paper addresses tactile phantom sensations in which two vibration actuators on the dorsal and palmar sides of the hand present an illusion of vibration passing through the hand. We also demonstrate similar tactile illusions for the torso. For optimal design, we conducted user studies while varying vibration frequency, envelope function, stimulus duration, and penetrating direction. Based on the results, we present design guidelines on penetrating phantom sensations for its use in immersive virtual reality applications.

Body-penetrating tactile phantom sensations

With the recent progress of stretchable electronics, artificial tactile sensors pursue to imitate the human tactile system that is deformable and omnidirectional without signal interference. Although deformable tactile sensors without signal interference are demonstrated previously by using stretchable transistors or diodes, achieving omnidirectional tactility is very limited. It is because covering the 3D surfaces of fingers and hands with a sensor requests the structural simplicity and the customized shape design of the sensor. Here, a simple piezoresistive sensor without using the transistors or diodes is developed. The sensor is based on the localized piezoresistivity realized by creating the elastic resistive pixels that are laterally insulating with neighboring pixels. It can be wrapped on a finger and provide the pressure profiles and the spatial deformation of the substrate when multiple mechanical stimuli are applied from …

Omnidirectional tactile profiling using a deformable pressure sensor array based on localized piezoresistivity

One can embed a vibration actuator to a physical button and augment the physical button’s original kinesthetic response with a programmable vibration generated by the actuator. Such vibration-augmented buttons inherit the advantages of both physical and virtual buttons. This paper reports the information transmission capacity of vibration-augmented buttons. It was obtained by conducting a series of absolute identification experiments while increasing the number of augmented buttons. The information transmission capacity found was 2.6 bits, and vibration-augmented and physical buttons showed similar abilities in rendering easily recognizable haptic responses. In addition, we showcase a VR text entry application that utilizes vibration-augmented buttons. Our method provides several error messages to the user during text entry using a VR controller that includes an augmented button. We validate that the …

Vibration-augmented buttons: Information transmission capacity and application to interaction design

We present VibEye: a vibration-mediated recognition system of objects for tangible interaction. A user holds an object between two fingers wearing VibEye. VibEye triggers a vibration from one finger, and the vibration that has propagated through the object is sensed at the other finger. This vibration includes information about the object's identity, and we represent it using a spectrogram. Collecting the spectrograms of many objects, we formulate the object recognition problem to a classical classification problem among the images. This simple method, when tested with 20 users, shows 92.5% accuracy for 16 objects of the same shape with various materials. This material-based classifier is also extended to the recognition of everyday objects. Lastly, we demonstrate several tangible applications where VibEye provides the needed functionality while enhancing user experiences. VibEye is particularly effective for …

VibEye: Vibration-mediated object recognition for tangible interactive applications

An array of shear sensors is essential in tactile sensation as well as the pressure sensors. Surprisingly, however, the shear sensor array is rarely investigated mainly due to the structural complexity to measure the horizontal forces from various directions and also due to the mechanical softness required for preventing the slip of an object. Here, an array of small shear sensors that can recognize both shear force and shear rotational angle is fabricated. All the device components are made of deformable materials to acquire the softness of the sensor. This work presents a novel design for the small‐sized shear sensor array and the required material conditions for the design. By using an ion gel as the capacitive sensing material, the shear sensor array shows high sensitivity and excellent reliability under repeated shear forces. This work demonstrates playing computer game with the shear sensor and sensing the …

Small‐Sized Deformable Shear Sensor Array for Direct Monitoring of Quantitative Shear Distribution

The association of color and sound helps human cognition through a synergetic effect like intersensory facilitation. Although soft human‐machine interfaces (HMIs) providing unisensory expression have been widely developed, achieving synchronized optic and acoustic expression in one device system has been relatively less explored. It is because their operating principles are different in terms of materials, and implementation has mainly been attempted through structural approaches. Here, a deformable sound display is developed that generates multiple colored lights with large sound at low input voltage. The device is based on alternating‐current electroluminescence (ACEL) covered with perovskite composite films. A sound wave is created by a polymer matrix of the ACEL, while simultaneously, various colors are produced by the perovskite films and the blue electroluminescence (EL) emitted from the …

Interactive deformable colored sound display achieved with electrostrictive fluoropolymer and halide perovskite

Multimodal haptic rendering that simultaneously presents stimuli of multiple haptic modalities, such as vibration, impact, and thermal, has the potential to provide richer and more immersive haptic experiences than unimodal haptic rendering. For that, maintaining the synchrony between distinct haptic stimuli is crucial, as it significantly affects the overall quality of haptic sensations perceived by the user. In this paper, we investigate the perceptual sensitivity to the simultaneity between multimodal haptic stimuli combining impact and vibration. We design a handheld multimodal haptic device and conduct a perceptual experiment to measure the thresholds of perceived simultaneity between the two modalities while varying the vibration frequency and duration. Our results show that the order of two tactile stimuli for simultaneity perception is affected by both vibration frequency and duration. Specific results about the …

Perceptual simultaneity between vibrotactile and impact stimuli

This paper presents an experimental study on the fundamental human recognition performance of spatial tactile patterns applied on the torso. The patterns are made by either activating or deactivating four vibration actuators fastened to the body surface in a rectangular shape. Three body areas are considered for stimulation: the torso’s front (chest and stomach), back, and waist. A perceptual experiment shows that the human recognition accuracy of the spatial tactile patterns is high on the torso, over 91%. The accuracy depends on the stimulated body area and the number of simultaneously activated vibrations. In addition, the estimated information transfer ranges from 3.48 bits to 3.66 bits, indicating that the torso can transmit 11-12 spatial patterns without errors. These results can contribute to designing spatial tactile patterns that are effective for recently emerging haptic vests.

Human recognition performance of simple spatial vibrotactile patterns on the torso

We present a visuo-haptic crossmodal model of shape perception designed for shape-changing handheld controllers. The model uses the inertia tensor of an object to bridge the two senses. The model was constructed from the results of three perceptual experiments. In the first two experiments, we validate that the primary moment and product of inertia (MOI and POI) in the inertia tensor have critical effects on the haptic perception of object length and asymmetry. Then, we estimate a haptic-to-visual shape matching model using MOI and POI as two link variables from the results of the third experiment for crossmodal magnitude production. Finally, we validate in a summative user study that the inverse of the shape matching model is effective for pairing a perceptually-congruent haptic object from a virtual object—the functionality we need for shape-changing handheld interfaces to afford perceptually-fulfilling sensory …

Visuo-haptic crossmodal shape perception model for shape-changing handheld controllers bridged by inertial tensor

As computing paradigms shift toward mobile and ubiquitous interaction, there is an increasing demand for wearable interfaces supporting multifaceted input in smart living environments. In this regard, we introduce a system that identifies contact fingers using vibration as a modality of communication. We investigate the vibration characteristics of the communication channels involved and simulate the transmission of vibration sequences. In the simulation, we test and refine modulation and demodulation methods to design vibratory communication protocols that are robust to environmental noises and can detect multiple simultaneous contact fingers. As a result, we encode an on-off keying sequence with a unique carrier frequency to each finger and demodulate the sequences by applying cross-correlation. We verify the communication protocols in two environments, laboratory and cafe, where the resulting highest …

Identifying Contact Fingers on Touch Sensitive Surfaces by Ring-Based Vibratory Communication

We study whether the vibrotactile and thermal senses are independent in terms of information transmission. In Exp. 1, we estimated the respective information transmission capacities of vibrotactile and thermal stimuli. In Exp. 2, we measured the information transfer (IT) of vibrotactile-thermal multimodal stimuli. We compare the IT values obtained in the two experiments and demonstrate that approximately 90% of the information encoded through the two sensory modalities is preserved when they are combined. This result can contribute to the design of multimodal haptic stimuli for various user-interactive purposes.

A preliminary study on the perceptual independence between vibrotactile and thermal senses

Typical handheld controllers for interaction in virtual reality (VR) have fixed shapes and sizes, regardless of what visual objects they represent. Resolving this crossmodal incongruence with a shape-changing interface is our long-term goal. In this paper, we seek to find a length perception model that considers the moment of inertia (MOI) and diameter of a handheld object based on the concept of dynamic touch. Such models serve as a basis for computational algorithms for shape changing. We carried out two perceptual experiments. In Experiment 1, we measured the perceived lengths of 24 physical objects with different MOIs and diameters. Then we obtained a length perception model to reproduce the desired perceived length with a handheld controller. In Experiment 2, we validated our model in a crossmodal matching scenario, where a visual rod was matched to a haptic rod in terms of the perceived length …

Length perception model for handheld controllers: the effects of diameter and inertia

In the realm of virtual reality (VR), shape-changing controllers have emerged as a means to enhance visuo-haptic congruence during user interactions. The major emphasis has been placed on manipulating the inertia tensor of a shape-changing controller to control the perceived shape. This paper delves deeper by exploring how the material properties of the controller’s handle, distinct from the inertial information, affect the perceived shape, focusing on the perceived length. We conducted three perceptual experiments to examine the effects of the handle’s softness, thermal conductivity, and texture, respectively. Results demonstrated that a softer handle increases the perceived length, whereas a handle with higher thermal conductivity reduces it. Texture, in the form of varying bumps, also alters the length perception. These results provide more comprehensive knowledge of the intricate relationship between …

Augmenting Perceived Length of Handheld Controllers: Effects of Object Handle Properties

VBand: Implementation of Collaborative VR Band System with Haptic

Full-body vibrotactile stimuli are a promising means by which haptic interaction designers can substantially increase information transfer (IT). This paper reports the IT values of full-body sequential vibrotactile stimuli applied to ten body sites. We designed 10, 100, and 1,000 stimuli by increasing the number of vibrations in a sequence from one to three and estimated IT for each condition. We also obtained the lower and upper bounds of the IT estimates using several empirical methods to compensate for their biases. The IT estimate for each condition was 3.32, 6.55, and 8.05 bits, the highest IT ever reported in the haptics literature. This study is the first attempt to quantity the IT of full-body vibrotactile sequences, providing guidelines for the design of effective full-body vibrotactile stimuli.

Information transfer of full-body vibrotactile stimuli: an initial study with one to three sequential vibrations

Vibration and Impact Haptic Feedback for Realistic Collision Effect

This study investigates the human recognition performance of vibrotactile stimuli applied on the torso along azimuth or elevation under the context of tactile egocentric directional cueing. We conducted two absolute identification experiments for azimuth and elevation, respectively, using real tactile stimuli generated by physical actuators and illusory stimuli rendered by funneling illusion. For both azimuth and elevation, the recognition accuracies were very high, over 95.6%, when only real stimuli were used to indicate 6–8 directions. However, combining the real stimuli with the illusory ones to double the spatial resolution resulted in significantly lower accuracies between 74.1% and 77.8%. The estimated information transfer (IT) values also remained very similar. Using identical methods, our results quantify the human identification performance of torso-distributed tactile stimuli for azimuth or elevation. The detailed …

Human identification performance of vibrotactile stimuli applied on the torso along azimuth or elevation

Deformable touch sensors with a high spatiotemporal resolution have recently attracted significant attention as a promising option for electronic skin and human‐machine interfaces. However, the conventional electronic matrix arrays require a large number of addressing lines and suffer from response time delay. In this study, a novel mechanically robust elastic electronic touch sensor is reported featuring only a limited number (2 or 4) of signal terminals. The sensor has a simple structure comprising an elastic spacer and two substrates with a conductive electrode of uniform resistance along the entire length of the electrode. By decoding the temporal resistance profiles from the touch sensor by using a simple simulator, the sensor can provide precise touch information such as position, instant moving speed and direction, and the trajectories of the movements. The touch actions are displayed in real‐time, regardless …

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HaRing: A Haptic Ring Interface for One-Handed Interaction with High-Dimensional Spatial Information

Effects of Haptic Feedback on Gaming Experiences: A Case Study Comparing Players and Spectators in FPS Games

Effects of Spatiotemporal Parameters on Forearm Vibrotactile Stimulus Identification

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