Ultrasonic mid-air haptics (UMH) offers a novel way to modulate affective responses through contactless, biosignal features inspired haptics (i.e., BioHaptics). Yet, the effects of different BioHaptics on affective responses of emotions experienced during video-watching context are unclear, limiting the flexible emotion modulation and broader use of UMH as a natural affective design channel in enhancing everyday media consumption. This paper explores how BioHaptics encoded from different biosignal features (e.g., heart rate (HR), heart rate variability (HRV), and respiration amplitude (RA)) impact emotions in video-watching contexts. In two experiments with 70 participants, we assessed affective responses while adding three BioHaptics during the video-watching processes. Results showed that HR and RA haptics promoted RA and HRV, with potential increments in emotional pleasantness and regulation; HRV haptics lowered HR, leading to calmer responses. This research offers implications and recommendations for emotion modulation through UMH and advances the design of emotionally engaging multisensory feedback.

Acoustic levitation enables mid-air displays using physical particles to create 3D visuals, but stability limits the achievable animation complexity. Stability depends on factors including the acoustic solver, particle count, motion speed, and path geometry. This paper analyzes these factors, characterizing their effects, identifying constraints, and allowing particles to successfully follow the paths. We then propose Acoustic Actor-Critic (AAC), a closed-loop motion planning system that maximizes stability for multi-particle trajectories with minimal changes to the intended visual content. This follows a plan-detect-repair strategy: i) the Actor plans trajectories under the established constraints; ii) the Critic evaluates their stability and detects instabilities; iii) the Repair modules trigger localized repairs upon unstable path segments. Results showed that AAC can automatically refine and repair multi-particle trajectories, reducing failures from 21% to 6% across 100 paths. Our findings enable creators to produce more stable levitation paths, while AAC automatically refines trajectories with minimal deviation from the original animations.

Decision Transformers (DTs) effectively capture long-range dependencies using self-attention but struggle with fine-grained local relationships, especially the Markovian properties in many offline-RL datasets. Conversely, Decision Convformer (DC) utilizes convolutional filters for capturing local patterns but shows limitations in tasks demanding long-term dependencies, such as Maze2d. To address these limitations and leverage both strengths, we propose the Long-Short Decision Transformer (LSDT), a general-purpose architecture to effectively capture global and local dependencies across two specialized parallel branches (self-attention and convolution). We explore how these branches complement each other by modeling various ranged dependencies across different environments, and compare it against other baselines. Experimental results demonstrate our LSDT achieves state-of-the-art performance and notable gains over the standard DT in D4RL offline RL benchmark. Leveraging the parallel architecture, LSDT performs consistently on diverse datasets, including Markovian and non-Markovian. We also demonstrate the flexibility of LSDT's architecture, where its specialized branches can be replaced or integrated into models like DC to improve their performance in capturing diverse dependencies. Finally, we also highlight the role of goal states in improving decision-making for goal-reaching tasks like Antmaze.

Cooperative transport, the simultaneous movement of an object by multiple agents, has been widely observed in biological systems such as ant colonies, which improve efficiency and adaptability in dynamic environments. Inspired by these natural phenomena, we present a novel acoustic robotic system for the transport of contactless objects in mid-air. Our system utilizes onboard phased ultrasonic transducers and a robotic control system to generate localized acoustic pressure fields, enabling the precise manipulation of airborne particles and robots. We categorize contactless object-transport strategies into independent transport (uncoordinated) and forward-facing cooperative transport (coordinated), drawing parallels with biological systems to optimize efficiency and robustness. The proposed system is experimentally validated by evaluating levitation stability using a microphone in the measurements lab, transport efficiency through a phase-space motion capture system, and clock synchronization accuracy using an oscilloscope. The results demonstrate the feasibility of both independent and cooperative airborne object transport. This research contributes to the field of acoustophoretic robotics, with potential applications in contactless material handling, microassembly, and biomedical applications.

Perceived Continuity CRE f) FE STM CRE FE STM a) 1 2 3 3 4 c) b) d) Figure 1: a) Different sensitivity areas across the hand overlaid with pacinian receptors (dots).We create tactile shapes at low (c) and high (b) sensitivity areas, as well as across areas (d and e), comparing their perceived intensity and continuity when using spatiotemporal modulation (STM) and tactile illusions (funneling effect (FE) and cutaneous rabbit effect (CRE) ) (f).

Multi-point STM offers a great range of parameters (i.e., drawing frequency, number of points) to produce different tactile sensations. However, existing studies offer limited insight on the effects of these parameters, and ignore their effect on the physical stimuli delivered, limiting effective haptic design. We propose a two-stage model to predict response to multi-point STM. The first stage predicts physical stimulus properties with 7.8% error, while the second stage predicts mean and spread of perceived intensity with 8.0 % and 8.8% error. We report 3 studies conducted to derive this model: one to characterize physical stimuli, another one measuring user perceptual thresholds, and a third one measuring user’s perceptual response to multi-point STM. Besides, we characterize 4 effects that influence device performance, confirm if previous effects reported are due to physical or perceptual effects (or both) and derive recommendations for manufacturers, haptic designers and HCI researchers.

Data physicalisation is a technique that encodes data through the geometric and material properties of an artefact, allowing users to engage with data in a more immersive and multi-sensory way. However, current methods of data physicalisation are limited in terms of their reconfigurability and the types of materials that can be used. Acoustophoresis—a method of suspending and manipulating materials using sound waves—offers a promising solution to these challenges. In this paper, we present DataLev, a design space and platform for creating reconfigurable, multimodal data physicalisations with enriched materiality using acoustophoresis. We demonstrate the capabilities of DataLev through eight examples and evaluate its performance in terms of reconfigurability and materiality. Our work offers a new approach to data physicalisation, enabling designers to create more dynamic, engaging, and expressive artefacts.

Spatiotemporal modulation (STM) is used to render tactile patterns with ultrasound arrays. Previous research only explored the effects of single-point STM parameters, such as drawing speed (Vd). Here we explore the effects of multi-point STM on both perceptual (intensity) and emotional (valence/arousal) responses. This introduces a new control parameter for STM - the number of focal points (Nfp) – on top of conventional STM parameter (Vd). Our results from a study with 30 participants showed a negative effect of Nfp on perceived intensity and arousal, but no significant effects on valence. We also found the effects of Vd still aligned with prior results for single-point, even when different Nfp were used, suggesting that effects observed from single-point also apply to multi-point STM. We finally derive recommendations, such as using single-point STM to produce stimuli with higher intensity and/or arousal, or using multi-point STM for milder and more relaxing (less arousing) experiences.

Phased arrays of transducers have been quickly evolving in terms of software and hardware with applications in haptics (acoustic vibrations), display (levitation), and audio. Most recently, Multimodal Particle-based Displays (MPDs) have even demonstrated volumetric content that can be seen, heard, and felt simultaneously, without additional instrumentation. However, current software tools only support individual modalities and they do not address the integration and exploitation of the multi-modal potential of MPDs. This is because there is no standardized presentation pipeline tackling the challenges related to presenting such kind of multi-modal content (e.g., multi-modal support, multi-rate synchronization at 10 KHz, visual rendering or synchronization and continuity). This article presents OpenMPD, a low-level presentation engine that deals with these challenges and allows structured exploitation of any type of MPD content (i.e., visual, tactile, audio). We characterize OpenMPD’s performance and illustrate how it can be integrated into higher-level development tools (i.e., Unity game engine). We then illustrate its ability to enable novel presentation capabilities, such as support of multiple MPD contents, dexterous manipulations of fast-moving particles, or novel swept-volume MPD content.

Acoustic levitation has emerged as a promising approach for mid-air displays, by using multiple levitated particles as 3D voxels, cloth and thread props, or high-speed tracer particles, under the promise of creating 3D displays that users can see, hear and feel with their bare eyes, ears and hands. However, interaction with this mid-air content always occurred at a distance, since external objects in the display volume (e.g. user’s hands) can disturb the acoustic fields and make the particles fall. This paper proposes TipTrap, a co-located direct manipulation technique for acoustically levitated particles. TipTrap leverages the reflection of ultrasound on the users’ skin and employs a closed-loop system to create functional acoustic traps 2.1 mm below the fingertips, and addresses its 3 basic stages: selection, manipulation and deselection. We use Finite-Differences Time Domain (FDTD) simulations to explain the principles enabling TipTrap, and explore how finger reflections and user strategies influence the quality of the traps (e.g. approaching direction, orientation and tracking errors), and use these results to design our technique. We then implement the technique, characterizing its performance with a robotic hand setup and finish with an exploration of the ability of TipTrap to manipulate different types of levitated content.

Acoustic levitation has recently demonstrated the ability to create volumetric content by trapping and quickly moving particles along reference paths to reveal shapes in mid-air. However, the problem of specifying physically feasible trap trajectories to display desired shapes remains unsolved. Even if only the final shape is of interest to the content creator, the trap trajectories need to determine where and when the traps need to be, for the particle to reveal the intended shape. We propose OptiTrap , the first structured numerical approach to compute trap trajectories for acoustic levitation displays. Our approach generates trap trajectories that are physically feasible and nearly time-optimal, and reveal generic mid-air shapes, given only a reference path (i.e., a shape with no time information). We provide a multi-dimensional model of the acoustic forces around a trap to model the trap-particle system dynamics and compute optimal trap trajectories by formulating and solving a non-linear path following problem. We formulate our approach and evaluate it, demonstrating how OptiTrap consistently produces feasible and nearly optimal paths, with increases in size, frequency, and accuracy of the shapes rendered, allowing us to demonstrate larger and more complex shapes than ever shown to date.

Acoustic levitation is gaining popularity as an approach to create physicalized mid-air content by levitating different types of levitation primitives. Such primitives can be independent particles or particles that are physically connected via threads or pieces of cloth to form shapes in mid-air. However, initialization (i.e., placement of such primitives in their mid-air target locations) currently relies on either manual placement or specialized ad-hoc implementations, which limits their practical usage. We present ArticuLev, an integrated pipeline that deals with the identification, assembly and mid-air placement of levitated shape primitives. We designed ArticuLev with the physical properties of commonly used levitation primitives in mind. It enables experiences that seamlessly combine different primitives into meaningful structures (including fully articulated animated shapes) and supports various levitation display approaches (e.g., particles moving at high speed). In this paper, we describe our pipeline and demonstrate it with heterogeneous combinations of levitation primitives.

This paper presents a thin digital full-face mask display that can reflect an entire facial expression of a user onto an avatar to support augmented face-to-face communication in real environments. Although camera-based facial expression recognition technology has enabled people to augment their faces with avatars, application was limited to face-to-face communication in virtual environments. To enable digital facial augmentation with an avatar in a real space, we propose a digital face mask display system that integrates a lightweight flexible display with a thin facial expression recognition system. The thin wearable facial expression recognition system was implemented with photo reflective sensor arrays which can measure facial expressions at 40 feature points distributed across an entire face. We investigated a ten-class facial expression identification model based on an SVM training algorithm. The trained model achieved an average accuracy of 79% when identifying the facial expressions of multiple users. User experiments indicated that the proposed thin digital full-face mask display allows the wearer to control the facial expression of the avatar with a fast response rate and create a positive sense of self-agency and self-ownership toward the augmented avatar face.

3D selection in dense VR environments (e.g., point clouds) is extremely challenging due to occlusion and imprecise mid-air input modalities (e.g., 3D controllers and hand gestures). In this paper, we propose "Slicing-Volume", a hybrid selection technique that enables simultaneous 3D interaction in mid-air, and a 2D pen-and-tablet metaphor in VR. Inspired by well-known slicing plane techniques in data visualization, our technique consists of a 3D volume that encloses target objects in mid-air, which are then projected to a 2D tablet view for precise selection on a tangible physical surface. While slicing techniques and tablets-in-VR have been previously explored, in this paper, we evaluated the potential of this hybrid approach to improve accuracy in highly occluded selection tasks, comparing different multimodal interactions (e.g., Mid-air, Virtual Tablet and Real Tablet). Our results showed that our hybrid technique significantly improved overall accuracy of selection compared to Mid-air selection only, thanks to the added haptic feedback given by the physical tablet surface, rather than the added visualization given by the tablet view.

Phased Arrays of Transducers (PATs) allow accurate control of ultrasound fields, with applications in haptics, levitation (i.e. displays) and parametric audio. However, algorithms for multi-point levitation or tactile feedback are usually limited to computing solutions in the order of hundreds of sound-fields per second, preventing the use of multiple high-speed points, a feature that can broaden the scope of applications of PATs. We present GS-PAT , a GPU multi-point phase retrieval algorithm, capable of computing 17K solutions per second for up to 32 simultaneous points in a mid-end consumer grade GPU (NVidia GTX 1660). We describe the algorithm and compare it to state of the art multi-point algorithms used for ultrasound haptics and levitation, showing similar quality of the generated sound-fields, and much higher computation rates. We then illustrate how the shift in paradigm enabled by GS-PAT (i.e. real-time control of several high-speed points) opens new applications for PAT technologies, such as in volumetric fully coloured displays, multi-point spatio-temporal tactile feedback, parametric audio and simultaneous combinations of these modalities.

Permeable, mid-air displays, such as those using fog or water mist are limited by our ability to shape and control the aerosol and deal with two major issues: (1) the size and complexity of the system, and (2) the creation of laminar flow, to retain display quality. Here we present SonicSpray, a technique using ultrasonic Bessel beams to create reconfigurable mid-air displays. We build a prototype from low-cost, off-the-shelf parts. We explore the potential and limitations of SonicSpray to create and redirect laminar flows of fog. We demonstrate a working prototype that precisely controls laminar aerosols through only 6x6 ultrasound transducers array. We describe the implementation steps to build the device, verify the control and projection algorithm for the display, and evaluate its performance. We finally report our exploration of several useful applications, in learning, entertainment and arts.

LeviProps are tangible structures used to create interactive mid-air experiences. They are composed of an acoustically- transparent lightweight piece of fabric and attached beads that act as levitated anchors. This combination enables real- time 6 Degrees-of-Freedom control of levitated structures which are larger and more diverse than those possible with previous acoustic manipulation techniques. LeviProps can be used as free-form interactive elements and as projection surfaces. We developed an authoring tool to support the creation of LeviProps. Our tool considers the outline of the prop and the user constraints to compute the optimum locations for the anchors (i.e. maximizing trapping forces), increasing prop stability and maximum size. The tool produces a final LeviProp design which can be fabricated following a simple procedure. This paper explains and evaluates our approach and showcases example applications, such as interactive storytelling, games and mid-air displays.

Scale adaptive techniques for VR navigation enable users to navigate spaces larger than the real space available, while allowing precise interaction when required. However, due to these techniques gradually scaling displacements as the user moves (changing user's speed), they introduce a Drift effect. That is, a user returning to the same point in VR will not return to the same point in the real space. This mismatch between the real/virtual spaces can grow over time, and turn the techniques unusable (i.e., users cannot reach their target locations). In this paper, we characterise and analyse the effects of Drift, highlighting its potential detrimental effects. We then propose two techniques to correct Drift effects and use a data driven approach (using navigation data from real users with a specific scale adaptive technique) to tune them, compare their performance and chose an optimum correction technique and configuration. Our user study, applying our technique in a different environment and with two different scale adaptive navigation techniques, shows that our correction technique can significantly reduce Drift effects and extend the life-span of the navigation techniques (i.e., time that they can be used before Drift draws targets unreachable), while not hindering users' experience.

Ultrasound manipulation is growing in popularity in the HCI community with applications in haptics, on-body interaction, and levitation-based displays. Most of these applications share two key limitations: a) the complexity of the sound fields that can be produced is limited by the physical size of the transducers, and b) no obstacles can be present between the transducers and the control point. We present SoundBender, a hybrid system that overcomes these limitations by combining the versatility of phased arrays of Transducers (PATs) with the precision of acoustic metamaterials. In this paper, we explain our approach to design and implement such hybrid modulators (i.e. to create complex sound fields) and methods to manipulate the field dynamically (i.e. stretch, steer). We demonstrate our concept using self-bending beams enabling both levitation and tactile feedback around an obstacle and present example applications enabled by SoundBender.

We present MistForm, a shape changing fog display that can support one or two users interacting with either 2D or 3D content. Mistform combines affordances from both shape changing interfaces and mid-air displays. For example, a concave display can maintain content in comfortable reach for a single user, while a convex shape can support several users engaged on individual tasks. MistForm also enables unique interaction possibilities by exploiting the synergies between shape changing interfaces and mid-air fog displays. For instance, moving the screen will affect the brightness and blurriness of the screen at specific locations around the display, creating spaces with similar (collaboration) or different visibility (personalized content). We describe the design of MistForm and analyse its inherent challenges, such as image distortion and uneven brightness on dynamic curved surfaces. We provide a machine learning approach to characterize the shape of the screen and a rendering algorithm to remove aberrations. We finally explore novel interactive possibilities and reflect on their potential and limitations.

Virtual Reality allow users to explore virtual environments naturally, by moving their head and body. However, the size of the environments they can explore is limited by real world constraints, such as the tracking technology or the physical space available. Existing techniques removing these limitations often break the metaphor of natural navigation in VR (e.g. steering techniques), involve control commands (e.g., teleporting) or hinder precise navigation (e.g., scaling user's displacements). This paper proposes NaviFields, which quantify the requirements for precise navigation of each point of the environment, allowing natural navigation within relevant areas, while scaling users' displacements when travelling across non-relevant spaces. This expands the size of the navigable space, retains the natural navigation metaphor and still allows for areas with precise control of the virtual head. We present a formal description of our NaviFields technique, which we compared against two alternative solutions (i.e., homogeneous scaling and natural navigation). Our results demonstrate our ability to cover larger spaces, introduce minimal disruption when travelling across bigger distances and improve very significantly the precise control of the viewpoint inside relevant areas.

Interaction in VR involves large body movements, easily inducing fatigue and discomfort. We propose Erg-O, a manipulation technique that leverages visual dominance to maintain the visual location of the elements in VR, while making them accessible from more comfortable locations. Our solution works in an open-ended fashion (no prior knowledge of the object the user wants to touch), can be used with multiple objects, and still allows interaction with any other point within user's reach. We use optimization approaches to compute the best physical location to interact with each visual element, and space partitioning techniques to distort the visual and physical spaces based on those mappings and allow multi-object retargeting. In this paper we describe the Erg-O technique, propose two retargeting strategies and report the results from a user study on 3D selection under different conditions, elaborating on their potential and application to specific usage scenarios.

Current devices have limited battery life, typically lasting less than one day. This can lead to situations where critical tasks, such as making an emergency phone call, are not possible. Other devices, supporting different functionality, may have sufficient battery life to enable this task. We present PowerShake; an exploration of power as a shareable commodity between mobile (and wearable) devices. PowerShake enables users to control the balance of power levels in their own devices (intra-personal transactions) and to trade power with others (inter-personal transactions) according to their ongoing usage requirements. This paper demonstrates Wireless Power Transfer (WPT) between mobile devices. PowerShake is: simple to perform on-the-go; supports ongoing/continuous tasks (transferring at ~3.1W); fits in a small form factor; and is compliant with electromagnetic safety guidelines while providing charging efficiency similar to other standards (48.2% vs. 51.2% in Qi). Based on our proposed technical implementation, we run a series of workshops to derive candidate designs for PowerShake enabled devices and interactions, and to bring to light the social implications of power as a tradable asset.

The form factors of displays using fog or water surface are limited by our ability to control the non-solid substances used as the diffuser. We propose a charging technique for polar aerosols (e.g., mist or fog) that allows control of the shape and trajectory of such non-solid diffusers using electric fields. We report experiments that allowed us to design a charging mechanism that produces charged fog aerosols with homogeneous electrical mobility. We illustrate our idea by demonstrating how electric fields can be used to control the shape of a fog display and the trajectory of a bubble display.

We present MisTable, a tabletop system that combines a conventional horizontal interactive surface with personal screens between the user and the tabletop surface. These personal screens, built using fog, are both see-through and reach-through. Being see-through provides direct line of sight of the personal screen and the elements behind it on the tabletop. Being reach-through allows the user to switch from interacting with the personal screen to reaching through it to interact with the tabletop or the space above it. The personal screen allows a range of customisations and novel interactions such as presenting 2D personal contents on the screen, 3D contents above the tabletop or augmenting and relighting tangible objects differently for each user. Besides, having a personal screen for each user allows us to customize the view of each of them according to their identity or preferences. Finally, the personal screens preserve all well-established tabletop interaction techniques like touch and tangible interactions. We explore the challenges in building such a reach-through system through a proof-of-concept implementation and discuss the possibilities afforded by the system.

We present SensaBubble, a chrono-sensory mid-air display system that generates scented bubbles to deliver information to the user via a number of sensory modalities. The system reliably produces single bubbles of specific sizes along a directed path. Each bubble produced by SensaBubble is filled with fog containing a scent relevant to the notification. The chrono-sensory aspect of SensaBubble means that information is presented both temporally and multimodally. Temporal information is enabled through two forms of persistence: firstly, a visual display projected onto the bubble which only endures until it bursts; secondly, a scent released upon the bursting of the bubble slowly disperses and leaves a longer-lasting perceptible trace of the event. We report details of SensaBubble's design and implementation, as well as results of technical and user evaluations. We then discuss and demonstrate how SensaBubble can be adapted for use in a wide range of application contexts -- from an ambient peripheral display for persistent alerts, to an engaging display for gaming or education.

We present Portallax, a clip-on technology to retrofit mobile devices with 3D display capabilities. Available technologies (e.g. Nintendo 3DS or LG Optimus) and clip-on solutions (e.g. 3DeeSlide and Grilli3D) force users to have a fixed head and device positions. This is contradictory to the nature of a mobile scenario, and limits the usage of interaction techniques such as tilting the device to control a game. Portallax uses an actuated parallax barrier and face tracking to realign the barrier's position to the user's position. This allows us to provide stereo, motion parallax and perspective correction cues in 60 degrees in front of the device. Our optimized design of the barrier minimizes colour distortion, maximizes resolution and produces bigger view-zones, which support ~81% of adults' interpupillary distances and allow eye tracking implemented with the front camera. We present a reference implementation, evaluate its key features and provide example applications illustrating the potential of Portallax.

Reflective optical combiners like beam splitters and two way mirrors are used in AR to overlap digital contents on the users' hands or bodies. Augmentations are usually unidirectional, either reflecting virtual contents on the user's body (Situated Augmented Reality) or augmenting user's reflections with digital contents (AR mirrors). But many other novel possibilities remain unexplored. For example, users' hands, reflected inside a museum AR cabinet, can allow visitors to interact with the artifacts exhibited. Projecting on the user's hands as their reflection cuts through the objects can be used to reveal objects' internals. Augmentations from both sides are blended by the combiner, so they are consistently seen by any number of users, independently of their location or, even, the side of the combiner through which they are looking. This paper explores the potential of optical combiners to merge the space in front and behind them. We present this design space, identify novel augmentations/interaction opportunities and explore the design space using three prototypes.

We present PiVOT, a tabletop system aimed at supporting mixed-focus collaborative tasks. Through two view-zones, PiVOT provides personalized views to individual users while presenting an unaffected and unobstructed shared view to all users. The system supports multiple personalized views which can be present at the same spatial location and yet be only visible to the users it belongs to. The system also allows the creation of personal views that can be either 2D or (auto-stereoscopic) 3D images. We first discuss the motivation and the different implementation principles required for realizing such a system, before exploring different designs able to address the seemingly opposing challenges of shared and personalized views. We then implement and evaluate a sample prototype to validate our design ideas and present a set of sample applications to demonstrate the utility of the system.

In this paper a study is conducted in order to evaluate three different strategies of haptic feedback for texture discrimination in virtual environments. Specifically, both force and vibrotactile feedback have been evaluated, as well as the direct use of the sense of touch, to detect different textures. To this end, a force feedback Phantom device, a custom built vibrotactile data glove and paper palpable prototypes, which represent an ideal model of tactile feedback, have been compared. These three methods have been used to detect two types of patterns, one formed by different geometrical shapes, and the other with different grooves width. Results show that the vibrotactile data glove has a notable behaviour in the detection of textures where the frequency of tactile stimuli varies, and it is even useful to detect more complex textures.

This paper analyses the Spatial Model of Interaction, a model that rules the possible interactions among two objects and that has been widely accepted and used in many CVE systems. As a result of this analysis, some deficiencies are revealed and a new model of interaction is proposed. Additionally, a prototype illustrating some of the best features of this model of interaction is detailed.

In the research community, developers of Collaborative Virtual Environments (CVEs) usually refer to the terms awareness and feedback as something necessary to maintain a fluent collaboration when highly interactive tasks have to be performed. However, it is remarkable that few studies address the effect that including special kinds of feedback has on user awareness and task performance. This work follows a preliminary experiment where we already studied awareness in CVEs, evaluating the effect of visual cues in the performance of collaborative tasks and showing that users tend to make more mistakes when such feedback is not provided, that is, they are less aware. These early results were promising and encouraged us to continue investigating the benefit of improving awareness in tasks that require close collaboration between users, but this time analyzing more types of awareness and experimenting with visual, audio and vibrotactile feedback cues.

The development of 3D user interfaces is mostly focused on technology and the ways of using it, and so the main concerns are the selection of hardware, software and interaction techniques. The process of development itself is as important as these issues, but it is usually ignored or poorly documented. This paper introduces the TRES-D methodology, and illustrates its application in the development of three different glove-based interfaces, not only to show the benefits of using these devices, but also the benefits of using such a methodological framework.