Multimodal Interfaces (MMIs) combining speech and spatial input have the potential to elicit minimal cognitive load. Low cognitive load increases effectiveness as well as user satisfaction and is regarded as an important aspect of intuitive use. While this potential has been extensively theorized in the research community, experiments that provide supporting observations based on functional interfaces are still scarce. In particular, there is a lack of studies comparing the commonly used Unimodal Interfaces (UMIs) with theoretically superior synergistic MMI alternatives. Yet, these studies are an essential prerequisite for generalizing results, developing practice-oriented guidelines, and ultimately exploiting the potential of MMIs in a broader range of applications. This work contributes a novel observation towards the resolution of this shortcoming in the context of the following combination of applied interaction techniques, tasks, application domain, and technology: We present a comprehensive evaluation of a synergistic speech & touch MMI and a touch-only menu-based UMI (interaction techniques) for selection and system control tasks in a digital tabletop game (application domain) on an interactive surface (technology). Cognitive load, user experience, and intuitive use are evaluated, with the former being assessed by means of the dual-task paradigm. Our experiment shows that the implemented MMI causes significantly less cognitive load and is perceived significantly more usable and intuitive than the UMI. Based on our results, we derive recommendations for the interface design of digital tabletop games on interactive surfaces. Further, we argue that our results and design recommendations are suitable to be generalized to other application domains on interactive surfaces for selection and system control tasks.

Multimodal Interfaces (MMIs) have been considered to provide promising interaction paradigms for Virtual Reality (VR) for some time. However, they are still far less common than unimodal interfaces (UMIs). This paper presents a summative user study comparing an MMI to a typical UMI for a design task in VR. We developed an application targeting creative 3D object manipulations, i.e., creating 3D objects and modifying typical object properties such as color or size. The associated open user task is based on the Torrence Tests of Creative Thinking. We compared a synergistic multimodal interface using speech-accompanied pointing/grabbing gestures with a more typical unimodal interface using a hierarchical radial menu to trigger actions on selected objects. Independent judges rated the creativity of the resulting products using the Consensual Assessment Technique. Additionally, we measured the creativity-promoting factors flow, usability, and presence. Our results show that the MMI performs on par with the UMI in all measurements despite its limited flexibility and reliability. These promising results demonstrate the technological maturity of MMIs and their potential to extend traditional interaction techniques in VR efficiently.

This paper introduces a method for computing the difficulty of selection tasks in virtual environments using pointing metaphors by operationalizing an established human motor behavior model. In contrast to previous work, the difficulty is calculated automatically at run-time for arbitrary environments. We present and provide the implementation of our method within Unity 3D. The difficulty is computed based on a contextual analysis of spatial boundary conditions, i.e., target object size and shape, distance to the user, and occlusion. We believe our method will enable developers to build adaptive systems that automatically equip the user with the most appropriate selection technique according to the context. Further, it provides a standard metric to better evaluate and compare different selection techniques.

Biometric measures such as the electroencephalogram (EEG) promise to become viable alternatives to subjective questionnaire ratings for the evaluation of psychophysical effects associated with Virtual Reality (VR) systems, as they provide objective and continuous measurements without breaking the exposure. The extent to which the EEG signal can be disturbed by the presence of VR systems, however, has been barely investigated. This study outlines how to evaluate the compatibility of a given EEG-VR setup on the example of two commercial head-mounted displays (HMDs), the Oculus Rift and the HTC Vive Pro. We use a novel experimental protocol to compare the spectral composition between conditions with and without an HMD present during an eyes-open vs. eyes-closed task. We found general artifacts at the line hum of 50 Hz, and additional HMD refresh rate artifacts (90 Hz) for the Oculus rift exclusively. Frequency components typically most interesting to non-invasive EEG research and applications , however, remained largely unaffected. We observed similar topographies of visually-induced modulation of alpha band power for both HMD conditions in all subjects. Hence, the study introduces a necessary validation test for HMDs in combination with EEG and further promotes EEG as a potential biometric measurement method for psychophysical effects in VR systems.

Multimodal interfaces for Virtual Reality (VR), e.g., based on speech and gesture input/output (I/O), often exhibit complex system architectures. Tight couplings between the required I/O processing stages and the underlying scene representation and the simulator system's flow-of-control tend to result in high development and maintainability costs. This paper presents a maintainable solution for realizing such interfaces by means of a cherry-picking approach. A reusable multimodal I/O processing platform is combined with the simulation and rendering capabilities of the Unity game engine, allowing to exploit the game engine's superior API usability and tool support. The approach is illustrated based on the development of a multimodal VR adventure game called Space Tentacles.

Modularity, modifiability, reusability, and API usability are important software qualities that determine the maintainability of software architectures. Virtual, Augmented, and Mixed Reality (VR, AR, MR) systems, modern computer games, as well as interactive human-robot systems often include various dedicated input-, output-, and processing subsystems. These subsystems collectively maintain a real-time simulation of a coherent application state. The resulting interdependencies between individual state representations, mutual state access, overall synchronization, and flow of control implies a conceptual close coupling whereas software quality asks for a decoupling to develop maintainable solutions. This article presents five semantics-based software techniques that address this contradiction: Semantic grounding, code from semantics, grounded actions, semantic queries, and decoupling by semantics. These techniques are applied to extend the well-established entity-component-system (ECS) pattern to overcome some of this pattern's deficits with respect to the implied state access. A walk-through of central implementation aspects of a multimodal (speech and gesture) VR-interface is used to highlight the techniques' benefits. This use-case is chosen as a prototypical example of complex architectures with multiple interacting subsystems found in many VR, AR and MR architectures. Finally, implementation hints are given, lessons learned regarding maintainability pointed-out, and performance implications discussed.

This paper presents a mixed reality tabletop role-playing game with a novel combination of interaction styles and gameplay mechanics. Our contribution extends previous approaches by abandoning the traditional turn-based gameplay in favor of simultaneous real-time interaction. The increased cognitive and physical load during the simultaneous control of multiple game characters is counteracted by two features: First, certain game characters are equipped with AI-driven capabilities to become semi-autonomous virtual agents. Second, (groups of) these agents can be instructed by high-level commands via a multimodal - speech and gesture - interface.

We present four raycast-based techniques that determine the transformation between a depth camera's coordinate system and the coordinate system defined by a rectangular surface. In addition, the surface's dimensions are measured. In contrast to other approaches, these techniques limit additional hardware requirements to commonly available, low-cost artifacts and focus on simple non-laborious procedures. A preliminary study examining our Kinect v2-based proof of concept revealed promising first results. The utilized software is available as an open-source project.

This paper introduces an interactive surface concept for Mixed Reality (MR) tabletop games that combines a variable (LCD and/or projection) screen configuration with the detection of finger touches, in-air gestures, and tangibles. It is low-cost and minimally requires an ordinary table, a TV screen, and a Kinect v2 sensor. Existing applications can easily be connected by being compliant to standards. The concept is intended to foster further research on collaborative tabletop situations, not limited to games, but also including learning, meetings, and social interaction.

This poster presents a maintainable method to manage lexical information required for multimodal interfaces. It is tailored for the application in real-time interactive systems, specifically for Virtual Reality, and solves three problems commonly encountered in this context: (1) The lexical information is defined on and grounded in a common knowledge representation layer (KRL) based on OWL. The KRL describes application objects and possible system functions in one place and avoids error-prone redundant data management. (2) The KRL is tightly integrated into the simulator platform using a semantically enriched object model that is auto-generated from the KRL and thus fosters high performance access. (3) A well-defined interface provides application wide access to semantic application state information in general and the lexical information in specific, which greatly contributes to decoupling, maintainability, and reusability.

Multimodal interaction frameworks are an efficient means of utilizing many existing processing and fusion techniques in a wide variety of application areas, even by non-experts. However, the application of these frameworks to highly interactive application areas like VR, AR, MR, and computer games in a reusable, modifiable, and modular manner is not straightforward. It currently lacks some software technical solutions that (1) preserve the general decoupling principle of platforms and at the same time (2) provide the required close temporal as well as semantic coupling of involved software modules and multimodal processing steps. This thesis approches current challenges and aims at providing the research community with a framework that fosters repeatability of scientific achievements and the ability to built on previous results.

Quest — XRoads is a multimodal and multimedia mixed reality version of the traditional role-play tabletop game Quest: Zeit der Helden. The original game concept is augmented with virtual content to permit a novel gaming experience. The demonstration consists of a turn-based skirmish, where players have to collaborate, control heroes or villains and use their abilities via speech, gesture, touch as well as tangible interactions.

This article evaluates the utility of three technical design approaches implemented during the development of a Realtime Interactive Systems (RIS) architecture focusing on the areas of Virtual and Augmented Reality (VR and AR), Robotics, and Human-Computer Interaction (HCI). The design decisions are (1) the choice of the Scala programming language, (2) the implementation of the actor computational model, and (3) the central incorporation of ontologies as a base for semantic modeling, required for several Artificial Intelligence (AI) methods. A white-box expert review is applied to a detailed use case illustrating an interactive and multimodal game scenario, which requires a number of complex functional features like speech and gesture processing and instruction mapping. The review matches the three design decisions against three comprehensive non-functional requirements from software engineering: Reusability, scalability, and extensibility. The qualitative evaluation is condensed to a semi-quantitative summary, pointing out the benefits of the chosen technical design.

We present SiXton 's Curse-a computer game-to illustrate the ben efits of a novel simulation platform. Simulator X [2] targets vir tual, augmented, and mixed reality applications as well as computer games. The game simulates a medieval village called SiXton that can be explored and experienced using gestures and speech for in put. SiXton's Curse utilizes multiple independent components for physical simulation, sound and graphics rendering, artificial intelli gence, as well as for multi-modal interaction (MMI). The compo nents are already an integral part of Simulator X's current version. Building on Hewitt's actor model, the Simulator X platform enables the developer to easily exploit the capabilities of modern hardware architectures. A state variable concept is implemented on top of the actor model to grant uniform and easy access to global states and values by using the internal mechanisms of the actor model. Communication via an asynchronous messaging in terface reduces component coupling. The scalability of the actor model provides a uniform concurrency paradigm on different levels of granularity as well as exchangeability of architectural elements and components.