Maximino Bessa

Abstract
With the consistent adoption of iVR and growing research on the topic, it becomes fundamental to understand how the perception of Realism plays a role in the potential of iVR. This work puts forwards a hypothesis-driven theoretical model of how the perception of each multisensory stimulus (Visual, Audio, Haptic and Scent) is related to the perception of Realism of the whole experience (Subjective Realism) and, in turn, how this Subjective Realism is related to Involvement and Presence. The model was validated using a sample of 216 subjects in a multisensory iVR experience. The results indicated a good model fit and provided evidence on how the perception of Realism of Visual, Audio and Scent individually is linked to Subjective Realism. Furthermore, the results demonstrate strong evidence that Subjective Realism is strongly associated with Involvement and Presence. These results put forwards a validated questionnaire for the perception of Realism of different aspects of the virtual experience and a robust theoretical model on the interconnections of these constructs. We provide empirical evidence that can be used to optimise iVR systems for Presence, Involvement and Subjective Realism, thereby enhancing the effectiveness of iVR experiences and opening new research avenues.

Abstract
Handheld controllers are standard in immersive virtual reality (iVR), but the rise of natural hand-based interactions exposes the limitations of hand gestures, especially for point-and-click tasks with graphical user interfaces (GUI). This shows the need to explore alternative hands-free selection methods. Unlike most studies focusing on the selection task itself, this work evaluates the impact of such methods on multiple dimensions when selections occur alongside another primary task. The tested methods were: head gaze + dwell, leaning, and voice; eye gaze + dwell, leaning, blinking, and voice; and voice-only. Controllers served as the baseline. Methods were further analyzed by pointing and confirming mechanisms. Four dimensions were analyzed: (1) iVR experience, (2) user satisfaction, (3) usability, and (4) efficiency and effectiveness. With 72 participants, results show hands-free methods provide comparable experiences to controllers, suggesting selection methods have a lower impact on the user experience when users focus on a primary task.

Abstract
Throughout the Virtual Reality (VR) literature, we find different terms to define the same concepts as well as the same terms addressing different concepts. This issue can easily cause misinterpretations and difficulty in the analysis of papers from different authors. This work addresses this terminology confusion through a detailed analysis of current key concepts, how they have been employed, comparing them to other concepts, and proposing adaptations to their definitions to reduce conceptual overlap while preserving the original terms. In this work, we reviewed widely used terms in VR: Fidelity, Realism, Immersion, Presence, and Coherence. We also identified and discussed derivative terms, such as Place Illusion, Plausibility Illusion, Sensorimotor Contingencies, Multisensory, Virtual Content, Objective and Subjective Realism, and Objective and Subjective Internal Coherence. We proposed how these distinct concepts can be separated, merged, and linked, providing a clearer terminology for future use and discussing the implications of this terminology.

Abstract
This paper aims to evaluate how different combinations of multisensory stimuli affect the vividness of users' mental imagery in the context of virtual tourism. To this end, a between-subjects experimental study was conducted with 94 participants, who were allocated to either a positive or a negative immersive virtual environment. The positive environment contained only pleasant multisensory stimuli, whereas the negative contained only unpleasant stimuli. For each of the virtual experiences, a multisensory treasure hunt was developed, where each object found corresponded to a planned combination of stimuli (positive or negative, accordingly). The results showed that positive stimuli involving a higher number of sensory modalities resulted in higher reported vividness. In contrast, when the same multisensory modalities were delivered with negative stimuli, vividness levels decreased - an effect we attribute to potential cognitive overload. Nevertheless, some reduced negative combinations (audiovisual with smell and audiovisual with haptics) remained effective, indicating that olfactory and haptic cues play an important role in shaping users' vividness of mental imagery, even in negative contexts.

Abstract