Serious games and immersive virtual reality promote emotional engagement during learning tasks, mostly by providing (1) skill-adapted challenges with performance feedback (for trial and error learning) and (2) enhanced presence (further reactions to multimodal stimuli), respectively. However, it is still unclear how each of these two strategies independently influence emotional states to engage subjects to a task. This study assessed the dimensions of emotion (valencearousal- dominance) of 87 healthy subjects in a virtual game, assigned to 2 groups that were exposed to a different set of 5 trials: Group A experienced game variations by virtual factors affecting user’s presence, whereas group B experienced levels of difficulty, affecting challenge. Emotional reports and 26 features extracted from physiological signals were statistically analyzed. Results showed that presence-based experimental conditions were able to modify the sense of arousal, whereas valence and dominance responded to challenge variation, i.e. were positively correlated with game score. Arousal is likely to increase with low sense of coexistence (social presence) and decrease with low scenario realism (physical presence). Faster breathing and higher skin conductance (SC) were detected at high challenge, whereas heart rate variability and SC increased with higher arousal. The evidence from this study suggests that both strategies can be used to separately influence dimensions of emotion, pointing out the customization of presence-based factors as a promising method to adjust emotional engagement by impacting arousal. Further research should be undertaken to identify the independent effect of single presence factors on emotional states.

Many recent studies in virtual reality (VR) have managed the sense of Presence to assess the suitability of their designs, mainly when focused on learning goals that require high user engagement, such as in serious games for psychomotor training. However, the place and plausibility illusions needed to promote Presence are achieved by combining different VR-based design cues, and their individual contribution to preserving the Presence's engagement/involvement component is still unclear. This article explored the single effect of breaking the sense of Presence per VR factor, i.e., removing VR cues related to Social Presence (human interactions), Self-Presence (embodiment), and Physical Presence (Scenario realism). Thirty-three participants were asked to play an immersive VR simulation of an arcade game three times by experiencing a stepped Break of Illusion in one of the VR factors, i.e., while two factors were kept high, the remaining one was reduced to a low and null (hypothetical) level. The game difficulty was fixed after assessing each person's skills. Results showed that psychophysiology indicators (heart rate and skin conductance) were not affected by the level of illusion, whereas exercise intensity was significantly higher with low body and social presence-based conditions. Moreover, skin conductance was lower in the Social-presence group, which suggests that perspiration is only affected by breaks in realism (scenario and body representations). Based on the obtained evidence, we proposed some guidelines for adapting the design of immersive virtual environments through Breaks in Presence, mainly by changing the realism of the scenario and body representation depending on the skin conductance or the interaction with virtual humans depending on exercise intensity.

The aim of this review is to analyze robotic systems used in lower limb rehabilitation, focusing on signal acquisition, processing, and intelligent system applications. Literature research was done using keywords giving an initial result of 130 publications, to which inclusion and exclusion criteria were applied, giving 58 related publications found during the last ten years. The increasing development of intelligent systems applied to assistive or rehabilitation devices allows one to find new ways of robotic systems usage, in the coming future, in this area. The use of bibliometric analysis software shows the areas of greatest relevance in the conception of this type of system. Finally, from the state-of-the-art research conducted allows to show in this document the most relevant assistive or rehabilitation robotic systems, their main characteristics, their functionality, as well as future trends.

Dynamically Difficulty Adjustment (DDA) has been widely used to preserve engagement in serious and entertaining games, reach better learning, and enhance user performance. A variety of studies suggests that in DDA, task performance (score) rises until hitting a plateau associated with the skill level. However, the sense of engagement is individual and context-dependent, and the effect of DDA on other engagement indicators for immersive virtual environments is still unclear. This study measured objective indicators of engagement while study subjects played an immersive virtual game with DDA to find evidence of dynamic response, similar to game performance. Participants were demanded to perform repetitive upper-limb motions while recording the following indicators: Response Latency as perceptive engagement (elapsed time after sensory stimulus), Exercise Intensity as motion engagement (hand velocity), and psychophysiological responses as emotional engagement (Heart Rate, Skin Conductance, and Respiratory Rate). In addition, 30 features were extracted from the signals to evaluate their variations between time windows. Results indicate that response latency, vertical hand velocity, and heart rate showed significant changes over time during DDA and grew until hitting a plateau, i.e., at the subject's maximum performance. Moreover, some of the features extracted from the signals showed significant differences between time windows, and having strong correlation with the mean of score: max Latency, min velocity on the Y-axis, and mean heart rate, which suggest a promising application for evaluating changes in engagement between different experimental conditions in VR.