The concept of Virtual Reality (VR) dates back to around 1930, where different technologies and concepts arise. For instance, in 1929 Edward Link created the Link Trainer (further patented in 1931), reported to be the first example of a commercial flight simulator, being entirely electromechanical. Also, in the 1930s, the visionary, science fiction writer Stanley G. Weinbaum brings a story (Pygmalion’s Spectacles) that introduces the early idea of a pair of goggles that makes the wearer experience a fictional world through holograms, smell, taste, and touch. Weinbaum describes uncanny experiences for those wearing the goggles, aligned with the modern experiences of VR. It is in the mid 1950s when cinematographer Morton Heilig developed the Sensorama (further patented in 1962), which resembled a kind of an arcade-style theatre cabinet. The technology integrated in the Sensorama allowed an individual seeing stereoscopic films enhanced with seat motion, vibration, stereo sound, wind, and aromas, which were triggered during the films [1], intending to fully immerse the individual in the film. Since then, many authors have used VR as platforms that support a variety of fields, such as training and learning [2,3,4,5], entertainment [6,7,8], flight and driving simulation [9,10,11], cultural heritage [12,13,14], and scientific and medical visualizations [15,16,17], to cite some. Overall, VR can be referred as a technology that allows for replacing the real world by a synthetic one, making the user believe that she/he is in another realm [18]. It involves a set of technologies that are used to create computer-generated virtual environments where users can experience and interact just as if they would do in real life [19]. To that end, it integrates stereoscopic displays, motion tracking hardware, input devices, and software platforms [20]. The characteristics of VR make it a relevant technology for gaming purposes. The entertainment industry and research is full of examples involving VR applications [6,21]. Gaming in VR is, however, not only restricted to entertainment, but it has been expanded to different fields, mainly with the purpose to learn or train through gaming, usually referred as edutainment or serious games. Some examples can be found in [22,23,24,25]. Simulation techniques are used to build virtual worlds in which users are immersed and to deceive the human senses, so that the perceptual cues that reach the brain are aligned with an alternative reality. These perceptual cues can be of different nature, including acoustic, visual, haptic, smell, and motion stimuli. VR is a consolidated solution in many cases (e.g., driving simulators) as it provides: safety and risk reduction; costs reduction; greater trial availability; no damage; possibility of recreating a variety of situations; and, the possibility of repeating the same situations under the same conditions [18]. VR is a multimodal, interactive technology, since users need to interact with the simulated world as naturally as possible, and do it in a similar way as they would do it the real world. This is quite complex, and therefore in some VR applications interaction is restricted to a certain extent or involving only one or two senses (e.g., visual and sonic stimuli). In fact, due to current technological barriers and/or cost issues, many VR applications are not fully immersive, do not use natural interfaces, and, therefore, do not provide a seamless/credible alternative reality. Therefore, there is a need to provide improved and cost efficient solutions.

The concept of Virtual Reality (VR) dates back to around 1930, where different technologies and concepts arise. For instance, in 1929 Edward Link created the Link Trainer (further patented in 1931), reported to be the first example of a commercial flight simulator, being entirely electromechanical. Also, in the 1930s, the visionary, science fiction writer Stanley G. Weinbaum brings a story (Pygmalion’s Spectacles) that introduces the early idea of a pair of goggles that makes the wearer experience a fictional world through holograms, smell, taste, and touch. Weinbaum describes uncanny experiences for those wearing the goggles, aligned with the modern experiences of VR. It is in the mid 1950s when cinematographer Morton Heilig developed the Sensorama (further patented in 1962), which resembled a kind of an arcade-style theatre cabinet. The technology integrated in the Sensorama allowed an individual seeing stereoscopic films enhanced with seat motion, vibration, stereo sound, wind, and aromas, which were triggered during the films [1], intending to fully immerse the individual in the film. Since then, many authors have used VR as platforms that support a variety of fields, such as training and learning [2,3,4,5], entertainment [6,7,8], flight and driving simulation [9,10,11], cultural heritage [12,13,14], and scientific and medical visualizations [15,16,17], to cite some. Overall, VR can be referred as a technology that allows for replacing the real world by a synthetic one, making the user believe that she/he is in another realm [18]. It involves a set of technologies that are used to create computer-generated virtual environments where users can experience and interact just as if they would do in real life [19]. To that end, it integrates stereoscopic displays, motion tracking hardware, input devices, and software platforms [20]. The characteristics of VR make it a relevant technology for gaming purposes. The entertainment industry and research is full of examples involving VR applications [6,21]. Gaming in VR is, however, not only restricted to entertainment, but it has been expanded to different fields, mainly with the purpose to learn or train through gaming, usually referred as edutainment or serious games. Some examples can be found in [22,23,24,25]. Simulation techniques are used to build virtual worlds in which users are immersed and to deceive the human senses, so that the perceptual cues that reach the brain are aligned with an alternative reality. These perceptual cues can be of different nature, including acoustic, visual, haptic, smell, and motion stimuli. VR is a consolidated solution in many cases (e.g., driving simulators) as it provides: safety and risk reduction; costs reduction; greater trial availability; no damage; possibility of recreating a variety of situations; and, the possibility of repeating the same situations under the same conditions [18]. VR is a multimodal, interactive technology, since users need to interact with the simulated world as naturally as possible, and do it in a similar way as they would do it the real world. This is quite complex, and therefore in some VR applications interaction is restricted to a certain extent or involving only one or two senses (e.g., visual and sonic stimuli). In fact, due to current technological barriers and/or cost issues, many VR applications are not fully immersive, do not use natural interfaces, and, therefore, do not provide a seamless/credible alternative reality. Therefore, there is a need to provide improved and cost efficient solutions.