How can we connect two brains to a video game by means of a BCI, and what will happen when we do so? How will the two users behave, and how will they perceive this novel common experience? In this paper we are concerned with the design and evaluation of multiuser BCI applications. We created a multiuser videogame called "BrainArena" in which two users can play a simple football game by means of two BCIs. They can score goals on the left or right side of the screen by simply imagining left or right hand movements. To add another interesting element, the gamers can play in a collaborative manner (their two mental activities are combined to score in the same goal), or in a competitive manner (the gamers must push the ball in opposite directions). Two experiments were conducted to evaluate the performance and subjective experience of users in the different conditions. In the first experiment we compared single-user situation with one multiuser situation: the collaborative task. Experiment 1 showed that multiuser conditions are significantly preferred in terms of fun and motivation compared to the single-user condition. The performance of some users was even significantly improved in the multiuser condition. A subset of well-performing subjects was involved in the second experiment, where we added the competitive task. Experiment 2 suggested that competitive and collaborative conditions may lead to similar performances and motivations. However the corresponding gaming experiences can be perceived differently among the participants. Taken together our results suggest that multiuser BCI applications can be operational, effective, and more engaging for participants.
We introduce novel interactive techniques to simulate the sensation of walking up and down in immersive virtual worlds based on visual feedback. Our method consists in modifying the motion of the virtual subjective camera while the user is really walking in an immersive virtual environment. The modification of the virtual viewpoint is a function of the variations in the height of the virtual ground. Three effects are proposed: (1) a straightforward modification of the camera's height, (2) a modification of the camera's navigation velocity, (3) a modification of the camera's orientation. They were tested in an immersive virtual reality setup in which the user is really walking. A Desktop configuration where the user is seated and controls input devices was also tested and compared to the real walking configuration. Experimental results show that our visual techniques are very efficient for the simulation of two canonical shapes: bumps and holes located on the ground. Interestingly, a strong "orientation-height illusion" is found, as changes in pitch viewing orientation produce perception of height changes (although camera's height remains strictly the same in this case). Our visual effects could be applied in various virtual reality applications such as urban or architectural project reviews or training, as well as in videogames, in order to provide the sensation of walking on uneven grounds.
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