6.2. Materials and Methods 6 97 Movement Control While using the VR equipment the participants were standing still in a spacious room without hazards. The participants were instructed to keep their feet in place, but are free to look around and use their hands to explore the environment. They moved through the virtual hallways using the circular touch pad of the VR handheld game-controllers. By placing their thumb on the touch pad, the participants could control their speed and direction in the virtual environment, allowing for a maximum speed of 2.0 ms−1. Upwards on the trackpad corresponded to the direction that the participant’s head was facing (i.e., the direction perceived as ’forward’ from the participant’s perspective). Through pilot testing in the experimental design stage it was found that aligning the movement control with the head direction was more intuitive compared to leaving the controls statically aligned with the world. In case the participants collided with an obstacle in the virtual environment, they received haptic feedback through a short and strong vibration signal of the VR controller. The participants could also use the VR controllers to explore the edges of the obstacles: in case their virtual hand position in the hallway intersected with an obstacle, the controllers pulsed with a weaker vibration to inform the participant that they were touching the obstacle. Training session All participants performed the experiment in a single one-hour visit, which consisted of a two-part training period, the actual data collection, and a final questionnaire. In the training period, participants were placed in a short corridor featuring two example obstacles. First, the participants practiced moving in the VR environment using the game-controllers. The participants practiced with natural vision (without phosphene vision), until they felt secure in controlling their movement to get past the training obstacles and understood the different vibrations of the collision feedback. Next, a contour filter was applied, reducing the visual fidelity, and more training was performed until the participants securely navigated through the environment. Finally, the participants practiced navigating past the obstacles using the phosphene simulation. An even amount of training was performed with the three different phosphene simulation conditions. The participants could switch back and forth between conditions until they were able to safely navigate the test corridor. Experimental session The experiment was split into three blocks of three trials each. In each block participants would see each variation of object placement and each condition exactly once. The order of the conditions and object layouts inside each block were randomized for each participant. After completing all three blocks, participants had performed all nine possible combinations of the simulation conditions and the variants in obstacle placement. After each block and at the end of the experiment, the participants filled out a survey to collect information on the subjective experience. Experimental task Participants were instructed to avoid collisions as well as they can while still moving as fast as possible. The participants were not informed about the simulation condition before starting each trial. During the experiment, participants kept their feet in place
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