I STAND teetering on a narrow plank above a deep, yawning pit. I inch forward, stomach lurching, but no matter how hard I try, I can’t step off into the void. Why would I want to? To prove that I am truly rational. Despite appearances, there is actually no pit. I am standing in the Virtual Human Interaction Laboratory (VHIL) at Stanford University in California. This whole 3D scene is nothing more than a precise piece of digital choreography between the sensors that are tracking my every movement, and the two screens - one for each eye - that sit in the bulky head-mounted display that I am wearing. I know all this - yet I can’t jump off. It’s only when I scrape my foot sideways until it meets flat ground where there should be empty space that the illusion is finally shattered.
