Jonah is inching upward in the glass-walled exterior elevator of a 70-story skyscraper. For each story he ascends, he rates his fear on a 100-point scale. At the top, he peers out over a microcosm of office towers, streets and gas stations--that are not really there. While donning a headset that produces three-dimensional images, Jonah is receiving an experimental therapy for a debilitating fear of heights.