Figure 1. An expanding virtual room.
Observers wearing a head mounted display occupied a virtual room whose size varied as they walked across it. Moving from the left to the right side of the real room caused the virtual room to expand by a factor of 4. The inset graph shows how the scale of the room changed with lateral distance walked. When the scale was 1, the room was 3 m wide and 3.5 m deep. Because the centre of expansion was a point midway between the eyes, any single image could not reveal the size of the room, as the example views illustrate. Observers reported no perceived change in the size of the virtual room despite correct and consistent information from stereopsis and motion parallax. In the experiment, observers compared the size of two cubes, one seen when the room was small and the other seen when the room was large.