Incorrect scale perception

Figure 6.9: In the Tuscany demo from Oculus VR, there are not enough familiar objects to precisely resolve depth and size. Have you ever been to a villa like this? Are the floor tiles a familiar size? Is the desk too low?

A virtual world may be filled with objects that are not familiar to us in the real world. In many cases, they might resemble familiar objects, but their precise scale might be difficult to determine. Consider the Tuscany demo world from Oculus VR, shown in Figure 6.9. The virtual villa is designed to be inhabited with humans, but it is difficult to judge the relative sizes and distances of objects because there are not enough familiar objects. Further complicating the problem is that the user's height in VR might not match his height in the virtual world. Is the user too short, or is the world too big? A common and confusing occurrence is that the user might be sitting down in the real world, but standing in the virtual world. An additional complication occurs if the interpupillary distance (recall from Section 4.4) is not matched with the real world. For example, if the user's pupils are $64$mm apart in the real world but only $50$mm apart in the virtual world, then the virtual world will seem much larger, which dramatically affects depth perception. Likewise, if the pupils are very far apart, the user could either feel enormous or the virtual world might seem small. Imagine simulating a Godzilla experience, where the user is $200$ meters tall and the entire city appears to be a model. It is fine to experiment with such scale and depth distortions in VR, but it is important to understand their implications on the user's perception.