It seems that every few years, 3D technology is in the zeitgeist (with 3d movies). User interfaces are not immune to the frenzy of 3D. However, there is quite a bit of past research in 3D interfaces (I won’t even scratch the surface but see this simple Google Scholar search to start). Much, but not all, relate to navigation in virtual environments, while other research relates to the inclusion of use of depth/perspective. There are still many outstanding issues in the use of 3d in user interfaces; some of which are: use/interaction (input, output), effects on workload, and effects on learning.
In general, 3-dimensional displays (like a perspective view) are perceived to be more natural and possibly require less mental integration than 2-dimensional displays (see this very well-researched U.S./FAA report on multifunction displays; warning PDF). Some of the logic goes like this: when I view a 2d map, I usually turn it into a 3d representation in my head. Showing a 3d representation removes this step (in addition to showing more information). Compare the two types of information displays:
These images come from a user study examining user preferences in map presentation (2d or 3d). The research showed that it depends. The preference data was very complex (see paper) but the preferences were evenly split but those aged 26-40 preferred 3d maps. Males preferred 2d maps while females preferred 3d maps (which seems surprising).
Personally, I switch between 2d and 3d view when I can because each offers information the other does not. I like to examine hikes after the fact (collecting and mapping GPS data). See below; each view gives you different information:
The 2d view gives a good general overview and the intricacies of the trail but shows no elevation information while the 3d view shows terrain but obscures the path (part of it is hidden behind the terrain).
More subtle uses of 3D on websites is the use of the parallax for the illusion of depth. This website showcases some creative uses of this effect. Most websites use it for aesthetic effect, however, I noticed the new Google Nexus One phone uses it in a subtle but useful way to indicate that you are on a different screen (a type of low-level feedback). See the video below. When the user slides to another screen horizontally, the animation of the galaxy changes perspective:
Embedded video (skip to 61 seconds in):
In some cases, when used appropriately, learning can be enhanced by the use of 3d. Researchers Avi Parush and Dafna Berman (in a 2004 paper in the International Journal of Human-Computer Studies) were interested in the use of 3D interfaces for navigation and orientation in a virtual environment. The virtual environment contained the objects that one would normally have on their computer desktop (e.g., files, applications). Will the use of a 3d environment enhance learning and performance? They manipulated whether subjects had two kinds of aids to help: landmarks or a route list. They found that both types of aids help in the learning process but a crucial point was that landmark placement (in either 2d or 3d) was critical.
One commercially available tool that gives users this kind of view of their computer is the BumpTop desktop:
The BumpTop desktop introduces the further complication (on top of 3d) of the nature of interaction. You are using a 2d surface (the touch pad or mouse) to navigate the 3d environment and in some cases using multi-touch gestures (using more than 1 finger). Very cool…but useful? See for yourself:
(post image: http://www.flickr.com/photos/minusbaby/4185007435/)