From: Drew Kessler [dkessler@EECS.Lehigh.EDU] Sent: Wednesday, November 17, 1999 10:43 AM To: 3dui List Subject: Re: exo- vs. ego-centric tasks Hi, Doug, Chris's recent reply to your request for thoughts about ego- and exo-centric tasks got me thinking: Where would you draw the line between these types of tasks? For example, would you consider hitting a ball with a tennis racquet an egocentric, or an exocentric task? It seems that this is a line-of-sight task (user's estimation of where to place the racquet so that it contacts the ball is based on the user's 1st person point of view), but also exocentric, as the action happens from a 3rd person point of view (not via ball-cam or racquet-cam). A analogous task would be placing an X on the spot on a map where a missile (on route) will hit. This seems exocentric. It seems to me that surgery, which you put in the exocentric category, is also a similar task. Given these examples, I would come up with the following distinction: - An egocentric task is one where the action of an object is directly based on what can be seen from that object's point of view. - An exocentric task is one where the action of an object is based on what can be seen from another object's point of view. With these definitions, it seems that there are very few egocentric tasks: identification, distance estimation, direction specification (its over there...), skeet shooting (but only if the gun moves with the head, as is often the case), and such. Driving would be a multi-tasked example, where some sub tasks are egocentric (identifying obstacles, deciding which direction to go, deciding if the car should speed up or slow down, etc.) and other are exocentric (turning the wheel to change the cars direction, pressing the gas pedal, actually avoiding obstacles). On the other hand, you could make the distinction between egocentric and exocentric basic on a viewer reference frame: - An egocentric task is one that occurs in the viewer's reference frame. - An exocentric task is one that occurs in some reference frame other than the viewer. What is in the viewer's reference frame is, of course, a matter of perspective (no pun intended). (Are the symbols on the map I am holding part of my reference frame, or the map's reference frame? I would probably think of them as being on the map, but when I write a note beside the symbol, I am likely using my reference frame to decide orientation/size/etc.) I prefer this distinction, but would like to hear other ideas. For one, this distinction makes more sense for a HMD/CAVE vs workbench comparison, as the workbench provides a natural "other" reference frame. On the other hand, classifying tasks appears to be less cut-and-dry. I would put tennis on the egocentric list (I hit the ball at some point relative to me, which is how I figure out where to place my racquet). I would kept surgery on the exocentric list, but mainly because doctors are trained to think in terms of the patient's reference frame (anterior, posterior, etc.). But how about pitching a baseball (or bowling, for you cricket fans...)? The task of directing the ball is in the body's reference frame, but the intended path of the ball is in the field reference frame, and the target of the ball is in the batter's reference frame... These are my thoughts, I would interested in hearing yours... -Drew On Thursday, November 4, 1999, Doug Bowman wrote: > As you may remember from previous postings, I'm thinking about > doing some comparative studies of different VE display types. > One of the differences that seems pretty intuitively clear is > the distinction between an egocentric, 1st person, point of view > (HMDs, CAVE), and an exocentric, 3rd person, point of view > (Workbench). ... > So, two questions: > 1. Are tasks inherently exocentric or egocentric? > 2. If so, what are some examples of each? ... > My current list for #2, which I'm not satisfied with: > exocentric: puzzle assembly, global spatial relationships, surgery,... > egocentric: line of sight tasks, driving, local spatial relationships... -- ___________________________________________________________________________ G. Drew Kessler, Assistant Professor dkessler@eecs.lehigh.edu Electrical Engineering and Computer Science Dept. Office: 118A Packard Lab 19 Memorial Drive West Phone: (610)758-4818 Lehigh University Fax: (610)758-6279 Bethlehem, PA, USA 18015 http://www.eecs.lehigh.edu/~dkessler/