Dept. of Brain & Cognitive Sci., MIT, 79 Amherst St., Cambridge, MA 02139
The feeling of being present as observer and performer in some environment is hardly ever absent except in cases of pathology. The difficulty in achieving telepresence (or virtual reality) consists in making the observer feel his/her presence in the ``remote'' environment accessed by means of machine interfaces and not in the local and immediate surround. One feels present in a perceived environment when one can anticipate actions that access it. Sensory stimulation evokes these anticipations via an internal model that includes representations of both the observer's body and its parts, objects in the environment, and the consequences of movements of the observer. Utilization of this model by performing actions to verify the anticipated consequences either confirms or disconfirms them. To the extent that the sensory consequences are not anticipated by the model, the sense of presence will suffer. But transmission through this motor-sensory loop informs the model about transforms in space and/or time that may be interposed and in some cases at least adaptation may allow the re-establishment of the feeling of presence.