• Figure 8: The media player interprets a non-digital device as a pointer.

preview that can be played and paused, detailed title, authors, description, and release date. The text is small but quite readable at this close distance. (d) When Till moves away from the screen to sit on the couch, his currently selected video expands to play in full screen view. Playback is resumed where Till left off; otherwise it starts from the beginning. While Till’s distance from the screen is similar in (a) and (d), the system tells them apart because (a) is associated with a fixed feature of the space (the entrance threshold), while (d) is associated with a semi-fixed feature (the couch).

Non-digital device to surface. Till tires of this video and decides to select a second video from the collection. He pulls out his cell phone and points it toward the surface (see Figure 8). The system recognizes it as a pointer directed at the surface, based upon the phone’s distance from the person and its orientation to the surface. The surface shrinks the running video somewhat to show a row of preview videos at its bottom. A visual pointer on the screen provides feedback of the exact pointing position of Till’s phone relative to the screen. Till then selects the desired videos by flicking the hand downward, and the video starts playing. Alternately, Till could have used another pointing object (such as a non-digital pen) to do the same interaction.

The surface reacts to people’s atten-
tion. Figure 9 shows the various
ways in which the media player
reacts to inattention. (a) Till turns
away from the screen to read a
magazine. After a few moments, the
system interprets this new orienta-
tion as a lack of attention and auto-
matically pauses the video. When
Till turns to look back at the screen,
playback resumes. (b) Till receives
a phone call; he answers. The sys-
tem recognizes the proximity and
orientation of the cell phone to Till
as a call and pauses the video. It
resumes playback after he finishes
the call and puts the phone in his
pocket. (c) If Till and another person
are facing each other for a while,
the system recognizes this as a con-
versation and also pauses.