HUMAN-COMPUTER INTERACTION
SECOND EDITION
HUMAN-COMPUTER INTERACTION
SECOND EDITION
The design and building of meeting rooms is both expensive and time consuming, but less sophisticated facilities are more widely available. The simplest is the hardcopy whiteboard, which has some of the advantages of an electronic whiteboard (and with greater resolution). If these were more closely coupled to a computer system, they would have even more scope. Transparent LCD screens for putting on top of an overhead projector can give any computer a vast screen image. In the simplest case this can just be manipulated by one person, but if several computers are networked together and use commercial shared screen software (see below in Section 13.5.1), one can obtain a similar effect to that of the more expensive conferencing facilities. However, experience of the various meeting room projects has shown that the social dynamics are very fragile and the difference between a successful meeting environment and a complete disaster is narrow.
The idea of a shared screen forming an electronic whiteboard is not confined to face-to-face meetings. One can easily imagine using the same software which runs in a meeting room, working between several sites. That is, we can take the synchronous co-located meeting room software and use it for synchronous remote meetings. As before, each participant's screen shows the same image, and the participants can write on the screen with the same sort of floor control policies as discussed earlier. There are additional problems. First, the participants will also require at least an audio link to one another and quite likely video as well. Remember that the social protocols used during lenient floor control, not to mention the discussion one has during a meeting, are difficult or impossible without additional channels of communication. As well as the person-to-person communications, the computer networks may have trouble handling the information. If there are delays between one person writing something on the board and another seeing it, the second participant may write to the same location. A situation which is easily avoided in the co-located meeting could become a major problem when remote. Many researchers in the area blithely assume that such problems will be solved by cheaper high-bandwidth telecommunications, such as ISDN.
In order to make the whiteboard effect more realistic, several systems are arranged so that participants write by hand directly onto large screens. The writing is either filmed by camera (using complex arrangements of mirrors), or captured digitally using a sensitive screen. The image of one participant's writing is then displayed on the others' screens. The effect is very like all being able to write at once on the same screen, except that the other participants' writing will be slightly less
One system, VideoWhiteboard [235], arranges its lighting and cameras such that you can see not only the other participants' writing, but also shadowy images of their hands and bodies, getting gradually dimmer and more out of focus as they move away from the screen. For two participants, it is rather as if your colleague is writing on the other side of a smoked glass panel. When used by more than two participants, your ghostly colleagues can appear to occupy the same space and move through one another! This sounds rather disconcerting, but the users soon get used to the effect and are able to interpret one another's body language, even as a soft-focus shadow.
A third variation of the shared work surface is where the participants write on a sheet of paper on their desktop, which is then filmed from above. The images from each participant are then mixed and displayed on a screen in each participant's work area. By looking at the screen while they point and write, the participants can refer to one another's work. The advantage of such a system is that the participants' individual paper work is easily integrated into their shared environment. The desktop images can also be mixed with a shared computer screen, so that paper and computer work can be mixed. One such system, the TeamWorkStation [121], has been used for the remote teaching of Japanese calligraphy. The student is able to paint letters on paper or on the computer screen and see these strokes overlaid with the teacher's strokes. In this system, the participants also have a face-to-face video link.
Most of the groupware tools we have discussed require special collaboration-aware applications to be written. However, shared PCs and shared window systems allow ordinary applications to be the focus of cooperative work. Of course, you can cooperate simply by sitting together at the same computer, passing the keyboard and mouse between you and your colleague. The idea of a shared PC is that you have two (or more) computers which function as if they were one. What is typed on one appears on all the rest. This sounds at first just like a meeting room without the large shared screen. The difference is that the meeting rooms have special shared
A shared window system is similar except, rather than the whole screen, it is individual windows which are shared. While the user works with unshared windows, the system behaves as normal, but when the user selects a shared window the shared windowing system intervenes. As with the shared PC all the user's keystrokes and mouse movements within the window are broadcast to the other computers sharing the window.
Shared editors may be text based or include graphics. For simplicity, we shall just consider text. Even so, there are a wide range of design options. Should you have a single insertion point with some form of floor control to avoid interleaving, or should you have one insertion point per participant? Assuming you have several insertion points, do you just see your own, or do you see your colleagues' insertion points as well, and if you can see them should they be identified by the user's name or be anonymous? In addition to the insertion point options, there is the issue about what you should see. Do all the participants see the same part of the screen, so if one participant scrolls, so do all the rest? Or do we allow different views on the document so that one participant can edit the beginning of the document while another edits the end?
Thinking about the shared view vs. different view options, it at first seems obvious that we should allow people to edit different parts of a document. This is certainly true while they are working effectively independently. However, as soon as they begin to discuss the text together -- that is, really collaborate synchronously -- problems arise: 'I don't really like that line at the top' you say; 'I just wrote that, I think it's really good' your colleague replies. Possibly the end of your good working relationship, and, sadly, unnecessary. Your screens show different parts of the document and so the line at the top of your screen (which you disliked) is not the one your colleague has just written (Figure 13.7). Of course, the participants know
These problems are precisely why the principle of WYSIWIS ('what you see is what I see') is used in meeting rooms. Even minor differences between displays, such as lags between the appearance of one participant's typing on the others' screens, can cause severe problems -- no wonder different views cause trouble. Of course, WYSIWIS is not always appropriate, for example if we want to edit different parts of a document. Neither is it a solution to all problems. For example, if two people try to scroll the shared view at the same time, we have scroll wars. People find this conflict harder to resolve than typing clashes. This is probably because scrolling is a less direct and less predictable action anyway, and thus it is more difficult to diagnose what is going wrong. This suggests that better locking of scrollbars and visual clues are required. As we will discuss later (Section 13.7) graphics toolkits do not make such modifications easy.
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