140 the design of everyday things could become

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140 The Design of Everyday Things could become standard and easy to apply. It will happen, but it may take considerable time. Alas, like many things that change, new technologies will bring virtues and deficits. The controls are apt to be through touch-sensitive screens, allowing excellent natural mapping to the spatial layouts involved, but lacking the physical affordances of physical switches. They can t be operated with the side of the arm or the elbow while trying to enter a room, hands loaded with packages or cups of coffee. Touch screens are fine if the hands are free. Perhaps cameras that recognize gestures will do the job. ACTIVITY-CENTERED CONTROLS Spatial mapping of switches is not always appropriate. In many cases it is better to have switches that control activities: activitycentered control. Many auditoriums in schools and companies have computer-based controls, with switches labeled with such phrases as video, computer, full lights, and lecture. When � � � � carefully designed, with a good, detailed analysis of the activities to be supported, the mapping of controls to activities works extremely well: video requires a dark auditorium plus control of sound level and controls to start, pause, and stop the presentation. Projected images require a dark screen area with enough light in the auditorium so people can take notes. Lectures require some stage lights so the speaker can be seen. Activity-based controls are excellent in theory, but the practice is difficult to get right. When it is done badly, it creates difficulties. A related but wrong approach is to be device-centered rather than activity-centered. When they are device-centered, different control screens cover lights, sound, computer, and video projection. This requires the lecturer to go to one screen to adjust the light, a different screen to adjust sound levels, and yet a different screen to advance or control the images. It is a horrible cognitive interruption to the flow of the talk to go back and forth among the screens, perhaps to pause the video in order to make a comment or answer a question. Activity-centered controls anticipate this need and put light, sound level, and projection controls all in one location. four: Knowing What to Do: Constraints, Discoverability, and Feedback 141 I once used an activity-centered control, setting it to present my photographs to the audience. All worked well until I was asked a
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question. I paused to answer it, but wanted to raise the room lights so I could see the audience. No, the activity of giving a talk with visually presented images meant that room lights were fixed at a dim setting. When I tried to increase the light intensity, this took me out of giving a talk activity, so I did get the light to where I wanted it, but the projection screen also went up into the ceiling and the projector was turned off. The difficulty with activity-based controllers is handling the exceptional cases, the ones not thought about during design.
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