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By Root 2585 0

levels of control affect the overall task, the direction in which the work is going. Here we determine, supervise, and control the overall structure and goals. Automation can work at any level. Sometimes we really want to maintain control at the lower level. For some of us, it is the nimble execution of the finger or mind that matters. Some of us want to play music with skill. Or we like the feel of tools against wood. Or we enjoy wielding a paintbrush. In cases like these, we would not want automation to interfere. At other times we want to concentrate on higher level things. Perhaps our goal is to listen to music, and we find the radio more effective for us than the piano; perhaps our artistic skill can’t get us as far as can a computer program.

MAKE THINGS VISIBLE: BRIDGE THE GULFS OF EXECUTION AND EVALUATION

This has been a focal theme of POET. Make things visible on the execution side of an action so that people know what is possible and how actions should be done; make things visible on the evaluation side so that people can tell the effects of their actions.

There is more. The system should provide actions that match intentions. It should provide indications of system state that are readily perceivable and interpretable and that match intentions and expectations. And, of course, the system state should be visible (or audible) and readily interpretable. Make the outcomes of an action obvious.

Sometimes the wrong things are visible. A friend of mine, a professor of computer science at my university, proudly showed me his new CD player and its associated remote control. Sleek, functional The remote control unit had a little metal loop protruding from one end. When I asked what it was for, my friend told a story. When he first got the set, he assumed that the loop was an antenna for the remote unit, so he always aimed it at the CD player. It didn’t seem to work well; he had to stand within a few feet of the CD while using the remote. He mumbled to himself that he had bought a poorly designed unit. Weeks later he discovered that the metal hook was just a hook for hanging up the device. He had been aiming the remote at his own body. When he turned the remote around, it worked from far across the room.

Here is a case of natural mappings that fails. The hook provided a natural mapping for function: it indicated which side of the remote control device should be pointed at the CD set. Unfortunately, it provided erroneous information. In making things visible, it is important to make the correct things visible. Otherwise people form explanations for the things they can see, explanations that are likely to be false. And then they find some reason for poor performance—in this example, that the remote was not very powerful. People are very good at forming explanations, at creating mental models. It is the designer’s task to make sure that they form the correct interpretations, the correct mental models: the system image plays the key role.

Remote transmitter units thatneed to be pointed at a receiver should have some visible evidence of the transmitting mechanism. Modern units carefully hide any indication of the signaling method, violating the rules of visibility. My friend searched hard for some clue of the direction to point the device in, and he found one: the hook. And, no, the instruction manual did not say which end of the unit should be pointed at the CD player.

GET THE MAPPINGS RIGHT

Exploit natural mappings. Make sure that the user can determine the relationships:

• Between intentions and possible actions

• Between actions and their effects on the system

• Between actual system state and what is perceivable by sight, sound, or feel

• Between the perceived system state and the needs, intentions, and expectations of the user

Natural mappings are the basis of what has been called “response compatibility” within the fields of human factors and ergonomics. The major requirement of response compatibility is that the spatial relationship between the positioning of controls and the system