HUMAN-COMPUTER INTERACTION
SECOND EDITION
HUMAN-COMPUTER INTERACTION
SECOND EDITION
This allows for the display to include the mouse cursor, which moves with the mouse (pretty obvious really) and also allows for the change in the display when the mouse drags an object.
This model only describes a special subclass of systems, those that are trajectory independent. The mouse position only has a permanent effect at the moment a
Note that the word 'status' is used rather than 'state', as the term will be used to refer to any phenomenon with a persistent value. This includes the position of a mouse on a table and the current screen contents, as well as the internal state of the system. The word 'state' has connotations of the complete state of the system, rather than the selective particular views meant here by status.
The distinction between status and event is between being and doing. Status phenomena always have a value one could consult. For example, you can ask the question 'what was the position of the mouse on the tabletop at 3:27pm?' An event, on the other hand, happens at a particular moment. Here the relevant question is 'at what time did the user press the mouse button?'
Mouse When the user is positioning the mouse pointer over a target, the user's attention will be focused on that target. This is guaranteed in all but a few situations by the feedback requirements of hand--eye coordination. However, this attention may not stay long after the target has been successfully 'hit'.
Text insertion point While typing text, the user will intermittently look at the text just typed and hence the current insertion point. However, because of touch-typing, this is less certain than the mouse except when moving the insertion point over large distances using cursor keys -- another positioning task.
If we know where the user is looking, then we can put information there (not in a status line at the top where no one ever looks). Also, changes at the user's visual focus will be salient and become a perceived event for the user. An example, where the mouse pointer itself is used for information, is the egg-timer or ticking watch icon used when a system is busy.
Finally, recall from Chapter 1 that when people complete some goal, they experience closure. This means that they have a feeling of completeness and go on to the next thing. Closure has implications both on perception and actions. It is why in the mouse positioning task, the user's eye may stray from the target as soon as the target is perceived as 'hit'. In addition, the user may begin some of the actions for the next task, while certain automatic actions terminating the last task are still going on. For example, it is easy to knock a glass from the table by beginning to turn round before fully letting go of the glass.
If we look at Figure 9.5, we see that a number of active agents (Brian, the mailtool and Alison) cause events for one another mediated by status elements (the filestore and screen). This is a very common scenario, especially if you look at fine details of interaction. However, it is also possible to have direct event-based
Screen buttons activated by clicking the mouse over them are a standard widget in any interface toolkit and are found in most modern application interfaces. The application developer has little control over the detailed user interaction as this is fixed by the toolkit. So, the specific results of this example are most relevant to the toolkit designer, but the general techniques are more widely applicable.
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