Human-Computer Interaction 3e Dix, Finlay, Abowd, Beale

exercises  -  12. cognitive models

EXERCISE 12.3 [extra - not in book]

In a virtual reality design environment, the control device is a small, position- and pressure-sensitive rubber ball. When you pick up and move the ball a new object moves in the virtual environment. When you squeeze the ball the object is fixed in its current position. Consider how you might use the device to move existing items within the environment, and describe this using the 3-state model.

answer available for tutors only

One possibility would be to have a 'hand' or 'claw', which appears in the virtual environment when the ball is picked up and which tracks the position of the (physical) ball. The user moves the claw to an object and squeezes the ball. When the ball is squeezed the virtual claw grabs the object. So long as the ball is kept squeezed the object is moved. When the ball is released the object is dropped into its new position in the virtual environment.

Using the three state model we have:

3-state model

Note however that this solution requires some sort of sensor to tell whether the ball is on the table, such as a light touch sensor, or a sensitive tray.

If there is no such sensor it becomes

In this case there would always be a 'claw' in the virtual space just as there is always a mouse cursor on the screen.

Other exercises in this chapter

ex.12.1 (ans), ex.12.2 (ans), ex.12.3 (tut), ex.12.4 (tut), ex.12.5 (tut)

all exercises for this chapter

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