Caroline has cerebral palsy and since birth she has been unable to speak. Her intelligence

and eyesight are both good. She uses a wheelchair constantly; has generally good motor

control in her hands and other parts of her body, except that she gets tired very easily. Her

hands cannot do movements quite as quickly and as finely detailed, as the average person.

It is important that any conversation$-$enabling system be portable and robust: Caroline has

her system on the right arm of her wheelchair, and it consists of a computer, screen,

keyboard, trackball and speakers. Caroline has a stored phrase system, with different

phrases displayed on the screen; she clicks on a phrase to say it out loud, or to change

the category of displayed phrases.

a$)$ The screen interface was carefully designed for Caroline. It does not display the

maximum number of phrases possible, but instead displays significantly fewer phrases,

in a slightly larger size. Why?

b$)$ One possible alternative physical setup for phrase selection is to use a touch screen.

Explain briefly what a touch screen is and suggest why Caroline might prefer her

current set up$.$

c$)$ Why does using a trackball offer Caroline two significant advantages over using a

mouse?

Explain what is wrong with the following interface dialogues of a file manager system, by

also pointing out which of the $8$ golden rules of interface design the dialogue violates:

a$)$ A message of the online help says:

To cancel a file click on the file name and press DEL.

To delete a directory, click on the directory name and press DEL.

b$)$ An error message says:

You have caused a protection fault.

c$)$ An error message says:

The file does not exist. Click on Cancel' or $`$Retry$\text{'}.$

d$)$ An error message says:

You cannot use CTRLD to delete a file.

e$)$ After the user's request to delete a file, this message appears:

Are you sure you want to remove the file? Press $\text{'}$OK$\text{'}.$