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?