An alternative mouse system. This page provides an image, a description and a list of vendors for alternative mouse systems. As you can imagine, control of the mouse is a must in this graphical user interface world is a must. This can be difficult for users with coordination problems or limited strength or range of movement.
Trackballs are upside down mice, with the ball on top and several buttons.
Look for those which offer the left and right mouse buttons plus one or two more which can be programmed to be a double click or drag lock. These allow the user to use one to 5 switches to control the mouse- the more switches the user can control, the faster the mousing around. Mouse input can also be given by high tech pointing devices, which transmit the location of a transmitter or reflective dot on the user's head to the computer system. Separate switches or just dwelling on a location are used for mouse clicks and drags. These are frequently used with on-screen keyboards for text input by people with limited movement due to quadriplegia or muscular dystrophy.