Optimizing Assisted Communication Devices for Children With Motor Impairments Using a Model of Information Rate and Channel Capacity

For children who depend on devices to communicate, the rate of communication is a primary
determinant of success. For children with motor impairments, the rate of communication may
be limited by inability to contact buttons or cells rapidly or accurately. It is therefore
essential to know how to adjust the device interface in order to maximize each child's rate
of communication. The optimal rate of communication is determined by the Channel Capacity,
which is the maximum value of the Information Rate for all possible keyboard button or cell
layouts for the communication device. We construct a mathematical model for the information
rate based on the relationship between movement time and the number of buttons per screen,
the size of the buttons, and the length of a sequence of buttons that must be pressed to
communicate each word in the vocabulary. We measure the parameters of the model using a
custom-programmed touch-screen interface.