Dual keyboard Lightwriters permit continuous two-way communication with the communication partner. They are designed to allow people without speech or hearing to communicate directly with people who do not use sign language, and have also been found very suitable to some people with autism.
The user types on one keyboard and their message appears on both displays. The person they are communicating with reads the message on the second display and responds on the second keyboard; each message appears simultaneously on each display, and is also spoken if a speech synthesiser is fitted.