These are called augmentative communication devices. Speech computers are activated in many different ways. Voice recognition programs respond to verbal instructions or commands. Speech output programs, which have artificial voices, speak for or to the person with a disability. Some computers can create the human voice electronically.
Some computers use human voices in which words or phrases are on audiotape to make sentences.
Touching a symbol on the computer screen triggers the voice taped to interpret that symbol. A person with a speech impairment might use a laptop computer so they can communicate wherever they are. There are many different types of augmentative communication devices. The most common is a board of pictures or symbols. The person points to these pictures to communicate with others.