"There are many individuals who are unable to use speech as their primary method of communication. The American Speech-Language-Hearing Association (1991) estimated that there were more than 2 million individuals in the United States who were unable to communicate using speech or had severe communication impairments... These individuals need to use other methods of communication inorder to interact with their environment. The term augmentative and alternative communication (AAC) is used to define these other communication methods. AAC ranges from use of gestures, sign languages, and facial expressions, to the use of alphabet or picture symbol boards, and even sophisticated computer systems with synthesized speech." Glennen, S., & Decoste, D. (1997). Handbook of Augmentative and Alternative Communication. San Diego, CA: Singular Publishing Group, Inc. Click here for more information about this book.