There are two types of vocabulary, core and fringe. Core vocabulary is composed of high frequency words that are very versatile. In contrast, fringe vocabulary is composed of words that occur infrequently and lack versatility. Let's compare and contrast core and fringe vocabulary:
|Characteristic||Core Vocabulary||Fringe Vocabulary|
|Number of words||Small number of words||Very large number of words|
|Frequency of use||High frequency||Low frequency|
|Applicability across environments||Applicable to all environments||Applicable to limited environments|
|Applicability across topics||Applicable to all topics||Applicable to limited topics|
|Types of words||Includes a variety of parts of speech||Includes mostly proper names and other nouns|
|Usefulness in a single message||Approximately 80% of the words in a sample of 100 total words will be core, but many of the core words will be used repeatedly, so the number of different words is small.||Approximately 20% of the words in a sample of 100 total words will be fringe. The number of different words will be large, as fringe words are repeated with much lower frequency than core words.|
Now let's look at an everyday phone conversation between friends. The first one says, "What would you like to do?" The second one responds, "I don't know," and the first one replies,"Why don't you come over, and we can watch a movie." There is a total of 22 words in the conversation. Twenty-one of the words are core, and only the word "movie," a noun, is fringe. Core vocabulary is used for 95.4% of the words, and fringe vocabulary is used for 4.5%. "Do," "not," and "you" are used multiple times, so even in this very small sample, the repeated use of core words is evident. There is no repetition of the fringe word. The core words (pronouns: I, you, we; verbs: would, like, do, know, come, can, watch; question words: what, why; other words: a, to, over, not, and) can be used repeatedly for a variety of conversations in many different settings. The fringe word, movie, is useful only when talking about movies.
What is the priority in an AAC vocabulary? A small set of consistent and highly predictable core words that occur frequently, and compose 80% of our messages? Or a very large, unpredictable and inconsistent set of fringe words that compose only 20% of our messages? Core words provide the basic architecture of our messages, and fringe words provide the customized detail. You can say many things using only core vocabulary. If you limit yourself to fringe vocabulary, you most likely will supply one word responses. Try to create a meaningful sentence containing only nouns!
All of us use fringe vocabulary, primarily nouns, that are important to us, such as the names of family members, friends, pets, cities, and states. The names that are important to me are unique to me, and probably only of a few of my fringe words would be important to you. Additionally, you would have difficulty predicting the names that are important to me. My fringe words are my custom vocabulary.
What's the best way to start implementing core vocabulary in AAC? The logical solution is to start with a well-planned and organized core vocabulary, such as the Unity® vocabularies available in PRC's communication devices. Custom, or fringe vocabulary can be added to the device as needed for the individual device user.
The AAC Language Lab provides many lessons and tips for teaching core words. The materials were developed by AAC specialists who have taught Unity to many individuals with great success.