A Rate Index for Augmentative and Alternative Communication

Abstract

Individuals with severe speech disability can benefit from the use of augmentative and alternative communication (AAC) speech output assistive technology. The recent development of tools and methods for measuring AAC performance through the collection and analysis of language samples has advanced the clinical practice of this field. The definition of a new summary measure for characterizing performance of AAC systems in use is presented. The summary measure, here named rate index, is the average communication rate (in words per minute) divided by the selection rate (in bits per second) for the language sample. Thus the unit of measure for the rate index is words per bit. The rate index provides for the comparison of communication rates adjusted for differences in selection rates. Rate index comparisons can be made between individuals using similar or different systems or for one individual under different conditions. The clinical value of the rate index is the identification of opportunity for improved communication performance. Demonstrated rate index data also can serve as evidence to be used in the selection of AAC systems. The language sample data reported in this paper were collected using automated language activity monitoring (LAM).