Modeling of user performance with computer access and augmentative communication systems for handicapped people

Abstract

The design of the user interface for an augmentative and alternative communication (AAC) or computer access system is a critical factor in determining a user's p0erformance with a system. A comprehensive, quantitative, and accurate model for alternative access systems is needed to optimize both developers' design decisions and clinicians' system recommendations. This paper presents an application of one possible model, called the GOMS (Goals, Operafors, Mefhods, Selecfion Rules) model (Card, Moran, & Newell, 1983). The model provides a comprehensive description of user behavior based on system-specific parameters as well as the cognitive, perceptual, and motor capabilities of the user. It can be used to predict both task execution and learning times, as well as points of excessive long or short term memory load. The GOMS model is applied here to three interfaces currently used in AAC and computer access systems in order describe and predict user performance, both qualitatively and quantitatively. The three interfaces are: (a) row-column letter scanning; (b) row-column letter scanning combined with word prediction after the first two letter selections only; and (c) row-column letter scanning combined with word prediction after each letter selection. Techniques for applying the GOMS model are discussed, as well as the results predicted by the model. Results for the three systems modeled here suggest the possibility that word prediction interfaces, developed as a faster alternative to row-column letter scanning, may actually be less efficient than letter scanning.