Effect of window size on rate of communication in a lexical prediction AAC system

The study evaluated the effect of three different “window” sizes (the number of words displayed in the word selection menu) on the efficiency of communication in a lexical prediction augmentative and alternative communication (AAC) program. The results showed that a 15-word window produces significantly higher predictions and fewer keystrokes than a 5-word window. The time required to type the messages was statistically equivalent across windows. However, mean keystroke duration was significantly higher in the 15-word window as compared to the 5-word window. This study shows that (1) a saving in keystrokes does not necessarily result in an increase in the rate of communication in lexical prediction programs; (2) searching a word prediction window for target words places significant cognitive/perceptual demands on even individuals with presumably normal cognitive and perceptual abilities (and probably much more so on AAC users); and (3) a 15-word window produces roughly the same rate of communication as the 5-word window but at a significantly greater saving in effort (keystrokes/switch activations).