The effect of omitted cues on alphabet -supplemented intelligibility
The practice of using alphabet supplementation to increase speech intelligibility for people with dysarthric speech has been documented for that past 25 years. Alphabet supplementation involves pointing to the first letter of each word as it is spoken. Alphabet supplementation can increase sentence-level intelligibility by an average of 26%. Traditional alphabet supplementation research assumes complete and accurate alphabet cues for all spoken words. No documentation exists about the effect of omitted alphabet cues on speech intelligibility.
This study investigated the effect of omitting alphabet cues from alphabet-supplemented speech by systematically omitting the cues for words within different word classes. Specifically, no alphabet cues were omitted in a 100% alphabet supplementation condition, cues for all nouns were omitted in an alphabet-minus-noun condition, cues for functor words were omitted in an alphabet-minus-functors condition, and cues for verbs were omitted in an alphabet-minus verbs condition. The study used sentence stimuli from two different speakers. Each experiment compared sentence intelligibility scores between habitual speech (natural dysarthric speech with no intervention) and the four alphabet-supplemented conditions, and between the 100% supplementation condition and the three omitted conditions.
Results showed statistically significant differences between the habitual speech condition and all but one of the alphabet supplementation conditions. No statistically significant differences occurred between the 100% alphabet supplementation condition and any of the manipulated conditions.