CSS and Children: Research Results and Future Directions

Background

A processing constraint model has driven the majority of research examining the intelligibility and listener comprehension of CSS with adults. Theoretically, humans have a finite capacity for attention (Moray, 1967), with the brain allocating these resources across tasks. Tasks that require a large amount of processing resources will be completed at the expense of other tasks. Natural speech is characterized by redundant acoustic cues (Klatt, 1987). The information from the natural speech signal is rich, and little attention needs to be allocated by the listener for speech perception. In contrast, synthesized speech contains very few of these redundant cues, requiring increased processing resources for perception (Duffy & Pisoni, 1992). Fewer resources remain for comprehension and other higher order processing, and few remain for any other demands in communication interactions. Children, however, are working within the constraints of a more limited working memory capacity than adults (Case, 1985; Dempster, 1981). The limited capacity will impact the attentional resources available for deciphering synthesized speech. Thus, it may not be possible to generalize the results of research on speech output with adults as listeners.