Sequencing, speech production, and selective effects of aging on phonological and morphological speech errors.

To test age-linked predictions of node structure theory (NST) and other theories, young and older adults performed a task that elicited large numbers of phonological and morphological speech errors. Stimuli were visually presented words containing either /p/ or /b/, and participants changed the /p/ to /b/ or vice versa and produced the resulting word as quickly as possible. For example, the correct response was "bunk" for the stimulus PUNK, and "ripped" for RIBBED. Consistent with NST predictions, the elicited speech errors exhibited selective effects of aging. Some error types decreased with aging. For example, young adults produced more nonsequential substitution errors (as a percentage of total errors) than older adults (e.g., intended bills misproduced as "gills"). However, other error types remained constant or increased with aging. For example, older adults produced more omission errors than young adults, especially omissions involving inflectional endings (e.g. intended ripped misproduced as "np"). In addition, older adults exhibited special difficulties with 2 types of phonological and morphological sequencing processes.