The relationship between response consistency in picture naming and storage impairment in people with semantic variant primary progressive aphasia

Objective: The progressive loss of stored knowledge about word meanings in semantic variant primary progressive aphasia (svPPA) has been attributed to an amodal "storage" deficit of the semantic system. Performance consistency has been proposed to be a key characteristic of storage deficits but has not been examined in close detail and larger participant cohorts. Method: We assessed whether 10 people with svPPA showed consistency in picture naming across 3 closely consecutive sessions. We examined item-by-item consistency of naming accuracy and specific error types, while controlling for the effects of word-related variables such as word frequency, familiarity, and age of acquisition. Results: Participants were very consistent in their accurate and inaccurate responses over and above any effects of the word-related variables. Analyses of error types that compared consistency of semantic errors, correct responses, and other error types (e.g., phonologically related errors, unrelated errors) revealed lower consistency. Conclusions: Our findings support the assumption that semantic features constituting semantic representations of objects are progressively lost in people with svPPA and are therefore consistently unavailable during naming. Variability in the production of error types occurs when distinctive features of an object are lost, resulting in the selection of semantically or visually similar items or in the failure to select an item and a response omission. The assessment of performance consistency sheds light on the underlying impairment of people with semantic deficits (semantic storage vs. access deficit). This can support the choice of an appropriate treatment technique to maintain or reteach semantic information.