The Role of Word Properties in Performance on Fluency Tasks in People with Primary Progressive Aphasia.

People with primary progressive aphasia (PPA) present language difficulties that require lengthy assessments and follow-ups. Despite individual differences, people with PPA are often classified into three variants that present some distinctive language difficulties. We analyzed the data of 6 fluency tasks (i.e., "F", "A", "S", "Fruits", "Animals", "Vegetables"). We used random forests to pinpoint relevant word properties and error types in the classification of the three PPA variants, conditional inference trees to indicate how relevant variables may interact with one another and ANOVAs to cross-validate the results. Results indicate that total word count helps distinguish healthy individuals (N = 10) from people with PPA (N = 29). Furthermore, mean familiarity differentiates people with svPPA (N = 8) from people with lvPPA (N = 10) and nfvPPA (N = 11). No other word property or error type was relevant in the classification. These results relate to previous literature, as familiarity effects have been reported in people with svPPA in naming and spontaneous speech. Also, they strengthen the relevance of using familiarity to identify a specific group of people with PPA. This paper enhances our understanding of what determines word retrieval in people with PPA, complementing and extending data from naming studies.