Comprehension of derivational morphemes in words and pseudo-words in semantic variant primary progressive aphasia

• ¹ Université Laval, Canada
• ² Université de Neuchâtel, Switzerland
• ³ Centre de recherche de l'Institut universitaire en santé mentale de Québec, Canada
• ⁴ Centre hospitalier universitaire de Québec, Canada
• ⁵ Université de Montréal, Canada
• ⁶ Centre de recherche de l'Institut universitaire de gériatrie de Montréal, Canada

Introduction According to its classic definition, the morpheme is the smallest meaning unit of language. Accessing the meaning of derivational morphemes helps to understand new or unfamiliar words. The aim of this study was to explore the impact of semantic impairment on the comprehension of derivational morphemes in a group of individuals with semantic variant primary progressive aphasia (svPPA). A few studies report results for derivational morphology in svPPA (Kavé, Heinik, & Biran, 2012; Meteyard & Patterson, 2009) but they did not specifically examine the comprehension of derivational morphemes. Methods Seven French-speaking individuals with svPPA and 14 age, sex and education matched individuals completed a word-to-definition matching task. Targets and foils (2), matched for token frequency, consisted in morphologically complex, semantically transparent words, formed with the base word included in the definition. The task included 6 definition formats and 6 items per format (36 in total). For example, in items with the definition format “De manière [mot de base]” (“In a [base word] way”), targets were formed with the suffix “-ment” which approximately translates to “-ly” in English. Definitions were presented both orally through headphones and visually on a computer screen. Participants had to choose the word that matched the definition by pressing on a button within an eight seconds delay. Because derived words can be processed as a whole and not as a base and an affix, participants were also submitted to a pseudo-word-to-definition matching task in which the correct answer could only be selected by understanding the target morpheme. Each pseudo-word (36) was built in respect to a word item and the foils were formed with the same affixes as their real word counterparts. Results The results of one svPPA participant were excluded from the analysis for the pseudo-word condition because of uncertainty regarding her understanding of the instructions. As shown in Table 1, individuals with svPPA were slower and less accurate in selecting words and pseudo-words that matched a definition. Within group comparisons showed that the control group was faster to choose the correct answer for words than for pseudo-words, while the svPPA group did not show such an advantage. Conclusion The results of the word condition alone cannot rule out the possibility that errors in the svPPA group were caused by difficulty in understanding words rather than in processing derivational morphemes. However, the lexical context provided in this condition did not speed-up the performance of svPPA individuals as it did in the control group. Most importantly, results from the pseudo-word condition showed that in the svPPA group, the association between the morpheme and its meaning was not performed as readily and reliably as in the control group. These results support the involvement of semantic memory in morphological processing.