Speech perception and language comprehension in primary progressive aphasia

Primary progressive aphasia (PPA) is a neurodegenerative disorder characterized by progressive loss of speech and language. Although speech perception and language comprehension deficits are observed in individuals with PPA, these deficits have been understudied relative to production deficits. Recent work has examined receptive language processing at sublexical, lexical, and semantic levels in PPA; however, systematic investigation of these levels of processing within a single PPA cohort is lacking. The current study sought to fill this gap. Individuals with logopenic, nonfluent, and semantic variants of PPA and healthy, age-matched controls completed minimal pairs syllable discrimination, auditory lexical decision, and picture-word verification tasks to assess sublexical, lexical, and semantic processing. Distinct profiles were observed across PPA variants. Individuals with logopenic variant PPA had impaired performance on auditory lexical decision and picture-word verification tasks, with a trend toward impaired performance on the syllable discrimination task. Individuals with nonfluent and semantic variant PPA had impaired performance only on auditory lexical decision and picture-word verification. Evaluation of the types of errors made on the picture-word verification task (phonological and semantic) provided further insight into levels of deficits across the variants. Overall, the results indicate deficits in receptive processing at the lexical-phonological, lexical-semantic, and semantic levels in logopenic variant PPA, with a trend toward impaired sublexical processing. Deficits were observed at the lexical-semantic and semantic levels in semantic variant PPA, and lexical-phonological deficits were observed in nonfluent PPA, likely reflecting changes both in lexical-phonological processing as well as changes in predictive coding during perception. This study provides a more precise characterization of the linguistic profile of each PPA subtype for speech perception and language comprehension. The constellation of deficits observed in each PPA subtype holds promise for differential diagnosis and for informing models of intervention.