Online comprehension of verbal time reference in primary progressive aphasia: Evidence from eyetracking

We conducted an investigation of verbal time reference during sentence comprehension in primary progressive aphasia (PPA) using a visual-world eyetracking approach with auditory sentences. We compared performance of the three main variants of PPA (agrammatic, logopenic, and semantic) against that of age-matched healthy controls during the real-time comprehension of sentences that had past or present time reference indicated by verb inflectional differences. Results revealed impairments in comprehension of past time reference for agrammatic and logopenic PPA participants, with the former showing the most processing difficulty. Conversely, participants with semantic PPA showed a distinct pattern of mild impairment for both past and present time reference, albeit with differing patterns for each. The Past Discourse Linking Hypothesis (PADILIH) provides at least a partial explanation for our findings in the agrammatic and logopenic participants, but not the semantic participants, for whom degraded semantic knowledge may provide a more compelling explanation.