ABSTRACT Developmental Language Disorder (DLD) is characterized by difficulties in the ability to learn and use language and is one of the most common neurodevelopmental disorders (prevalence 7-12%1,2). Though problems emerge in childhood, DLD continues into adulthood3-6 and has profoundly negative effects. Adults with DLD are less likely to seek post-secondary education7-9, may have extended bouts of unemployment9, and have higher rates of depression10. Yet, DLD in adulthood is severely under-researched. An understanding of the language profile is crucial as language abilities in adulthood impact well-being, income, and job performance11. Additionally, there is a clear need to better understand the mechanisms that mediate language abilities in adults with and without DLD. Doing so will help explain theories of DLD12-15 (speed of processing and working memory accounts) and expose a wider range of individual differences in language ability. Examining competition – the activation of competing linguistic representations as speech unfolds – is an ideal approach to exploring these mechanisms. Competition is a fundamental component of language, is well-documented in typical adults16-19, and critically, distinct aspects of competition can be linked to each theoretical account20,21. Our overall objective is to characterize the long-term outcomes of DLD in adulthood (Aim 1) and to identify specific cognitive mechanisms mediating these outcomes (Aim 2). To address our objectives, we utilize a large, pre-existing dataset and participant pool from one of the most comprehensive examinations of DLD to date: the Iowa Longitudinal Study22. We will re-recruit subjects with DLD (n=150) and with typical language (TL; n=250) from this historic cohort, who are now adults (30–34 years old). In Aim 1, we leverage retrospective language measures from kindergarten through 10th grade and collect new outcome measures in adulthood to characterize the long-term outcomes of DLD. We predict that adults with DLD will diverge from adults with TL in language skills that are more complex and higher-level language skills that are important for communication in the workplace11. Further, we predict a fanning effect: some children with DLD will “catch up” to their TL peers in adulthood, some will show evidence of a decline, and others will show stable trajectories. In Aim 2, we measure real-time competition across language modality and level using eye-tracking in the Visual World Paradigm23. According to speed of processing accounts15,20, adults with DLD may be slower than their TL peers to activate competitors and targets. According to working memory accounts21,24, adults with DLD will show sustained competitor activation. Further, we predict that measures related to the dynamics of competition (speed of activation and timing of competitor suppression) will account for variation in language outcomes in adults across the ability spectrum. The proposed work would represent the largest and most comprehensive characterization of language abilities in adults with (and without) DLD to date, inform theories of DLD and general theories of language processing, and provide foundational knowledge toward clinical models of prevention and long-term intervention for adults with DLD.

NARRATIVE Developmental Language Disorder (DLD) in adulthood is severely under-researched, and the consequences are dire: adults with DLD are less likely to seek post-secondary education4 , have extended bouts of unemployment, and higher rates of depression. The current project takes a fundamental step toward illuminating what underlies these profoundly negative effects by characterizing language abilities and mechanisms that explain language deficits in adults with DLD. The proposed research will lay the groundwork for legislative efforts to provide service provision for adults with DLD, and prompt applied research to improve the transition from youth to adulthood in this population.