Implicit-statistical learning in aphasia and its relation to lesion location

Veronika Vadinova,Olga Buivolova,Olga Dragoy,Merel Van Witteloostuijn,Laura S Bos

doi:10.1016/j.neuropsychologia.2020.107591

Abstract

BackgroundImplicit-statistical learning (ISL) research investigates whether domain-general mechanisms are recruited in the linguistic processes that require manipulation of patterned regularities (e.g. syntax). Aphasia is a language disorder caused by focal brain damage in the left fronto-temporal-parietal network. Research shows that people with aphasia (PWA) with frontal lobe lesions manifest convergent deficits in syntax and ISL mechanisms. So far, ISL mechanisms in PWA with temporal or parietal lobe lesions have not been systematically investigated. AimsWe investigated two complementary hypotheses: 1) the anatomical hypothesis, that PWA with frontal lesions display more severely impaired ISL abilities than PWA with posterior lesions and 2) the behavioural hypothesis, that the magnitude of impairment in ISL mechanisms correlates to syntactic deficits in aphasia. MethodsWe tested 13 PWA, 5 with frontal lesions and 8 with posterior lesions, and 11 non-brain-damaged controls on a visual statistical learning (VSL) task. In addition, all PWA completed several linguistic tasks. Reaction times, obtained in the VSL task, were analyzed using linear mixed-effects model. Correlational statistics were used to assess the relationship between VSL task performance and linguistic measures. Results and DiscussionWe did not find support for the anatomical hypothesis as patients with spared frontal regions also manifested impaired ISL mechanisms. This is attributed to a) ISL mechanisms being vulnerable to other cognitive dysfunctions and/or b) ISL mechanisms anatomically extending to the posterior brain regions. Notably, ISL mechanisms were impaired, but not absent in aphasia. With regards to the behavioural hypothesis, we provide empirical evidence of correlation between ISL mechanisms and syntactic, but not lexical impairment in aphasia. We discuss both the theoretical contributions to the debate of domain-independence of ISL mechanisms and clinical implications for implicit language therapy.

Highlights

Detection, encoding and exploitation of regularities in a given environment is essential for the successful learning and use of many skills (Conway and Pisoni, 2008)
While spontaneous and therapy-induced changes in aphasia severity can occur at any time post-stroke (Holland et al, 2016), our study focused on a single point measurement of two functions that were assessed within 3 weeks of each other, which minimizes the negative influence of differences in time post-stroke
Our first key finding regarding the hypothesized anatomical link between Implicit-statistical learning (ISL) mech anisms and lesion location remained unsupported, and we demonstrate that patients whose left inferior frontal gyrus (LIFG) regions were spared, but whose posterior re gions were lesioned, manifest impaired ISL mechanisms

Summary

Introduction

Detection, encoding and exploitation of regularities in a given environment is essential for the successful learning and use of many skills (Conway and Pisoni, 2008). It is believed that domain-general ISL mechanisms are recruited in linguistic processes that require manipulation of patterned regularities, the most prominent example being syntactic processing (Udden et al, 2017). Implicit-statistical learning (ISL) research investigates whether domain-general mechanisms are recruited in the linguistic processes that require manipulation of patterned regularities (e.g. syntax). With regards to the behavioural hypothesis, we provide empirical evidence of correlation between ISL mechanisms and syntactic, but not lexical impairment in aphasia. We discuss both the theoretical contributions to the debate of domain-independence of ISL mecha nisms and clinical implications for implicit language therapy

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