Going off the rails: Impaired coherence in the speech of patients with semantic control deficits

Abstract

The ability to speak coherently, maintaining focus on the topic at hand, is critical for effective communication and is commonly impaired following brain damage. Recent data suggests that executive processes that regulate access to semantic knowledge (i.e., semantic control) are critical for maintaining coherence during speech. To test this hypothesis, we assessed speech coherence in a case-series of stroke patients who exhibited deficits in semantic control. Patients were asked to speak about a series of topics and their responses were analysed using computational linguistic methods to derive measures of their global coherence (the degree to which they spoke about the topic given) and local coherence (the degree to which they maintained a topic from one utterance to the next). Compared with age-matched controls, patients showed severe impairments to global coherence but not to local coherence. Global coherence was strongly correlated with the patients’ performance on tests of semantic control, with greater semantic control deficits associated with poorer ability to maintain global coherence. Other aspects of speech production were also impaired but were not significantly correlated with semantic control deficits. These results suggest that semantic control deficits give rise to speech that is poorly regulated at the macrolinguistic “message” level. The preservation of local coherence in the patients suggests that automatic activation of semantic associations is relatively intact, such that each utterance they produce is connected meaningfully to the next. However, in the absence of control processes to constrain semantic activation, the content of their speech becomes increasingly distant from the original topic of discourse. This study is the first to investigate the impact of semantic control impairments on speech production at the discourse level and suggests that patients with these impairments are likely to have difficulties maintaining coherence in conversation.

Similar neural networks respond to coherence during comprehension and production of discourse

“…Executive control is necessary to ensure that coherence is maintained during speech production, such that discourse remains focused on the topic at hand and avoids irrelevant statements (Arbuckle & Gold, 1993;Marini & Andreetta, 2016). Supporting this view, performance on cognitive control tasks predicts the coherence of speech in older adults (Gold, Andres, Arbuckle, & Schwartzman, 1988;Kintz et al, 2016;Wright, Koutsoftas, Capilouto, & Fergadiotis, 2014) and deficits in coherence and narrative organization are commonly found in the speech of patients with impaired executive functions (Ash et al, 2006;Coelho, 2002;Hoffman, Cogdell-Brooke, & Thompson, 2020;Marini, Zettin, & Galetto, 2014). Recent evidence has identified a role for a specific aspect of executive function, namely semantic control, in the maintenance of coherence (Hoffman, Loginova, & Russell, 2018a).…”

The cognitive and neural underpinnings of discourse coherence in post-stroke aphasia

“… 9 , 14 ) or personal discourse (e.g. 4 , 7 , 16 , 17 ). Different discourse tasks can lead to variations in connected speech and discourse features in aphasia, including production quantity, 18–21 lexical and semantic features, 22 and coherence.…”

Anterior Connectivity Critical for Recovery of Connected Speech after Stroke

“…fractional anisotropy) predicted a measure commonly used to examine discourse, that is, the cohesiveness of one sentence to another measured by the use of personal pronouns to refer to previously named agents. However, coherence reflects not only syntax, but also lexical, semantic and executive control abilities 28,29 making it difficult to interpret which aspect of connected speech critically depended on the ILF. These results highlight the potential importance of the AF and ILF for the recovery of broad aspects of connected speech, but the small subject sample size and lack of lexical-syntactic connected speech measures in participants during the acute stage of stroke leave open the question of which white matter tracts are critical for the recovery of connected speech.…”