![]() Researchers often distinguish between global coherence, the degree to which each utterance relates to the overall topic under discussion, and local coherence, the degree to which adjoining utterances related meaningfully to one another ( Glosser & Deser, 1992 Kintsch & Vandijk, 1978). Discourse that successfully navigates these challenges is said to be coherent: it consists of a series of well-connected statements all related to a shared topic, making it easy to comprehend ( Foltz, 2007 Glosser & Deser, 1992). 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.Įngaging in discourse is a complex cognitive activity, in which a speaker must identify the topic under discussion, generate a series of statements relevant to this subject and monitor their speech as the discourse unfolds to ensure that they remain on-topic. 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. 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. These results suggest that semantic control deficits give rise to speech that is poorly regulated at the macrolinguistic “message” level. Other aspects of speech production were also impaired but were not significantly correlated with semantic control deficits. 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. Compared with age-matched controls, patients showed severe impairments to global coherence but not to local coherence. 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). To test this hypothesis, we assessed speech coherence in a case-series of stroke patients who exhibited deficits in semantic control. Recent data suggests that executive processes that regulate access to semantic knowledge (i.e., semantic control) are critical for maintaining coherence during speech. ![]() The ability to speak coherently, maintaining focus on the topic at hand, is critical for effective communication and is commonly impaired following brain damage.
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