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.
Highlights
Engaging 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
Maintaining coherence when speaking is a critical skill which may depend on the ability to retrieve and select currently-relevant knowl edge from semantic memory
We investi gated the coherence of connected speech in a case-series of stroke patients with multimodal semantic impairments
Summary
Engaging 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. Older adults are more likely to produce tangential, off-topic utterances in conversation (Arbuckle and Gold, 1993; Glosser and Deser, 1992) and to provide irrelevant information when telling a story (Juncos-Rabadan et al, 2005; Marini et al, 2005) or describing an object (Long et al, 2018) These impairments in coherence hinder effective communication and can be associated with reduced well-being and decreased satisfaction with social interactions (Arbuckle and Gold, 1993; Gold et al, 1988; Pushkar et al, 2000). The target was a picture of either the canonical tool (e. g., hammer), or a non-canonical object that could be used (e.g., brick), presented among a set of five unrelated distractors
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