Abstract
Semantic cognition infringes on all aspects of life, and large swathes of the cortex respond to semantic processing. A key component of this is semantic control, which guides retrieval away from pre-potent responses and towards relevant but weak responses (e.g. SALT–ICE, in the context of a road-sign saying “salt spreading”). This is disrupted in Semantic Aphasia (SA) with deficits in “access” rather than storage, and impairments across modalities. This thesis aims to explore the role of semantic control beyond semantics, in experiments involving SA patients and neuroimaging meta-analysis.
We found (1) semantic control deficits had an influence on episodic retrieval when there was a conflict of pre-existing knowledge and task goals. (2) Meta-analysis revealed that semantic control regions responded to divergent thinking. (3) SA patients performance in divergent thinking was creative, but lacked strategic switching, and was negatively impacted by distractors.
This led to three common themes. (1) Firstly, there was a clear influence of the semantic control network beyond semantics. Unconstrained automatic semantic activation and impaired strategy use to guide retrieval negatively impacted episodic and divergent tasks. (2) Semantic control was found to be important for some but not all tasks dependant on task demands. When demand is reduced, SA patients’ show normal levels of creativity and episodic memory. However, challenging retrieval context lead to a reduction in performance, highlighting SA patients reduced semantic control. (3) Finally, we noted parallel performance to pre-existing research in modalities and domains in SA patients.
Overall, these results suggest that the semantic control network has influence on a wide range of processes beyond semantics, and task demands impact performance in SA patients over and above modality and domain.