This paper reviews researches on sentence comprehension deficits and the cognitive orientation switching abilities in two neurological disorders Brocas aphasia and Parkinsons disease (PD). Both patient groups exhibit challenges in sentence comprehension. Individuals with Brocas aphasia show reduced lexical activation and struggle with processing syntactic information when comprehending sentences. While they may retain some comprehension abilities, complex grammatical processing is significantly hindered. In PD, sentence comprehension deficits arise from disruptions in attention, executive control, and action-language networks in the brain which are critical for integrating linguistic information. Regarding cognitive orientation switching, patients with both Brocas aphasia and PD demonstrate impairments, likely due to dysfunction in frontal brain regions that enable flexibility in thinking. Broca's patients struggle with changing response strategies, while PD patients have difficulty learning new classification rules and are challenged by distractions. There is evidence that reduced cognitive switching abilities can interfere with effective syntactic processing during sentence comprehension. The review highlights neurological underpinnings and manifestations of comprehension and cognitive flexibility deficits in these two disorders. Further research can provide greater insight into the nuanced interactions between language and domain-general cognition.
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