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Spelling Impairments in Alzheimer's Disease
Overview of Spelling Deficits in Alzheimer's Disease
Alzheimer's disease (AD) is known to cause a general cognitive decline, impacting various domains including memory and language. Spelling impairments are a notable symptom, affecting both written and oral spelling abilities. Research indicates that these deficits are influenced by several factors including orthographic difficulty, word frequency, and the severity of dementia1 2 4.
Lexical and Nonlexical Spelling Deficits
Studies have shown that AD patients exhibit impairments in both lexical (word-based) and nonlexical (sound-based) spelling strategies. This is evident from their poorer performance in spelling real words and pseudowords compared to healthy controls1 7. The decline in spelling accuracy is often attributed to semantic impairments and nonlinguistic functions such as attention and executive control, rather than a disturbance within language-specific processes1 3.
Oral vs. Written Spelling
A significant finding is the difference in impairment between oral and written spelling. AD patients tend to perform worse in oral spelling tasks compared to written ones. This discrepancy is believed to be due to the higher attentional demands of oral spelling4 5. Additionally, AD patients produce more phonologically accurate errors in written spelling, whereas their oral spelling errors are more variable and less accurate4.
Influence of Word Characteristics
The difficulty of spelling in AD patients is also influenced by word characteristics such as length and orthographic regularity. Longer words and those with irregular spelling patterns pose greater challenges. AD patients show a more significant drop in performance with increasing word length compared to healthy individuals6. Moreover, words with arbitrary and rule-based orthography are particularly difficult for AD patients to spell2.
Neural Correlates of Spelling Difficulties
Neuroimaging studies have identified specific brain regions associated with spelling impairments in AD. A left-lateralized cortical network, including areas in the posterior inferior temporal lobe and the superior region of the parietal cortex, has been implicated. Other regions such as the putamen also play a role in these deficits2.
Homophone Spelling and Semantic Influence
AD patients also struggle with homophone spelling, often confusing words that sound the same but have different meanings and spellings (e.g., "doe" vs. "dough"). This issue is linked to a loss of semantic influence on spelling, which becomes more pronounced as the disease progresses9.
Conclusion
Spelling impairments in Alzheimer's disease are multifaceted, involving both lexical and nonlexical processes, and are influenced by word characteristics and attentional demands. These deficits are associated with specific neural correlates and reflect broader cognitive declines in memory and language. Understanding these impairments can aid in developing targeted interventions to support individuals with AD.
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Impaired spelling in Alzheimer's disease: a linguistic deficit?
Alzheimer's disease patients show similar sensitivity to lexical, orthographic, and phonological variables as healthy controls, suggesting that semantic impairment and nonlinguistic functions may contribute to declining writing accuracy in advanced dementia patients.
Non-RCTNeural correlates of spelling difficulties in Alzheimer’s disease
Alzheimer's disease patients exhibit a lexical-semantic spelling deficit, with a mainly left-lateralized cortical network responsible for this impairment.
Observational Study
Very Rigorous JournalImpaired spelling in Alzheimers disease: a linguisticdeficit?
Alzheimer's disease patients show similar spelling accuracy to healthy controls, suggesting semantic impairment and nonlinguistic functions rather than language-specific processes.
Non-RCTComparison between Oral and Written Spelling in Alzheimer's Disease
Alzheimer's disease patients show more impaired oral spelling than written spelling, suggesting increased attentional demands for oral spelling compared to written spelling.
Observational StudySpelling tasks and Alzheimer's disease staging
Oral spelling is the most impaired function in Alzheimer's disease and can differentiate mild and moderate dementia cases, making it a sensitive test for working memory assessment.
Observational StudySpelling and Attention in Early Alzheimer′s Disease: Evidence for Impairment of the Graphemic Buffer
Visual attention impairment, not language impairment, accounts for the phonemically implausible spelling errors in mild Alzheimer's disease patients.
Observational StudyLexical and Nonlexical Spelling Deficits in Dementia of the Alzheimer Type
Dementia of the Alzheimer type is associated with significant impairments in both lexical and nonlexical spelling strategies, with spelling performance correlated to dementia severity but not age of onset or family history of dementia.
Observational StudyComparison of reading and spelling in patients with probable Alzheimer's disease.
Mild reading and spelling difficulties in Alzheimer's patients are due to semantic deficits and nonlinguistic impairments, rather than a specific disturbance in lexical orthographic processing.
Observational StudyDecline in Homophone Spelling Associated with Loss of Semantic Influence on Spelling in Alzheimer′s Disease
Alzheimer's disease patients show an increase in homophone confusions and other spelling errors, primarily due to impaired semantic access to a functional orthographic output lexicon.
Observational StudyQuality of Spelling Breakdown in Alzheimer’s Disease is Independent of Disease Progression
Alzheimer's disease impairs spelling, but the quality of spelling breakdown is independent of disease progression, with a multi-componential disruption of ability.
Observational Study