Disturbed visual processing contributes to impaired reading in Alzheimer's disease

Area of Science:

• Neuroscience
• Cognitive Psychology
• Ophthalmology

Background:

• Alzheimer's disease (AD) is characterized by cognitive decline, including potential impacts on language and visual processing.
• Oral reading impairment is a common symptom, but its underlying mechanisms in AD are not fully understood.
• The role of specific visual processing deficits in oral reading difficulties in AD requires further investigation.

Purpose of the Study:

• To investigate the relationship between visual processing dysfunction and oral reading impairment in patients with probable or possible Alzheimer's disease (AD).
• To determine if specific visual processing deficits, particularly those involving the left ventral temporal-occipital regions, are associated with oral reading impairments in AD.
• To differentiate the contribution of visual processing deficits from lexical semantic impairments to oral reading difficulties in AD.

Main Methods:

• The study included 17 patients diagnosed with probable or possible Alzheimer's disease (AD).
• Participants underwent assessments of oral reading abilities and various visual processing tasks, including word discrimination in different fonts and object photograph orientation.
• Dementia severity was controlled for in the analysis to isolate the relationship between specific cognitive functions and reading performance.

Main Results:

• A significant relationship was found between single-word oral reading impairments and difficulties discriminating words in different fonts and object orientations, even when controlling for dementia severity.
• These visual processing functions are believed to rely on the integrity of left ventral temporal-occipital visual association regions.
• No significant relationship was observed between reading performance and spatial localization tests (parietal lobe function) or unfamiliar face discrimination (right inferotemporal lobe function).
• Crucially, no relationship was found between reading ability and lexical semantic impairment, suggesting visual deficits are more directly implicated than semantic ones.

Conclusions:

• Visual processing deficits, particularly those related to high-level visual processing in the left temporal-occipital lobes, significantly contribute to impaired oral reading in Alzheimer's disease (AD).
• These findings suggest that neuropathological changes in these specific visual processing areas are a key factor underlying reading difficulties in AD.
• The results highlight the importance of considering visual processing deficits when assessing and understanding oral reading impairments in the context of Alzheimer's disease.