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Reading lexically without semantics: evidence from patients with probable Alzheimer's disease
1Department of Neurology, University of Maryland Medical School, Baltimore, USA.
Summary
Patients with severe semantic impairment can still read aloud words accurately, even those with irregular spellings. This suggests oral reading relies on nonsemantic lexical processes, not just meaning.
Area of Science:
- Neuroscience
- Psycholinguistics
- Cognitive Psychology
Background:
- The lexical model of oral reading posits that word pronunciation involves both sublexical and lexical processes.
- Severe semantic impairment may impact oral reading, particularly for words with exceptional spellings, according to existing models.
Purpose of the Study:
- To investigate the role of semantic knowledge in oral reading for individuals with severe semantic impairment.
- To test predictions of the lexical model of oral reading concerning the impact of semantic impairment on reading exception words.
Main Methods:
- Administered a battery of lexical-semantic and oral reading tasks to neurologically normal controls and individuals with probable Alzheimer's disease (AD).
- Assessed oral reading accuracy for regular and exception words in AD patients with varying degrees of semantic impairment.
Main Results:
- Individuals with moderate semantic impairment read all words accurately.
- Severely impaired AD patients showed no difference in reading regular versus exception words, and reading accuracy was not correlated with semantic knowledge of exception words.
- Reading performance in severely impaired patients did not align with predictions based solely on semantic processing.
Conclusions:
- Findings support a lexical model of word reading that incorporates nonsemantic pathways.
- Orthographic representations can directly activate phonological representations, bypassing semantic mediation.
- Oral reading, especially for exception words, may rely on direct lexical access rather than semantic processing.