PubMed · 8337556
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A M Galaburda. 1993. Developmental dyslexia.. https://pubmed.ncbi.nlm.nih.gov/8337556/
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BACKGROUND: Phonological agraphia refers to a condition in which the ability to write nonwords to dictation is impaired, while writing words to dictation is preserved, as is oral repetition of the words and nonwords. This condition has been regarded as reflecting a disconnection within the phonological writing system, and previous neurolinguistic correlations suggested that the anterior-inferior supramarginal gyrus was a crucial link within the system. SETTING: A neurology department of a university hospital. PATIENT: A 51-year-old right-handed man presented with speech disturbances. On initial evaluation of his language, his deficit was consistent with that of conduction aphasia, which improved rapidly to an apparently normal level. A subsequent detailed examination of oral and written repetition of words and nonwords revealed a rather selective form of phonological agraphia. A magnetic resonance imaging scan of his brain showed a focal ischemic lesion at the left posterior superior temporal gyrus and at the underlying white matter. CONCLUSIONS: In contrast to most previously described patients, this patient showed a selective impairment of phonological agraphia in association with a focal infarction restricted to the left posterior superior temporal gyrus, suggesting that this region of the brain is an important node within a wider network of areas that subserve the phonological route for writing.
We report on an Italian brain-damaged patient with impaired written spelling. The patient's errors, in different fonts and scripts, consist mainly of letter substitutions (e.g., filo [thread] --> TILO). The results of various tests indicate that letter substitution errors arise because of a deficit in accessing the letter-form representations supporting written spelling. Letter substitutions occurred predominantly between letters with common strokes (e.g., C and G; b and p). Similarities in terms of global letter shape or letter sound were not valid predictors of letter substitution errors. Letter frequency, consonant-vowel status, and letter gemination were factors affecting letter substitution errors. The results of our investigation suggest that information about letter strokes are stored at the level of letter-form representations, and that access to these representations is sensitive to letter frequency. The results further indicate that letter-form representations do not specify whether a letter is a consonant or a vowel, or is a geminate.
We present the performance of a patient with acquired dysgraphia, DS, who has intact oral spelling (100% correct) but severely impaired written spelling (7% correct). Her errors consisted entirely of well-formed letter substitutions. This striking dissociation is further characterized by consistent preservation of orthographic, as opposed to phonological, length in her written output. This pattern of performance indicates that DS has intact graphemic representations, and that her errors are due to a deficit in letter shape assignment. We further interpret the occurrence of a small percentage of lexical errors in her written responses and a significant effect of letter frequencies and transitional probabilities on the pattern of letter substitutions as the result of a repair mechanism that locally constrains DS' written output.