PubMed · 4481765
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W Frischknecht. 1972. [Alexia as a social problem].. https://pubmed.ncbi.nlm.nih.gov/4481765/
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Letter-by-letter acquired dyslexia (pure alexia) is assumed to be related to the serial encoding of letters, but the evidence for this assumption is somewhat indirect. Here, we demonstrate that the deficit is indeed due to serial encoding by comparing the performance of a letter-by-letter dyslexic reader with the performance of normal readers who were forced to read letter by letter; the data patterns are remarkably similar.
The diagnosis of letter-by-letter (LBL) dyslexia is based on the observation of a substantial and monotonic increase of word naming latencies as the number of letters in the stimulus increases. This pattern of performance is typically interpreted as indicating that word recognition in LBL dyslexia depends on the sequential identification of individual letters. We show, in 7 LBL patients, that the word-length effect can be eliminated if words of different lengths are matched on the sum of the confusability (visual similarity between a letter and the remainder of the alphabet) of their constituent letters. Additional experiments demonstrate that this result is mediated by parallel letter processing and not by any compensatory serial processing strategy. These findings indicate that parallel processing contributes significantly to explicit word recognition in LBL dyslexia and that a letter-processing impairment is fundamental in causing the disorder.
In this single case report we describe our further observations of a patient (ROC) with a classical spelling dyslexia. A word length effect and a script effect were demonstrated. No evidence of semantic processing was obtained with brief tachistoscopic presentations. Single letter identification was unimpaired. In a series of experiments it was shown that her letter-by-letter reading strategy was mediated by explicit letter naming. In particular, it was observed that with successive presentation of the individual letters there was a stepwise function relating her whole word reading to the single letter presentation times. These durations permitted explicit letter naming. When explicit letter naming was prevented by a simultaneous articulatory suppression task, her letter-by-letter reading was significantly impaired. Her performance was compared with a second patient (MRF) who could read but could not spell. His reading was unaffected by articulatory suppression and significantly impaired by a successive presentation of the individual letters of a word. It is argued that explicit letter naming provides an input to the spelling system and thus can be recognized as orally spelled words. We conclude that in the reading-impaired patient there was a lexical deficit compensated for by the operation of a component of her intact spelling system.