The organization of letter-form representations in written spelling: evidence from acquired dysgraphia.

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.