Abstract
In this paper, we report a detailed analysis of the impaired performance of a dysgraphic individual, AD, who produced similar rates of letter-level errors in written spelling, oral spelling, and typing. We found that the distribution of various letter error types displayed a distinct pattern in written spelling on the one hand and in oral spelling and typing on the other. In particular, noncontextual letter substitution errors (i.e., errors in which the erroneous letter that replaces the target letter does not occur elsewhere within the word) were virtually absent in oral spelling and typing and mainly found in written spelling. In contrast, letter deletion errors and multiple-letter errors were typically found in oral spelling and very exceptional in written spelling. Only contextual letter substitution errors (i.e., errors in which the erroneous letter that replaces the target letter is identical to a letter occurring earlier or later in the word) were found in similar proportions in the three tasks. We argue that these contrasting patterns of letter error distribution result from damage to two distinct levels of letter representation and processing within the spelling system, namely, the amodal graphemic representation held in the graphemic buffer and the letter form representation computed by subsequent writing-specific processes. Then, we examined the relationship between error and target in the letter substitution errors produced in written and oral spelling and found evidence that distinct types of letter representation are processed at each of the hypothetized levels of damage: symbolic letter representation at the graphemic level and representation of the component graphic strokes at the letter form processing level.
Highlights
What kinds of letter representation are involved in the process of written spelling? That is, what kinds of letter information have to be processed in order to convert the knowledge of how a word has to be spelled into actual lines and curves drawn on a piece of paper? At least two distinct levels of letter representation and processing are assumed within current cogni-tive models of the writing system [19,25,30,41]: first, amodal graphemic representations, subserving both written and oral spelling, and including information about the identity and position of the graphemes within the word; second, abstract representations of letter form, involved in written spelling only, and specifying information required to assign a specific form to graphemes
We show that in a specific type of letter errors found in written spelling only, namely, the noncontextual letter substitution errors, target-error letter pairs were similar in terms of their component strokes, whereas in the contextual letter substitution errors, found in written and oral spelling, target-error letter pairs bore no physical similarity
We looked at the frequency3 of the target and erroneous letter in the noncontextual letter substitution errors produced in written spelling and the letter errors produced in oral spelling
Summary
What kinds of letter representation are involved in the process of written spelling? That is, what kinds of letter information have to be processed in order to convert the knowledge of how a word has to be spelled into actual lines and curves drawn on a piece of paper? At least two distinct levels of letter representation and processing are assumed within current cogni-tive models of the writing system [19,25,30,41]: first, amodal (i.e., modality-independent) graphemic representations, subserving both written and oral spelling, and including information about the identity and position of the graphemes within the word; second, abstract (i.e., effector-independent) representations of letter form, involved in written spelling only, and specifying information required to assign a specific form to graphemes. The assumption that the writing system includes multiple and distinct representations of letter information, is drawn from detailed analyses of the impaired spelling performance of dysgraphic subjects. With reference to a hypothetical functional architecture of the spelling process, such as the one depicted, these analyses first aimed at localizing the deficit of the subjects to one or more components within the architecture. This was achieved by contrasting the subjects’ performance in several spelling tasks (e.g., copy, writing on dictation, oral spelling, etc), each task being supposed to recruit a distinct set of functional components. The characteristics of the subjects’ errors were used to draw inferences about the kind of representations that are processed at the level of the affected component (see [9,45] for arguments in favour of this methodological paradigm that uses data from impaired performance to constrain normal processing theories)
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