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ABSTRACT
We report on two types of developmental surface dysgraphia. One type, exhibited by 8 participants, is orthographic lexicon surface dysgraphia, which involves an impairment in the orthographic output lexicon, leading to nonword phonologically-plausible misspellings. The other type, shown by 3 participants, is disconnection surface dysgraphia. In this type, the orthographic output lexicon is disconnected from the semantic system and from the phonological input lexicon, but still contributes to spelling via support to the orthographic output buffer, resulting in mainly lexical phonologically-plausible misspellings (writing be as “bee” but not “bea”).
The specific localization of the impairment in spelling, in the lexicon or in its connections, allowed us to examine the question of one or two orthographic lexicons; four participants who had a deficit in the orthographic output lexicon itself in writing had intact orthographic-input-lexicon in reading. They made surface errors in writing but not in reading the same words, supporting separate input and output orthographic lexicons.
Acknowledgments
We thank Iris Rubin-Zaxenberg and Revital Mor for their important role in participants’ recruitment and testing. We are deeply grateful to the members of the Language and Brain Lab and especially Hadar Green and Maya Yachini for helpful discussions. We also thank Anne Castles, Max Coltheart, Saskia Kohnen, and Lyndsey Nickels, of the beloved yet no longer existing CCD for exciting discussions of these data and models.
Disclosure statement
No potential conflict of interest was reported by the author(s).
Notes
1 The term “potentiophones” is usually used in reading (Friedmann & Lukov, Citation2008). We use it here also for spelling. Examples for potentiophones in spelling in Hebrew include קוטב-כותב, צבת-צוות, שפה-ספה, פרא-פרה.
2 If the orthographic output lexicon impairment is in some way related to frequency (e.g., if the lexicon requires far more exposures than normal in order to encode an entry), then frequency may be involved in determining whether a word will be spelled through the lexicon, and hence whether it will be spelled correctly or not. However, it might be that the lexicon impairment is of a different kind, which has nothing to do with word frequency. In this case, because writing does not pass through the lexicon, no word frequency effect is expected.
3 Irregularity may be considered a special case of polygraphy, where the much-less probable option is selected; or it may be considered a violation of a PGC rule, where the rule takes only the very probable option and does not specify the very improbable rare conversion rule. Take phoneme P, which is converted in a certain orthography in 99.99% of the cases into grapheme G1, and in 0.01% of the cases into G2. The PGC rules may be P->G1 (possibly weighted 99.99) and P->G2 (0.01), in which case an irregular word with P->G2 is a case of polygraphy. Alternatively, the PGC rule may be just P->G1, in which case a word with P->G2 is a case of rule violation, an irregular word.
Silent letters can be seen in a similar way – either as a case of irregularity and rule violation: a rule dictates that a zero phoneme is converted to a zero grapheme. In irregular words like sword and doubt, a zero phoneme is represented with a grapheme, violating the rule. Silent letters may also be cast in terms of biased polygraphy: the rule of conversion of zero phonemes is a conversion to a zero grapheme in most cases, and to w, b, t, l in a tiny fraction of the cases, as in sword, doubt, listen, and talk.
We take here the definition of irregularity as cases of violation of PGC rules. Namely, an extremely biased conversion of a phoneme is a PGC rule, and the very few exceptions are violations of this rule, creating irregularity. These are cases of conversion that no Hebrew writer with normal spelling would use in writing nonwords with the target phonemes.
4 Some words were excluded for some participants due to technical reasons.
5 Could it be that the lexical effects were a mere result of phoneme-to-grapheme conversion probability that happened to be biased toward existing words in the target words we had selected? We think not. Had this been the case, we would expect the PGC probability to affect all participants with surface dysgraphia in the same way. The fact that some of the participants showed a very clear preference for lexical responses for the same words on which others showed no lexical response preference indicates that there is something beyond the PGC probabilities that modulated their spelling. It might indeed be that some of the lexical results of all the participants’ surface errors were due to phoneme-to-grapheme conversion probability, and this rate, for the impaired-lexicon participants may be the base-rate of lexical responses by chance and by conversion probability for all participants. Still, the rate of lexical responses of the participants with disconnection surface dysgraphia was far beyond this base rate.
6 There was no difference between the two runs in EI’s performance, so we preferred to use as much data as we could, and therefore we analyzed both runs.
7 also indicates better writing of potentiophones from semantics than from dictation, for two of the participants. At this point we are not sure what we can conclude from this. Unlike in , the potentiophones in dictation and written naming were different words, so it may be that the ones we used in the dictation task were more susceptible to surface errors, and this is in fact also what we see in the control group. If this is a real difference, then it may be that the connection of the semantic system to the orthographic output lexicon is less impaired for these two participants, or it may indicate that sublexical writing is more readily available in dictation than when writing from semantics.
8 We assume a direct POB-OOB route (in line with models by, e.g., Beeson, Citation1999; Kay et al., Citation1996; Krajenbrink et al., Citation2015; Laiacona et al., Citation2009; Ogden, Citation1996; Whitworth et al., Citation2005). Such route would, for example, allow a child in the first stages of building the orthographic lexicon to spell a word that exists in their POL but not yet in the OOL, by means of accessing the entry in the POL, from there to the phonemes in the POB, and from there, by way of PGC, to a sequence of graphemes in the OOB. Whereas in research we rely on dictation tasks, and hence the sublexical PIB-OOB route, the ecological everyday tasks of writing words not via the orthographic lexicon probably originate in the semantic system and proceed via this POB-OOB route. Notice that this POB-OOB route is not necessary for writing nonwords to dictation, and the direct PIB-OOB seems to be used for this, as demonstrated and discussed in Friedmann et al. (Citation2020).
9 Three of the participants, OR, AN, and HIL are clear instances of a dissociation. NAM did show one lexical effect in writing so she might be a less strong case.
10 We assume that a missing representation and writing via the sublexical route can randomly result in a correct sublexical writing.
11 Concerning individuals with orthographic output lexicon deficits, we assume that different impairments within this lexicon may contribute to the occurrence of surface dysgraphia errors. In some individuals, frequency determines whether or not a lexical entry is stored and accessible. For others, impairment to certain entries is not determined by word frequency.
12 A deficit in the orthographic output buffer itself is ruled out, because, as summarized in , the participants had very few errors of substitution, omission, and addition of non-homophonic letters. A selective deficit of phonologically-plausible misspellings could not arise from the orthographic output buffer.