In press in Cortex

Letter Position Dysgraphia

Aviah Gvion1,2,3 and Naama Friedmann3

1Ono Academic College, Kiryat Ono, Israel 2Reuth Medical Center, Tel Aviv, Israel

3Tel Aviv University, Tel Aviv, Israel�

The article describes AE, a Hebrew-speaking individual with acquired dysgraphia, who makes mainly letter position errors in writing. His dysgraphia resulted from impairment in the graphemic buffer, but unlike previously studied patients, most of his errors related to the position of letters rather than to letter identity: 80% of his errors were letter position errors in writing, and only 7% of his errors were letter omissions, substitutions, and additions. Letter position errors were the main error type across tasks (writing to dictation and written naming), across output modalities (writing and typing), and across stimuli (migratable words [words in which letter migration forms another word], irregular words, and nonwords). Letter position errors occurred mainly in the middle letters of a word. AE’s writing showed a significant length effect, and no lexicality, migratability, or frequency effects. His letter position deficit was manifested selectively in writing; he made no letter position errors in reading, demonstrating the dissociability of letter position encoding in reading and writing. These data support the existence of a letter order function in the graphemic buffer that is separate from the function responsible for activating letter identities.

1. Introduction

This study reports on a Hebrew-speaking individual with acquired dysgraphia, who makes

mainly letter position errors in writing. His deficit is located in the graphemic buffer, and its

selective nature sheds light on the functions of this buffer and their internal organization. The

graphemic buffer is a stage in the process of writing that follows the orthographic output

lexicon and precedes the allographic stage. To write a word, the writer accesses the

orthographic output lexicon, in which orthographic representations are stored and activated.

The selected graphemes are held for a short time in the graphemic buffer and are then

transmitted in the correct order to the allographic stage, where the abstract letter forms are

stored. The graphemic buffer also temporarily holds the products of the phoneme-to-

grapheme conversion in the course of nonword writing.

A selective impairment in the graphemic buffer results in graphemic buffer dysgraphia.

This dysgraphia has been investigated thoroughly in several case studies of acquired

dysgraphia and in several languages (Annoni et al., 1998; Blanken et al., 1999; Buchwald and

� We thank Maya Yachini for her helpful comments and discussions of this research and manuscript. This research was supported by the Israel Science Foundation (grant No. 1296/06, Friedmann).

Letter position dysgraphia 2

Rapp, 2003, 2004; Caramazza et al., 1987; Caramazza and Miceli, 1990; Cotelli et al., 2003;

Cubelli, 1991; Kobubo et al., 2001; Miceli et al., 1997; Posteraro et al., 1988; Rapp and

Kong, 2002; Sage and Ellis, 2004; Schiller et al., 2001; Tainturier and Rapp, 2004; see Miceli

and Capasso, 2006 for a review).

The types of error that result from a deficit in the graphemic buffer are letter identity

errors - substitutions, additions, and omissions, and errors of letter position within the word,

both in real words and in nonwords. A graphemic buffer impairment does not yield errors that

characterize central dysgraphias, such as regularizations, homographic and semantic

substitutions, morphological errors, or lexicalizations, nor does it show effects of

imageability, grammatical category, or abstractness (Caramazza et al., 1987). The writing of

individuals with graphemic buffer dysgraphia is affected by word length because the buffer is

a temporary store with limited capacity (Caramazza et al., 1987; but see Sage and Ellis, 2004

for a different view). The graphemic buffer is assumed to be shared by the different spelling

output modalities, such as writing, typing, and oral spelling (Caramazza et al., 1987); thus, a

deficit in the graphemic buffer causes errors in all orthographic output modalities. This

contrasts with selective impairments in later stages of writing (the allographic store, the

graphemic motor patterns for writing, the letter name conversion mechanism, articulatory

programming for oral spelling, and specific motor programming for typing), which affect

only the relevant output modality.

Caramazza et al. (1987) and Caramazza and Miceli (1990) suggested that the

orthographic representations temporarily stored in the buffer are multidimensional structures

and that, in addition to letter identity, these representations include dimensions that specify

gemination, orthographic-syllabic structure, and the grapheme’s consonant-vowel status.

Case studies of selective impairments support this view. Cotelli et al. (2003), for example,

reported an individual with dysgraphia who made errors predominantly in vowel identity

(85% of the errors). He mainly made vowel letter substitutions (always replacing vowels with

other vowels); he inserted few vowel letters, and he did not transpose any letters. Buchwald

and Rapp (2003) reported two individuals with acquired dysgraphia, both of whom retained

the orthographic consonant-vowel structure of most written items. The patterns of errors

found in these case studies support the notion that the graphemic buffer has distinct functions

that can be selectively impaired.

Crucially for our study, McCloskey, Badecker, Goodman-Schulman, & Aliminosa (1994)

proposed that the multidimensional graphemic representations encode letter position and

letter identity in two separate tiers. This approach was also taken by Brenda Rapp and her

Letter position dysgraphia 3

colleagues (Buchwald and Rapp, 2004; Rapp and Kong, 2002), who suggested that the

graphemic buffer is responsible for at least two functions: activation and selection. Namely,

the graphemic buffer is involved in the activation of the graphemes constituting the word, and

it is responsible for the serial selection of the individual graphemes from the set of active

letters. According to these accounts, which assume distinct encoding for letter identity and

letter position, two distinct types of graphemic buffer deficit are expected following a

selective deficit in each of the two functions: a selective deficit in the activation component

and a selective deficit in the serial selection of individual letters. Indeed, Buchwald and Rapp

(2004) reported two individuals with such an activation deficit (RSB and BWN) and an

individual with a selective deficit in serial selection (JRE). The writing of these patients

differed with respect to their sensitivity to lexical frequency: whereas RSB’s and BWN’s

spelling accuracy showed an effect of lexical frequency, JRE’s did not. Buchwald and Rapp

accounted for this difference by assuming that the activation component of the graphemic

buffer is sensitive to the strength of lexical encoding, but the selection component is not. The

dissociable pattern of performance between the function of letter identity activation and the

function of serial selection was also demonstrated in a letter probe task, in which the patients

were asked to judge whether a particular letter appeared in a word that was presented

auditorily. RSB, who had a letter identity deficit, failed on this task, but JRE, who had a

deficit in serial selection, performed well (Rapp and Kong, 2002).

Importantly, the distinction between the two functions of the graphemic buffer predicts

not only differences in frequency effect and letter detection task between the selective

impairments in activation and serial selection, but also different error patterns. A selective

deficit in the letter identity function (which Rapp termed the “activation” component) is

expected to result in letter substitutions, additions, and omissions, whereas a selective deficit

in the letter position function (“serial selection”) should result in letter position errors, with

the correct letters in wrong positions.

And indeed, some studies of graphemic buffer dysgraphia have reported individuals who

predominantly omitted or substituted letters and who either did not transpose letters or did so

rarely (Cotelli et al., 2003; Kay and Hanley, 1994; Kokubo et al., 2001; Posteraro et al., 1988;

Shallice et al., 2000; see Miceli and Capasso, 2006 for a review). However, letter position

errors almost always occurred alongside letter identity errors (Annoni et al., 1998; Badecker

et al., 1990; Buchwald and Rapp, 2003; Caramazza et al., 1987; Caramazza and Miceli, 1990;

Cubelli, 1991; Jónsdóttir et al., 1996; McCloskey et al., 1994; Miceli et al., 1997, 2004; Sage

and Ellis, 2004; Tainturier and Caramazza, 1996; Tainturier and Rapp, 2004). One individual

Letter position dysgraphia 4

who made predominantly letter position errors was reported by Blanken et al. (1999). They

reported on the writing of LM, a multilingual patient, who made writing and spelling errors in

the three languages that she mastered (German, English, and Finnish). Her errors consisted

mainly of transposing middle adjacent letters; she made other types of errors much less

frequently (2%). However, her general error rate was relatively low (in writing to dictation,

she made 2%–6.7% errors in the various tasks in English, 3.5%–7.9% errors in German, and

6% errors in Finnish).

Another individual who made a high rate of letter position errors, though not selectively,

was LB, reported by Caramazza and Miceli (1990). Only 28% of his errors were letter

position errors, but many of his letter substitution, omission, and addition errors involved

letters that existed in the words, errors that may also indicate a letter position deficit

(Friedmann and Rahamim, 2007). However, LB also made a considerable number of letter

identity errors (33%) that cannot be accounted for by a letter position deficit.

This article presents a case study of a Hebrew-speaking individual who shows a high rate

of letter position errors and only a few letter identity errors, providing evidence for a

distinction between the graphemic buffer mechanisms encoding letter identity and those

encoding letter position.

A selective letter position impairment has also been identified in reading, in Hebrew and

Arabic speakers with acquired dyslexia (letter position dyslexia; Friedmann and Gvion, 2001;

Friedmann and Haddad-Hanna, in press) and in speakers of Hebrew and Arabic with

developmental dyslexia (Friedmann, Dotan, and Rahamim, in press; Friedmann and Gvion,

2005; Friedmann and Haddad-Hanna, in press; Friedmann, 2007). The main error type that

individuals with letter position dyslexia make is letter position errors within words, mainly of

middle letters. Because the deficit in reading is located before the orthographic input

lexicon,1 and the information about letters arrives in the lexicon without information about

the position of middle letters, lexical effects such as frequency and migratability affect

reading in individuals with letter position dyslexia. Migratable words, namely, words like

beard, tired, and cloud in which letter migration creates another existing word (bread, tried,

could), yield more errors than nonmigratable words like computer and dyslexia, in which no

1 In studies of individuals with letter position dyslexia (Friedmann and Gvion, 2001; Friedmann and Rahamim, 2007), letter position errors occurred not only in reading aloud, but also in reading comprehension, as measured by lexical decision, same-different decision, and definition tasks, pointing to a deficit in the early stage of orthographic-visual analysis, which is responsible for encoding of letter position within words (Ellis, 1993; Ellis et al., 1987) or a letter’s position relative to exterior letters (Humphreys et al., 1990; Peressotti and Grainger, 1995). No parallel phonological output deficits were evinced, further supporting a deficit in the early stage of reading, rather than in phonological output stages.

Letter position dysgraphia 5

lexical item results from letter migration (Friedmann and Gvion, 2001; Friedmann and

Rahamim, 2007). Crucially, however, if the letter position deficit in writing is in the

graphemic buffer, no such lexical effects are expected, because the graphemic buffer follows

the orthographic lexicon. In this study we examine whether the position-encoding functions

in reading and writing are separate, by testing whether our participant made letter position

errors in reading as well as in writing. We further test whether lexical effects such as

frequency and migratability, which characterize letter position impairment in reading, are

also present in letter position impairment in spelling.

In this article, we explore the types of errors our participant makes in writing and their

characteristics (section 3), investigate the effects on his writing (length, lexicality, frequency,

and migratability, section 4), test whether he has a letter-position-encoding deficit in reading

as well (section 5), and compare his reading and writing (section 6).

2. Participant

AE, a right-handed 61-year-old man, was referred to the clinic following a right temporo-

parietal lesion as a result of cerebral hemorrhage (see appendix A for his MRI scan). AE had

13 years of education; prior to the stroke he worked as a journalist, and he had no premorbid

reading or writing disorders. AE’s reading and writing were tested 3 years and 2 months after

his stroke. At that time, besides the reading and writing impairments, which are the focus of

this study, AE had limited phonological working memory and agrammatism.

At the same time that AE’s writing was assessed, his phonological short-term memory

was tested using the FriGvi working memory battery (Friedmann and Gvion, 2002). The

working memory assessment showed limited digit, word, and nonword spans in all the recall

tasks: digit span was 5 (normal average = 6.94, SD = 1.07); phonologically dissimilar

2-syllable word span was 3.5 (normal average = 5.33, SD = 0.72); phonologically similar

2-syllable word span was 2.5 (normal average = 4.29, SD = 0.63). AE showed no significant

word length effect on memory: he had a span of 3 for 4-syllable words (normal average =

4.32, SD = 0.63) and a span of 3.5 for 2-syllable words. He also had a very limited span of 2

for 2-syllable nonwords (normal average = 3.32, SD = 0.48). AE had a lexicality effect of 1.5

items, calculated by the difference between his basic word span (the 2-syllable

phonologically dissimilar word list) and his nonword span. This effect did not differ from the

normal effect (normal average = 2.03, SD = 0.61; 1.64, SD = 1.21 for his age group), further

establishing a limited phonological short-term memory deficit and rejecting the possibility of

Letter position dysgraphia 6

a semantic working memory deficit (see Martin and He, 2004; Martin et al., 1994). AE also

performed below normal levels in recognition spans, in which he was requested to point to

the n words that appeared in the list, which were presented with additional n+1 distractor

words, rather than orally recall the words. In a word recognition span test, his span was 4.5

(normal average = 5.78, SD = 0.36); in the Hebrew version of the listening span test, adapted

for individuals with aphasia (as it involved no reading, and pointing instead of spoken

production), his span was 4 (normal average = 5.79, SD = 0.43) (see Friedmann and Gvion,

2003a, and Gvion and Friedmann, 2007, 2008 for a detailed description of the test battery).

On the basis of language assessment using the Hebrew version of the WAB (Kertesz,

1982; Hebrew version by Soroker, 1997) and BAFLA (a test battery for agrammatic

comprehension and production; Friedmann, 1998), AE was diagnosed with nonfluent

agrammatic aphasia. He displayed characteristic agrammatic speech: his speech was

nonfluent, and he produced short, ungrammatical utterances, used mainly simple sentences,

and had impaired production of complex sentences and Wh-questions. His sentence

comprehension was also characteristic of agrammatism: he showed poor comprehension of

reversible object relatives and topicalized sentences, and relatively good comprehension of

simple active subject-verb-object sentences and subject relatives.

Importantly, apart from his phonological working memory limitation and agrammatism,

AE’s conceptual and lexical abilities were normal. He had intact conceptual abilities, as

assessed using the SHMITA picture association task (Biran and Friedmann, 2007); intact

lexical-semantic knowledge, as assessed using the synonym judgment task, PALPA 49 (Kay

et al., 1992; Hebrew version by Gil and Edelstein, 1999); and intact lexical retrieval, as

assessed using the SHEMESH naming test (Biran and Friedmann, 2004).

3. An Assessment of AE’s Writing

To assess AE’s spelling ability and to identify the functional location of his writing deficit,

we examined his writing in various tasks and modalities: writing to dictation, typing to

dictation, written naming, and copying. We also examined the way he wrote various types of

words and nonwords. In this section, we present the writing tasks, the analysis of AE’s errors

- the results of all the writing tests are summarized in Table 1. We also present analyses of

effects on his errors – length, lexicality, migratability of words, and frequency – and the

position of errors.

Letter position dysgraphia 7

3.1. Writing to dictation

3.1.1. Writing single words

The first assessment of AE’s writing included a test of writing to dictation, which consisted

of 808 words (created from the TILTAN screening test, made up of 147 words, administered

twice in two different sessions; and the TILTAN migratable words test, made up of 514

migratable words; Friedmann and Gvion, 2003b). The word list was constructed in such a

way as to detect various types of dysgraphia. To detect graphemic buffer dysgraphia, it

included words of varying length, from 2 to 11 letters (M = 4.83, SD = 1.15), and migratable

words: 354 words had a lexical potential for migration of middle letters (284 of them of

adjacent middle letters), 116 words had a lexical potential for migration of exterior (i.e., first

and last) letters, and 226 words had a lexical potential for both exterior- and middle-letter

migrations. All words had a lexical potential for neglect errors on the left side (namely,

substitution or omission of letters of the leftmost letter in these words would create another

existing word), and 456 of the words had a lexical potential for right neglect errors.

The word list was also geared to detect surface dysgraphia: most of the words (763 of the

808) could not be written correctly solely on the basis of phoneme-to-grapheme conversion;

lexical information was needed in order to write them correctly, because of the inclusion of

phonemes that could be mapped to one of several graphemes, or because of irregular spelling;

137 of these words were potentiophones, i.e., words that, when written via phoneme-to-

grapheme conversion, might result in another existing word (like now for know; Friedmann

and Lukov, 2008).

The list also contained words from various lexical categories and words of differing

morphological complexity: 182 of the words were (exclusively) verbs, 244 were nouns (108

abstract and 136 concrete and highly imageable), 46 were function words, and 264 were

morphologically complex words (beyond the usual morphological structure of Semitic words,

which are constructed from a root and a template). This list of 808 words was dictated to AE

for writing in nine sessions.

Results

AE wrote 530 of the 808 words (65.6%) correctly. The majority of his errors (77%) were

letter position errors, and only 7.9% of the errors were letter identity errors. The distribution

of his errors is detailed in Table 1.

Letter position dysgraphia 8

Table 1 - Distribution of error types in the various spelling tasks Correct/total % position

errors Pure position errors

Migrations Doubling Position+

morph/om/ sub/add

Morph Om Sub Add Mix

Writing single words to dictation

530/808 77% 162 15 38 41 15 4 3

Typing 118/185 90% 46 6 8 5 2

Written picture-naming

71/100 83% 16 3 5 3 1 1

Total word writing 719/1093 80% 224 24 51 49 18 5 0 3

TOTAL WORDS (66%) (14%) (13%) (7%)

Writing nonwords 15/60 73% 11 1 21 3 8 2 3

Morph = morphological error; Om = letter omission; Sub = letter substitution; Add = letter addition; Mix = more than one identity error in the same word. Six of the position+ errors were position errors in incomplete words that AE gave up writing.

We classified his letter position errors into pure letter position errors, which are errors that

only involved writing a letter in an incorrect position, and position plus errors, in which AE

made a letter position error and another error in the same word. AE made 177 pure letter

position errors. These errors included 51 adjacent migrations, that is, errors in which one

letter moves across one adjacent letter, causing two adjacent letters to exchange positions

(marble > mabrle, sometimes termed “exchange errors”; this count includes migrations in 4-

letter words, in which middle-letter migration can only give rise to an adjacent migration),

and 111 nonadjacent migrations, that is, errors in which a letter moves across more than one

letter (dear > dare, sometimes termed “movement errors”). Under pure letter position errors

we also included 15 errors that involved writing a letter in an incorrect position, in addition to

writing it in the correct position. We termed these errors doubling errors. In these cases, the

doubled letter migrated either to a position between other letters (example > examplpe), or to

replace another letter (example > exampme).2

2 Evidence that doublings are indeed letter position errors rather than letter identity errors comes from comparing additions of letters that exist in the target word (doubling) with additions of letters that do not (rain > rairn / railn), and comparing substitutions with letters that exist in the target word with substitutions with letters that do not exist in the target word (rain > rarn / raln). Among AE’s errors, there were 7 additions of letters that existed in the target word, and no addition of other letters; 12 substitutions with letters that existed in the target and only 5 substitutions with another letter, indicating that these errors were clear instances of migrations of a letter that existed in the word to another position in the word, rather than incidental letter additions and substitutions. Namely, the impaired serial selection selected the letter both in the correct position and in another, incorrect position. Such doubling errors are typical in letter position dyslexia, and might result from the fact that since the two instances of a doubled letter differ only in their position within the word, when an individual’s letter position encoding is impaired, the individual cannot tell these letters apart and therefore cannot tell when reading or writing whether the word contains one or two instances of the same letter (see the discussion of doubling errors in Friedmann and Rahamim, 2007 and in Friedmann, Kerbel, and Shvimer, in press). We should also note that letters that appear twice in a word in Hebrew are not geminates, each letter has its own phonological representation, and even when the double letters are adjacent, an unwritten vowel often separates them (Yachini & Friedmann, 2008).

Letter position dysgraphia 9

In addition to the pure letter position errors, AE made 38 “position plus” errors, which

involved both a letter position error and omission, substitution, or addition of a letter; 3 of

these “position plus” errors were responses in which he made a position error and then gave

up writing the rest of the word when he recognized the error.

Of AE’s errors, 41 could be interpreted as morphological errors (similar to his errors in

reading aloud and in spontaneous speech, though fewer in number), including omissions or

substitutions of one or two letters that were morphological affixes).

Thus, the pattern evinced in the writing task consisted predominantly of letter position

errors. Importantly, AE made only a few pure letter identity errors: in writing the 808 target

words, he made only 22 such errors (see the rightmost columns omission, substitution,

addition, and mixed errors on Table 1). These findings – frequent letter position errors and

few letter identity errors – point to a deficit in the letter position rather than the activation

component of the graphemic buffer, indicating that AE’s impairment lay in selecting the

letters in the appropriate order from a set of correctly activated letters.

AE made no errors that characterize central dysgraphias. He made no semantic errors,

indicating no deep dysgraphia. Moreover, despite the extremely irregular nature of Hebrew,

such that most of the words could potentially expose a surface dysgraphia, he made no errors

that characterize phoneme-to-grapheme writing: he made no regularization and no

homophonic letter selection errors, indicating that he had no surface dysgraphia.

3.1.2. Writing nonwords

To further test the hypothesis that AE’s writing deficit resulted from a graphemic buffer

deficit rather than a lexical deficit, we tested his writing of nonwords. If only words are

impaired, then the deficit stems from an impaired lexicon. However, if nonwords are also

impaired, the deficit can be localized in the buffer, which is shared by the lexical and

sublexical spelling routes. We dictated to AE a list of 60 nonwords with an average length of

5 letters (range 3–7 letters) (TILTAN screening; Friedmann and Gvion, 2003b). The list

consisted of 20 migratable nonwords, created by changing the order of adjacent middle letters

in existing words (משחבים; ‘computers’ transposed into ‘copmuters’), and 40 nonwords

created by replacing a single letter in existing words.

Results

AE wrote correctly only 15 of the 60 nonwords (25%). In this test, too, he made letter

position errors (see Table 1 for error distribution), which occurred in 73% of the errors. He

Letter position dysgraphia 10

showed similar rates of middle-letter position errors in nonwords of different lengths and in

words of corresponding lengths: he made 25%, 48%, and 36% errors in nonwords of 4, 5, and

6 letters, respectively, and 13%, 48%, 36% errors in words of the same lengths. His error rate

in migratable and nonmigratable nonwords was similar, χ2 = 1.6, p = .21.

AE made 33 letter position errors: 12 were pure letter position errors (6 adjacent, 5

nonadjacent, including 1 adjacent and “giving up” response, and 1 doubling), and 21 were

“position plus” errors. Letter identity errors occurred on 16 words. All of AE’s letter position

errors involved middle letters. Of the total 45 errors, only 11 resulted in lexicalization. Thus,

AE’s word and nonword writing showed a similar error rate and similar error types with

respect to letter position, but his nonword writing showed a higher rate of letter identity errors

(substitutions, omissions, and additions) than his word writing.

Crucially, AE’s letter identity errors did not result from impaired phoneme-to-grapheme

conversion, as indicated by his flawless (22 out of 22) performance in writing a grapheme to

a single dictated phoneme. The identity errors in writing dictated nonwords might have

resulted from his limited phonological input working memory (see detailed information on

his phonological spans in the Participant section). This conclusion is supported by AE’s

performance in nonword repetition. When we asked him to repeat 26 of the dictated

nonwords, he showed similar difficulty, and was able to repeat only 18 of them (69%)

correctly; he made 94% letter identity errors in repetition, most of which led to

lexicalizations.

The impaired writing of nonwords and the fact that nonword writing included position

errors as did the word writing, supports the ascription of AE’s impairment to a deficit in the

graphemic output buffer, rather than at a prior, lexical, level. The higher rate of errors in

writing non-words compared to words was also reported in other cases of graphemic buffer

dysgraphia (Miceli, Benvegnù, Capasso, and Caramazza, 1995; Shallice et al., 2000).

3.2. Typing

To test whether AE’s letter position errors indeed resulted from a graphemic buffer deficit or

whether they stemmed from a deficit in a later component of writing, we further tested

spelling using the typing modality. We dictated to AE 185 of the single words also dictated to

him for writing. This time he was asked to type them on a computer keyboard. Because we

used the same words for writing and typing, we dictated them in two sessions: in the first

Letter position dysgraphia 11

session, AE wrote half of the words and typed the other half, and in the second session, two

weeks later, he wrote the second half and typed the first half.

Results

AE typed 118 of the 185 words (64%) correctly (see Table 1). In this task, too, most of his

errors (90%) were letter position errors. His 52 pure letter position errors included 30

adjacent, 16 nonadjacent, and 6 doubling migrations. The error rate was similar in typing and

writing, χ2 = 0.22, p = .64, and the pattern of errors was similar: mainly letter position errors,

and only a few (3%) letter identity errors, indicating that the letter position deficit in spelling

is independent of the modality of writing. This supports the hypothesis of a deficit that is

located no later than the graphemic buffer.

3.3. Written picture-naming

According to the criteria suggested by Caramazza et al. (1987) for deficits that characterize

graphemic buffer dysgraphia, the errors should occur similarly not only across output

modalities, but also across writing tasks and input types. We therefore further tested AE’s

writing with written picture-naming.

AE was asked to write the names of items shown in 100 color pictures from the

SHEMESH picture-naming test (Biran and Friedmann, 2004). The test includes target words

of varying length (2–7 letters), gender, frequency, regularity, and semantic category. Of the

target words, 10 had a lexical potential for middle-letter migration, 44 had a lexical potential

for exterior-letter migration, and 74 were sensitive to surface dysgraphia (mainly because of

homophonous consonant letters). Each picture was introduced individually without time

limitation.

Results

AE wrote 71% of the words correctly. Of his errors, 83% were letter position errors. His pure

letter position errors included 11 adjacent migrations (including a migration in a 2-letter word

that naturally could not give rise to a nonadjacent migration), 5 nonadjacent migrations, and 3

doublings. He also made 5 “position plus” errors. The distribution of his errors is detailed in

Table 1. When asked to name the items in the same pictures aloud, AE named all of them

correctly.

Thus, the results of the Experiments reported in sections 3.1-3.3: writing to dictation,

typing to dictation, and written picture naming, summarized in Table 1, all show a very clear

predominance of letter position errors.: 80% of AE’s errors in spelling included a letter

Letter position dysgraphia 12

position error, whereas only 7% of his errors were letter identity errors, suggesting an

impairment in the letter position function.

3.4. Immediate copying

If indeed AE’s deficit lies in the graphemic buffer, no specific deficits are expected in letter

formation or in immediate word copying; these tasks do not involve the graphemic buffer,

particularly because words can be copied one letter at a time. To examine this prediction, we

visually presented to AE, for immediate copying, 40 words with a lexical potential for letter

position errors: 35 words with a lexical potential for middle-letter migration, and 5 words

with a lexical potential for exterior-letter migration. The words were 4–7 letters long. Each

word was presented individually, without time limitation, and stayed in front of AE until he

finished copying it.

Results

AE copied all the words rapidly and effortlessly, stating that he felt it was an easy task. He

copied 36 words (90%) correctly on first trial, and made no error of letter form. He

immediately corrected the four errors (all of them were pure letter position errors) without

hesitation.

3.5. Interim summary – the spelling results indicate a deficit in the graphemic buffer

Thus, the results of the writing tasks 3.1-3.4 indicate that AE’s dysgraphia resulted from a

deficit in the graphemic buffer. He made only errors that are characteristic of graphemic

buffer dysgraphia: mainly letter position errors, few letter identity errors, and made no

semantic errors and no regularization errors. His deficit did not occur in a stage later than the

graphemic buffer, as indicated by his good copying and by the fact that he made the same

type of errors in writing and typing. His errors did not stem from a lexical deficit, either, as

indicated by his similar rate of letter position errors in writing nonwords and words.

A dysgraphia that results from a deficit in the graphemic buffer is further characterized by

a length effect, by more errors in middle positions, and by a lack of lexical effects such as

lexicality of response and frequency. The analyses in the next section test these aspects of

AE’s writing.

Letter position dysgraphia 13

4. Further analyses of AE’s error pattern in writing

4.1. Is there a length effect on writing?

Because the graphemic buffer is a limited memory store, a word’s length affects it

considerably; thus, length effect serves as an important marker for locating an individual’s

deficit in the graphemic buffer rather than in an earlier lexical stage (Badecker et al., 1990;

Baxter and Warrington, 1983; Blanken et al., 1999; Buchwald and Rapp, 2003, 2004;

Caramazza et al., 1987; Cotelli et al., 2003; Cubelli, 1991; Posteraro et al., 1988; see Miceli

and Capasso, 2006 for a review). Therefore, we performed an analysis of length effect on

AE’s writing of single words in the word dictation list, on his written naming, and on the

words he typed. To avoid a spurious word length effect that actually emerges from

morphology rather than from length, we excluded from this analysis the morphologically

complex words on which he made morphological errors.3

A total of 1,060 words of 2–11 letters were analyzed (24 two-letter words, 81 three-letter

words, 380 four-letter words, 334 five-letter words, 193 six-letter words, 37 seven-letter

words, 7 eight-letter words, 1 nine-letter word, and 3 eleven-letter words). We counted the

total number of errors of all types as well as letter position errors and letter identity errors as a

function of the number of letters in the target word.

Results

AE’s writing showed a very clear length effect: longer target words yielded more errors,

Rpb = .96, p < .0001.4 A length effect was also evinced when calculated separately for letter

position errors, Rpb = 0.97, p < .0001 (see Fig. 1), and for letter identity errors, Rpb = .87, p =

.01 (letter identity errors occurred only in longer words: no identity errors in 2- and 3-letter

words, 1% in 4-letter words, 3% in 5-letter words, 6% in 6-letter words, and 25% in words of

7 or more letters). Longer words were more vulnerable to both letter identity and letter

position errors. This effect of the target word’s length on AE’s writing further establishes the

conclusion that the graphemic buffer is the source of AE’s writing deficit.

3 Note that excluding these words went against the hypothesis that we would find a length effect, because the words we excluded from the analysis were 33 long words that included errors. Even without them, however, the length effect was very robust. 4 Sage and Ellis (2004) reported that the effect of length on their patient BH’s spelling was considerably reduced once orthographic neighborhood, imageability, frequency, and age of acquisition were controlled for. AE’s spelling was not affected by the lexicality of the target or by its frequency; hence, the length effect could not be attributed to lexical effects in his writing.

Letter position dysgraphia 14

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

2 3 4 5 6 7 8-11

Fig. 1 - The effect of number of letters in the target word on letter position error rate in AE’s writing.

4.2. Middle- versus exterior-letter migration: Is there an exterior-letter advantage?

In letter position dyslexia, a bow-shaped effect is evident in migration errors: letter position

errors in reading occur mainly in middle letters, whereas the first and last letters are much

less susceptible to position errors (Friedmann and Gvion, 2001; Friedmann and Rahamim,

2007). A similar pattern has been reported in writing for some individuals with graphemic

buffer disorder (Buchwald and Rapp, 2004; Caramazza et al., 1987; Caramazza and Miceli,

1990; Jónsdóttir et al., 1996; Posteraro et al., 1988; Tainturier and Caramazza, 1996). To find

out whether AE’s writing also shows such a bow-shaped effect, we analyzed his letter

position errors in writing with respect to the position of the letters that migrated to other

positions in the word.

This analysis showed that most of the letter position errors in AE’s writing involved

middle letters; exterior letters were much less susceptible to such errors. Of the 299 letter

position errors that AE made in writing, 92% occurred in middle letters (of these, 73%

involved adjacent letters and 27% nonadjacent ones5) and only 8% in first and last letters.

This higher susceptibility of the middle letters to letter position errors did not result from

the greater number of middle letters compared with exterior letters: In 4 letter-words, in

which the number of middle and exterior letters is identical, 3 times more errors occurred in

middle than in exterior letters. In 5 letter-words, where there are only 1.5 times more middle

letters than exterior letters, almost 10 times more errors occurred in middle letters, and in 6-

letter words, where there are twice as many middle letters than exterior letters, there were 12

times more letter position errors in middle letters. 5 For the adjacent/nonadjacent analysis, we included only words of 5 or more letters, because nonadjacent letter position errors are possible only in words with more than 2 middle letters.

Letter position dysgraphia 15

The word’s length affected only letter position errors in middle letters: these occurred in

10, 28, 36, 40, and 91 percent of the 4, 5, 6, 7, and 8-11 letter words respectively. The few

letter position errors that occurred in exterior positions were unaffected by word length

(6, 5, 3, 3, 3, 6, and 0 percent errors respectively). All 26 letter identity errors occurred in

middle position.

4.3. Is there a lexicality constraint on AE’s writing errors?

If indeed the letter position errors in AE’s writing result from a deficit in the serial selection

of graphemes, following activation of the letters’ identity, and if these errors arise later than

the lexical stages, errors should not necessarily create lexical items. In Hebrew, the

probability that a letter position error will accidentally create another existing word is very

high, because of the very dense orthographic neighborhood and the language’s Semitic

morphology (for discussion, see Friedmann and Gvion, 2001; Friedmann and Rahamim,

2007; Frost, 1992). To be able to analyze quantitatively whether AE had a tendency to

produce lexical responses, we undertook two analyses. First, we compared AE’s error rate on

migratable words, i.e., words in which a middle letter migration creates another existing

word, with his error rate on nonmigratable words of the same length. Had there been a

lexicality constraint on AE’s writing, we would have expected migratable words to be more

susceptible to errors than nonmigratable words. We also counted, for words of 5 letters in

which some possible letter position errors create an existing word and other letter position

errors create nonwords, how many of the possible letter position errors create an existing

word (e.g., the word smile has 1 possible lexical middle letter position error and 4 possible

nonlexical ones). We then compared this expected rate of lexical responses with the number

of AE’s letter position errors that created an existing word, divided by the total number of

letter position errors he made on these words. If AE’s writing is affected by lexicality, we

would expect that the lexical migrations would be selected and that the rate of lexical

responses would exceed the rate expected by chance. However, if AE’s deficit is postlexical,

migratable and nonmigratable words should yield similar error rates, and the percentage of

lexical responses when both lexical and nonlexical errors are possible should not differ from

the chance probability of accidentally producing a lexical item. Since almost all position

errors occurred in middle letters (see Section 4.2), we calculated potentials for middle-letter

migrations.

The first comparison, between migration error rates in 4-letter migratable and

nonmigratable words (233 migratable words, 146 nonmigratable words), yielded no

Letter position dysgraphia 16

difference in error rates in the two types of target words, χ2 = 0.02, p = .88 (11% and 12%

middle-letter position errors, respectively). The same analysis for 5-letter words (202

migratable words and 115 nonmigratable words) again yielded no significant difference

between migrations in migratable and nonmigratable words, χ2 = 0.10, p = .76: AE made 30%

migration errors on the migratable words and 29% on the nonmigratable words.

For the second analysis, we analyzed the errors in migratable 5-letter words for which

some middle-letter migrations yield a word and some yield a nonword. For each 5-letter

migratable word that AE wrote with an error, we counted how many potential middle-letter

migrations (out of the possible 5) create a word, and how many create a nonword. This

yielded the chance rate for lexical letter position error. We then compared the rate of lexical

to nonlexical errors with this expected rate. The results indicated that 42% of the errors

yielded a word, whereas the calculated potential for a lexical error was 45%. Thus, AE’s rate

of migration errors that yielded an existing word did not differ from the rate expected by

chance, χ2 = 0.17, p = .68.

We can thus conclude that AE did not make more lexical errors than expected by chance:

he did not make more errors on migratable words, for which a migration creates an existing

word, than on nonmigratable words. In addition, even in words where lexical migrations are

possible, AE did not necessarily choose the lexical migration, and his rate of writing an

existing word was not higher than expected by chance. This lack of lexicality effect supports

a postlexical source for AE’s dysgraphia.

4.4. Are AE’s errors affected by the frequency of the target word?

Another way to examine a lexical influence on AE’s writing is to analyze whether AE’s

writing errors are affected by frequency. Such an effect would be manifested by the tendency

to succeed in writing more frequent words and to make more errors as the words become less

frequent.

The effect of frequency on AE’s writing errors was analyzed in the written naming task

and in the dictation tasks. The frequency of the 100 words in the SHEMESH naming task was

evaluated by 75 native speakers of Hebrew on a scale between 1 (unfamiliar) and 7 (very

frequent). The words ranged in frequency between 2.40 and 6.84 (M = 4.9, SD = 1.05). Using

a point-biserial correlation, we calculated whether the frequency of a word and AE’s success

or failure in writing it were correlated. The results showed no frequency effect on AE’s

writing, Rpb = 0.1, p = .33. We obtained very similar results when we correlated AE’s

Letter position dysgraphia 17

responses with the written frequency counts of Frost and Plaut (2005), Rpb = 0.1, p = .31.

The frequency of the target words in the dictation tasks (taken from Frost and Plaut,

2005) also yielded no correlation with migration errors, Rpb = 0.03, p = .22. Similar absence

of correlations was obtained when only the extremely low-frequency words, below 4

occurrences per million, and the extremely high-frequency words, above 200 per million,

were included in the analysis, Rpb = 0.05, p = .19.

4.5. Interim summary: A deficit in the graphemic output buffer

The error types, the distribution of errors within words, and the effects that modulate AE’s

writing all point to the same conclusion: AE’s writing disorder results from a deficit in the

graphemic output buffer. This is shown by his types of errors, which are characteristic of

graphemic buffer dysgraphia, and the lack of other types of errors; by the fact that these

errors occur in different output modalities (writing, typing) and in different input modalities

(dictation, written naming), and in both words and nonwords; by the distribution of errors in

middle positions; and by the significant length effect on writing and the lack of lexicality and

frequency effects on writing. The dominance of letter position errors indicates the existence

of a separate letter position function in the graphemic buffer.

5. Do Letter Position Errors Occur in Reading as Well?

The next issue we explored was whether the letter position errors evinced in AE’s writing

were also characteristic of AE’s reading. Comparing the pattern of AE’s writing with his

reading can shed light on an open question: do reading and writing make use of the same

letter-position-encoding mechanism? If so, we would expect AE to show letter position errors

in reading as well. If, however, encoding of letter position in reading occurs in the early stage

of reading, in the visual-orthographic analysis system (Ellis, 1993; Ellis et al., 1987; Ellis and

Young, 1988; Friedmann and Gvion, 2001, 2005; Friedmann and Rahamim, 2007), and if

serial selection of letters in writing occurs in a separate graphemic output buffer, then reading

and writing can show dissociable patterns, and AE’s reading would not necessarily exhibit

letter position errors.

5.1. Reading of single words

The list of 147 single words from the TILTAN screening test that was dictated to AE for

writing was presented to him for reading aloud, without time limitation. Responses were

tape-recorded and transcribed by the two authors at the time of testing. AE read 137 out of

Letter position dysgraphia 18

the 147 words (93%) correctly. His errors in reading were mainly morphological: 9 errors

involved omission or substitution of affixes, and 1 error involved reading via grapheme-to-

phoneme conversion. Thus, AE’s reading differs significantly from his writing in two

respects: his reading is significantly better than his writing, χ2 = 27.04, p < .0001, and the

pattern of errors is completely different. Whereas in writing he makes primarily letter

position errors, his reading displays mainly morphological errors and, crucially, no letter

position errors (see Fig. 2).

5.2. Reading of migratable words

To be sure that AE’s reading does not include letter position errors, we used the type of

stimuli that have been found to be most sensitive to letter position dyslexia. Friedmann and

Gvion (2001; see also Friedmann, Dotan, and Rahamim, in press; Friedmann and Rahamim,

2007; Friedmann and Haddad-Hanna, in press) reported that migratable words induced the

highest rate of letter position errors (probably because a lexical constraint on errors cannot

salvage the reading of these words). We therefore presented a list of 168 migratable words to

AE, thinking that if he had any type of letter position dyslexia in reading, it would be exposed

in this test. The list included 102 words with a lexical potential for both exterior- and middle-

letter migration, 28 words with a lexical potential for exterior-letter migration, and 38 words

with a lexical potential for middle-letter migration.

Results

AE read 134 of the 168 migratable words (80%) correctly. Only 2 of his errors were letter

position errors, a letter position error rate that does not differ from that of healthy readers of

Hebrew when they read migratable words, t(11) = 0.07, p = .90. The rest of his errors were

non–letter position errors: 28 morphological errors (82% of the total errors); 2 errors

involving the vocalic pattern of words, which resulted from reading via grapheme-to-

phoneme conversion; and 2 visual errors.

Notice that the screening reading test reported in Section 5.1 also included migratable

words – 75 words with a potential for middle-letter migration, and 56 words with a potential

for exterior-letter migration – and AE read them all without letter position errors as well.

These results, summarized in Fig. 2, further indicate that AE did not have a letter position

impairment in reading, and that his reading was mostly affected by morphological complexity

of the word stimuli.

Letter position dysgraphia 19

5.3. Reading of words with doubled letters

Also characteristic of letter position dyslexia (besides letter position errors) is the omission of

one instance of a letter that appears twice in a word. As we have noted, AE did not make

letter position errors in reading. To conclude unequivocally that he had no letter position

dyslexia, we tested whether he omitted instances of doubled letters in reading. We presented

114 words to AE, half of which included a doubled letter (not a geminate, and not necessarily

in adjacent positions) and half of which were control words. Control words were identical to

the tested doubled-letter words, except that a different letter replaced one instance of the

doubled letter. For example, we presented the word מחבבת (mexabevet ‘likes-feminine’),

which becomes מחבת (maxvat ‘pan’) when one instance of the letter ב is omitted, and the

control word מחברת (maxberet ‘notebook’ or ‘author-feminine’). The words were presented

in random order, and AE was asked to read them aloud, without time limitation.

Results

AE read 96 out of the 114 words (84%) correctly. He did not make any error of omitting one

instance of a doubled letter (but he did make 18 morphological errors). Again, these results

indicated that AE does not have a letter position dyslexia.

5.4. What is the nature of AE’s reading impairment?

The data on AE’s reading so far indicated no letter position disorder. They further indicated

that most of his errors in reading, 88%, were morphological. As Fig. 2 shows, a very clear

double dissociation emerged between reading and writing: AE’s writing includes mainly

letter position errors and few morphological errors, and his reading shows the reverse pattern,

with mainly morphological errors and no letter position errors.

Fig. 2 - Percentage of letter position errors and morphological errors out of the total number of errors in writing and in reading.

Letter position dysgraphia 20

An examination of AE’s reading of 379 morphologically complex words (created from

the three lists described in Sections 5.1–5.3 and 50 additional words with prefixes) indicated

that his morphological errors did not result from a left-neglect dyslexia, because they

occurred in all word positions: he made morphological errors in prefixes on 9% of the words

with prefixes, errors in suffixes on 15% of the words with suffixes, and 6% errors involving

the vowel pattern of middle letters. Moreover, he made no non-morphological reading errors

on the left side of words. Thus, AE’s reading errors did not result from neglect dyslexia.

Finally, in reading a list of 30 nonwords, AE showed extreme difficulty. He read only 5

out of 30 nonwords correctly, and he commented that this type of list was especially hard for

him. He made substitution and omission errors, and 10 of his responses were lexicalizations.

Thus, AE’s reading revealed a completely different pattern from his writing. In reading,

he made no letter position errors, and his errors were chiefly morphological (see Fig. 2). He

made almost no errors on words that were not morphologically complex. He made no visual

errors, no neglect dyslexia errors, and no errors that could indicate reading via grapheme-to-

phoneme conversion instead of via the lexical route. Importantly, AE also did not make any

semantic errors, which indicates that his morphological errors cannot be attributed to deep

dyslexia but are probably related to phonological dyslexia. His poor reading of nonwords is

also characteristic of phonological dyslexia.

Phonological dyslexia might result from a deficit in one of the stages of the grapheme-to-

phoneme conversion route: the parser, the grapheme-to-phoneme converter (translator), or the

component that holds the phonemes for a short time and combines them to form a word (see

Temple, 1985, 1997 regarding the three functions). This last component might very well be

the phonological output buffer. A deficit in the phonological output buffer might account for

AE’s morphological errors as well as for his inability to read nonwords (Dotan and

Friedmann, 2007). Interestingly, AE is not the first to show such an association between

graphemic buffer dysgraphia and phonological dyslexia. The same association was found for

several other patients with graphemic buffer dysgraphia (Annoni et al., 1998; Caramazza et

al., 1996; Caramazza and Miceli, 1990; Cotelli et al., 2003; Jónsdóttir et al., 1996; Sage &

Ellis, 2004; Schiller et al., 2001). The cooccurrence of graphemic buffer disorder and

phonological dyslexia might result from a deficit in the two output buffers, the graphemic

output buffer and the phonemic output buffer, possibly implying that output buffers share

resources.

Letter position dysgraphia 21

6. Is the spared letter position encoding in reading used to monitor the

impaired writing?

The dramatic difference between the relatively spared letter position encoding in AE’s

reading and his abundance of letter position errors in writing led us to explore whether AE

used his reading to monitor his impaired writing and reduce letter position errors.

To empirically address this question, we compared AE’s writing in standard conditions,

when he was able to see what he was writing, with his writing of the same words when he

lacked visual feedback. We assessed writing without visual feedback in two ways. First, we

asked AE to write on a graphic tablet (WACOM Graphire4 XL) that displayed his writing on

a computer screen that was visible to the experimenters but not to AE himself. Second, a less

high-tech method but apparently just as efficient, we placed a sheet of carbon paper between

two sheets of white paper and asked AE to write on the top sheet with an inkless pen that did

not leave marks (so we could see after the session what AE wrote, but he could not see what

he was writing as he was writing).

We compared AE’s writing performance on 168 migratable words in the standard

writing-to-dictation condition with his writing of the same words when he lacked visual

feedback. He wrote 88 of the words on the graphic tablet and 80 with the carbon paper.

Results

The graphic tablet and the carbon-paper technique yielded the same error rate, χ2 = 0.008,

p = .93, and we therefore combined the two results for further analysis. When we compared

AE’s first responses to the 168 words with and without visual feedback, we found no

significant difference between the two writing conditions. AE wrote 95 words (57%)

correctly with visual monitoring and 103 words (61%) without visual monitoring.

Two points are important here. First, when we analyzed the number of times AE tried to

correct his spelling, we found that he made significantly more correction attempts when

visual monitoring was available to him (36 times in the visual-monitoring condition

compared with only 8 times in the no-visual-monitoring condition, χ2 = 20.52, p < .01).

Second, although AE was able to use his reading in the visual-monitoring condition to realize

that he wrote letters in a particular word in the wrong order, and although he consequently

tried to rewrite the word, only 12 out of 36 corrections yielded correct results.

The results thus show that AE’s relatively spared reading may enhance the monitoring of

his writing, leading to more correction attempts, but since the correction attempts are still

made via the impaired graphemic buffer, a correct result is not necessarily achieved.

Letter position dysgraphia 22

7. Discussion

AE clearly demonstrates graphemic buffer dysgraphia, but of a very specific subtype: letter

position dysgraphia. Analysis of his error types and the effects on his writing shows that his

deficit lies in the letter position function of the graphemic buffer. He makes mainly letter

position errors in writing, across tasks and across modalities. His pattern of writing and

reading has two main implications. First, it supports the existence of a separate tier encoding

letter position, which guides serial letter selection from the graphemic output buffer,

dissociable from the letter identity activation function. Second, the dissociation between AE’s

impaired letter position encoding in writing and intact letter position encoding in reading

indicates that letter position encoding in reading and letter position encoding in writing use

two different mechanisms.

7.1. A selective impairment in serial selection

7.1.1. Error analysis

AE made 27% letter position errors in spelling and only 2% letter identity errors (omission,

substitution, or addition). McCloskey et al. (1994, see also Buchwald and Rapp, 2004; Rapp

and Kong, 2002) suggested an elaboration of the structure of the representations in the

graphemic buffer proposed by Caramazza et al. (1987) and Caramazza and Miceli (1990).

According to McCloskey et al. and Rapp et al.’s suggestions, the graphemic buffer has two

distinct functions: letter identity - activating the constituent graphemes of a word, and letter

position - serially selecting the individual graphemes from the set of active letters. Each of

these functions can be selectively damaged, resulting in two distinct types of graphemic

buffer deficits. Indeed, two varieties of graphemic buffer dysgraphia have been reported: a

selective deficit in the activation component was reported for RSB and BWN, and a selective

deficit in the serial selection function was reported for JRE (Buchwald and Rapp, 2004; Rapp

and Kong, 2002). These patients differed in their sensitivity to lexical frequency (only the

patients with the activation deficit were sensitive), and in their ability to judge whether a

letter exists in a word or not (a task in which only the patient with the serial selection deficit

succeeded).

Crucially, the current case study of AE supports the dissociability of letter activation and

serial selection from an additional angle. It shows that the two functions differ not only with

respect to frequency effects and performance in the probe task, but also with respect to the

types of errors they entail. A selective deficit in the letter activation component of the buffer

entails letter identity errors such as substitutions, omissions, and perhaps additions. When the

Letter position dysgraphia 23

impairment affects the serial selection function, letter position errors occur.

Individuals with graphemic output dysgraphia who make selectively letter identity errors

have been reported. In the case described by Cotelli et al. (2003), the deficit is specific to

vowels, with predominantly vowel substitution errors (80%) and no letter position errors.

Posteraro et al. (1988) report an individual whose errors predominantly involved omission of

letters, both vowels and consonants (75% on various written tasks), but who made no letter

position errors. Baxter and Warrington (1983) report on ORF, who had phonological and left-

neglect dysgraphia that caused substitutions, omissions, and additions of initial left-side

letters, but who made no letter position errors. Kay and Hanley (1994) and Hanley and Kay

(1998) also report an individual who made letter identity errors and almost no letter position

errors (3%). Although the dysgraphia is not manifested uniformly in these individuals, from

the errors they display it is nonetheless evident that letter identity representations are

sensitive to the consonant-vowel distinction, the syllabic organization of the graphemic

structure, and gemination (Buchwald and Rapp, 2003; Caramazza and Miceli, 1990; Cubelli,

1991; see Miceli and Capasso, 2006 for a review).

Other studies report graphemic buffer disorders that cause both letter identity errors and

letter position errors (Annoni et al., 1998; Buchwald and Rapp, 2003; Caramazza et al., 1987;

Caramazza and Miceli, 1990; Jónsdóttir et al., 1996; McCloskey et al., 1994; Tainturier and

Caramazza, 1996; Tainturier and Rapp, 2004).

An individual who made significantly more letter position errors than letter identity errors

was reported by Blanken et al. (1999). This study is important because it was a clear case of

this particular pattern, of more letter position errors than letter identity errors, albeit with a

small error rate (less than 8%) in writing to dictation. The current case study of AE, who

made 27% errors of letter position and only 2% errors of letter identity, gives this dissociation

a boost, and further supports the approach suggested by McCloskey et al. (1994), Rapp and

Kong, 2002, and Buchwald and Rapp, 2004, according to which the graphemic buffer is

responsible for two separate functions: letter identity and letter position.

AE’s deficit is clearly located in the graphemic buffer and not in an earlier stage, as

indicated by the types of errors he made in writing: mainly letter position errors and some

letter identity errors, but no semantic errors and no regularization errors or errors involving

homophones. The findings that AE’s letter position errors appeared across spelling outputs –

in handwriting and in typing – and that he made no errors of letter formation and no

significant errors in immediate copying indicate that his deficit cannot be located in a stage

later than the graphemic buffer. His similar error pattern in nonwords and in words indicates

Letter position dysgraphia 24

that the deficit does not reside in the orthographic input lexicon but rather in the stage that is

shared by words and nonwords, the graphemic buffer. That AE’s deficit is located in the

graphemic buffer is also indicated by the effects on his writing, to which we now turn.

7.1.2. Effects on writing

Analysis of various effects on AE’s writing sheds additional light on the characteristics of

this subtype of graphemic buffer dysgraphia.

Length effect. AE’s writing was dramatically affected by the number of letters in the target

words; longer target words yielded more letter position errors. This finding is in line with

other studies of graphemic buffer dysgraphia that reported a length effect (Baxter and

Warrington, 1983; Blanken et al., 1999; Buchwald and Rapp, 2003, 2004; Caramazza et al.,

1987; Cotelli et al., 2003; Glasspool and Houghton, 2005; Hanley and Kay, 1998; Jónsdóttir

et al., 1996; Kay and Hanley, 1994; Miceli et al., 1997, 2004; Posteraro et al., 1988; Rapp,

2005; Rapp and Kong, 2002; Schiller et al., 2001; Tainturier and Rapp, 2004). This effect

probably results from the nature of the graphemic buffer as a temporary memory store, and it

supports locating AE’s deficit in the graphemic buffer stage.

No frequency effect. Rapp and her colleagues (Rapp and Kong, 2002; Buchwald and Rapp,

2004) reported that their participant with letter activation impairment showed a frequency

effect when the extremes of the frequency range were contrasted. On the other hand, AE –

like Rapp and colleagues’ other participant, who had a serial selection deficit, and like LM,

who made mainly letter position errors (Blanken et al., 1999) – was not affected by the

frequency of the target word. It might be, then, that whereas the activation stage of the

graphemic buffer is still sensitive to the frequency of the target word – possibly because

activation at the graphemic buffer stage is directly related to activation from the lexicon,

which is larger when a word is more frequent – the serial selection stage is no longer affected

by frequency. This might also support the view that these two stages are organized serially

(Buchwald and Rapp, 2004) – that is, graphemes are first activated and then ordered. The first

stage, the letter identity stage, keeps the graphemes in the word activated. The second stage,

the letter position stage, keeps the information about the relative order of the letters (in a way

that gives a special status to the first and final letters). The letter position deficit in spelling

can result either from a deficit in letter position information within the buffer, or in the order

of serial selection of letters from the buffer for writing.

No lexicality constraint on the response. The analysis of the lexical status of AE’s errors

Letter position dysgraphia 25

showed that lexicality did not constrain his writing errors. The incorrect sequences that he

wrote distributed between lexical and nonlexical responses at a rate expected by chance. This

finding is in line with previous reports on graphemic buffer dysgraphia (Blanken et al., 1999;

Cotelli et al., 2003; Posteraro et al., 1988; Rapp and Kane, 2002; Tainturier and Caramazza,

1996; Tainturier and Rapp, 2004).

No migratability effect. Related to the absence of a lexicality constraint on AE’s writing

errors is the finding that his writing was also not affected by the migratability of the target

word, i.e., whether or not letter migration within the word creates another existing word.

Errors occurred in both migratable and nonmigratable words. Moreover, even in words that

had a potential for lexical migrations, the lexical migration option was not necessarily the one

that was selected; sometimes the letters moved to positions that created nonwords. This is in

marked contrast to what happens in letter position dyslexia, where migratable words are

significantly more susceptible to letter position errors than nonmigratable words (in both

acquired letter position dyslexia, Friedmann and Gvion, 2001, 2005, and developmental letter

position dyslexia, Friedmann and Rahamim, 2007). This difference is not surprising: in

reading, when letter position encoding is impaired, the reader can rely on the lexicon, leading

to better reading of nonmigratable words than of migratable words, but because the

graphemic buffer is a postlexical stage, when it is impaired writing can no longer benefit

from or be affected by the lexicon.

Exterior-letter advantage. One of the robust findings in the reading of individuals with

acquired or developmental letter position dyslexia is that middle letters are much more

susceptible to letter position errors than exterior letters are, and that first and last letters are

relatively migration proof (Friedmann and Gvion, 2001, 2005; Friedmann and Rahamim,

2007). AE’s spelling shows a similar exterior-letter advantage. Middle letters migrated 10

times more often than first and last letters. Blanken et al. (1999) reported the same for LM,

who made more errors in middle than in exterior letters (with the exception of 3-letter words,

where the rates of migration for middle and final letters were similar).6 This exterior letter

6 Note that the middle position of the error in letter position dysgraphia is not characteristic only of a selective deficit in serial selection in the graphemic buffer. Middle-letter susceptibility to errors was also reported in some individuals who made mainly letter identity errors (Buchwald and Rapp, 2004; Posteraro et al., 1988) and in individuals who made both letter identity and letter order errors (Caramazza et al., 1987; Caramazza and Miceli, 1990; Jónsdóttir et al., 1996; Tainturier and Caramazza, 1996; see Glasspool and Houghton, 2005 and Glasspool et al., 2006 for a review and analysis of the serial position of various error types). Still other individuals with deficits in both letter identity and letter position in the graphemic buffer made errors mainly in one side of the word (Baxter and Warrington, 1983; O’Dowd and de Zubicaray, 2003; Schiller et al., 2001; see Miceli and Capasso, 2006 for a review).

Letter position dysgraphia 26

advantage suggests that, like in reading, the first and final letters have a special status and

their position is encoded separately.

7.2. Letter position encoding in reading and writing

AE’s writing and reading demonstrated a very clear dissociation between letter position

encoding in writing and letter position encoding in reading. Whereas AE made letter position

errors in writing, he made no letter position errors in reading. This dissociation indicates that

letter position encoding in the input orthographic-visual analyzer (or the component referred

to as the “prelexical graphemic buffer” by Caramazza et al., 1996) is a separate function from

the serial-letter-ordering function in the graphemic buffer.

AE’s reading of real words was only mildly impaired (86% correct), and his difficulty

was reflected mainly in morphological errors in real words and in a significant difficulty with

reading nonwords. Crucially, his reading did not include letter position errors, even in the two

types of stimuli that cannot make use of lexical compensation: migratable words and

nonwords.

This result has important implications for the relation between letter position encoding in

reading and letter position encoding in writing. It suggests that the letter-position-encoding

function in the orthographic-visual analysis system is different from the serial selection

function of the graphemic buffer (in line with Shallice et al.’s, 2000 suggestions with respect

to the separation between input and output phonological buffers).

These data, showing a dissociation between impaired letter position in writing and intact

letter position in reading, combine with recent data from developmental letter position

dyslexia to form a double dissociation. Friedmann and Rahamim (2007) showed that six

children with developmental letter position dyslexia, who made 14%-45% letter position

errors in reading, did not make letter position errors in writing.

AE’s relatively spared reading of words was found to play an important role in

monitoring his writing output. When AE could visually monitor his work, he noticed that he

wrote the words incorrectly, and consequently made significantly more correction attempts,

compared with trials when he could not see what he wrote. These attempts did not necessarily

result in correct spelling because he again had to go through his impaired graphemic buffer.

In their review of graphemic buffer deficits, Miceli and Capasso (2006) conclude that

there is no single, homogeneous graphemic buffer deficit and that there is more to be learned

about the graphemic buffer’s structure and functions. AE’s pattern of spelling further shows

how relevant the data from neuropsychology are for developing the cognitive model of

Letter position dysgraphia 27

spelling. AE’s specific pattern of writing, his letter position dysgraphia, indicates the

existence of a special function in the graphemic buffer that is responsible for the encoding of

letter position. This function can be damaged selectively, separately from the letter identity

function of the graphemic buffer, and separately from the letter-position-encoding function in

reading.

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Appendix A

T1 MRI scan of AE’s brain