Developmental surface dyslexias - Naama Friedmann

cortex 44 (2008) 1146–1160 

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Research report 

Developmental surface dyslexias 

Naama Friedmann* and Limor Lukov 

Language and Brain Lab, School of Education, Tel Aviv University, Tel Aviv, Israel 

article info 

Article history: 

Received 18 June 2007 

Reviewed 13 August 2007 

Revised 26 August 2007 

Accepted 5 September 2007 

Action editor Roberto Cubelli 

Published online 5 March 2008 

Keywords: 

Surface dyslexia 

Dual route model 

Hebrew 

Developmental dyslexia 

abstract 

Individuals with surface dyslexia read via grapheme-to-phoneme conversion due to a deficit 

in the lexical route. A deficit in the lexical route can be caused by impairments at several 

different loci. In the current study we identify three subtypes of developmental surface 

dyslexia, each caused by impairment at a different locus on the lexical route, and each 

showing a different pattern of performance in various tasks. All three subtypes show the 

classical pattern of reading aloud, with regularizations and difficulty in reading words 

that have more than a single possible conversion to a phoneme string, but they differ in 

their performance in lexical decision and homophone comprehension. The first subtype, 

input surface dyslexia, results from a deficit to the orthographic input lexicon, and entails 

poor performance in lexical decision and comprehension tasks. The second subtype, orthographic 

lexicon output surface dyslexia, in which the orthographic input lexicon is accessible 

but its output to the phonological output lexicon and to the semantic system is impaired, 

allows normal lexical decision, but causes impaired comprehension of homophones. The 

third subtype, interlexical surface dyslexia, caused by a selective deficit in the connection between 

the orthographic input lexicon and the phonological output lexicon but with intact 

access from the orthographic input lexicon to the semantic system, allows normal performance 

in lexical decision and comprehension tasks. Seventeen Hebrew-speaking individuals 

with developmental surface dyslexia aged 10–43 participated in the study, eight of 

them showed the first pattern, three showed the second pattern, and six displayed the 

third pattern. Another result of the study pertains to the importance of the lexicality of 

the result of grapheme-to-phoneme conversion for each target word. Some words, when 

read via grapheme-to-phoneme conversion, can potentially be read as other words (such 

as ‘‘now’’ in English, which can be sounded as the word ‘‘know’’), we term these words potentiophones. 

The results indicate that potentiophones yield the highest error rate in reading 

aloud for all the participants with surface dyslexia. 

ª 2007 Elsevier Srl. All rights reserved. 

1. Introduction 

The definition of surface dyslexia relates to the way individuals 

with this dyslexia read: they read via graphemeto-phoneme 

conversion. But why do they read via this 

route? Which part of the lexical route is impaired? This definition 

does not specify which component of the reading 

process is impaired. A look at the dual-route model for 

reading suggests that several different impairments to various 

parts of the lexical route can cause surface dyslexia. In 

* Corresponding author. Language and Brain Lab, School of Education, Tel Aviv University, Tel Aviv 69978, Israel. 

E-mail address: naamafr@post.tau.ac.il (N. Friedmann). 

0010-9452/$ – see front matter ª 2007 Elsevier Srl. All rights reserved. 

doi:10.1016/j.cortex.2007.09.005

cortex 44 (2008) 1146–1160 1147 

the current study we focus on developmental surface dyslexia 

and show that at least three different loci on the lexical 

route can be impaired, causing three different subtypes 

of developmental surface dyslexia, which differ in the patterns 

of performance in various tasks. 

When the lexical route is unavailable, readers may be 

forced to rely on the grapheme-to-phoneme route for oral 

reading. Looking more closely into what can cause the lexical 

route to be unavailable, several possible loci of impairment 

emerge: one might be the orthographic input lexicon 

or the access to it ( in Fig. 1). Another possibility is that 

the orthographic input lexicon itself is intact and accessible, 

but its output is damaged: either its output both to 

the phonological output lexicon and to the semantic system 

(marked in Fig. 1), or only the output to the phonological 

lexicon (marked in Fig. 1), with intact access to the semantic 

system. 

Grapheme-to-phoneme reading can also result from an 

impairment to the semantic system, to the phonological output 

lexicon, or its access to the phonemic output buffer (Jackson 

and Coltheart, 2001) but in these cases, surface dyslexia is 

part of a more general language or semantic impairment, and 

is not restricted to reading, and we will not explore these subtypes 

in the current study. 

The three impairments (1–3 in Fig. 1) are expected to 

yield a similar pattern of reading aloud. Since all three impairment 

loci cause reading via conversion rules, all three 

impairments should result in regularizations in reading 

aloud. However, importantly, the three impairments are 

expected to differ with respect to their effect on lexical decision 

and comprehension. The first impairment – involving 

lack of access to the orthographic input lexicon, or impaired 

orthographic input lexicon 1 – would result both in 

difficulty in lexical decision and in impaired comprehension. 

Namely, this deficit will result in inability to determine 

whether a letter string forms an existing word, 

especially when it can be sounded out via grapheme-tophoneme 

conversion as an existing word. The comprehension 

in this type of impairment will rely solely on the 

phonological output of the grapheme-to-phoneme conversion. 

Thus, words that are regular and nonhomophonous might 

be understood correctly, but irregular words and homophones 

would either not be recognized as a word and 

thus not be understood, or be recognized as a different 

word and misunderstood. For example, if a word like 

‘‘yacht’’ would be read as yakt, the reader might say that 

she does not recognize the word. A word like ‘‘sale’’, 

when identified solely on the basis of the phonological lexicon, 

might be defined as ‘‘To move along the sea with 

a boat’’, and a word like ‘‘too’’ might be defined as ‘‘The 

number after one’’. 

Individuals with an impairment of the second subtype – 

impaired connection from the orthographic input lexicon to 

both the phonological output lexicon and the semantic 

1 Ascribing a deficit to the orthographic input lexicon still leaves 

the question open whether the deficit is in processes operating in 

and on the lexicon, or whether the representations in the lexicon 

are impaired (for example, ‘‘faded’’, and require additional activation 

to be accessed). 

semantics 

orthographic-visual analysis: 

letter identification letter position letter-word binding 

2 

orthographic 

input lexicon 

2 

1 

3 

phonological 

output lexicon 

phonemic buffer 

grapheme-to-phoneme 

conversion 

Fig. 1 – A model of single word reading. The numbers 

indicate possible loci of impairment that lead to 

developmental surface dyslexia. 

system – are expected to be able to decide whether a letter 

sequence is a word or not, even when it is a pseudohomophone, 

as they have access to the orthographic input lexicon. 

Because they do not have access to semantics, they 

will fail in comprehension in much the same way as the 

first subtype. 

Finally, individuals with an impairment of the third subtype 

– whose impairment results from a disconnection between 

the orthographic input lexicon and the phonological 

output lexicon – are expected to perform well both in lexical 

decision tasks and in comprehension tasks, when these tasks 

do not involve oral reading. This is because they have intact 

access to the orthographic input lexicon and from it to the 

semantic system. Only when they read aloud will their surface 

dyslexia be manifested, because they will be forced to 

use the grapheme-to-phoneme route. 2 

Thus, in order to determine the locus of impairment for 

each individual with surface dyslexia, reading aloud is not 

enough. The performance in lexical decision, and specifically 

the ability to reject pseudohomophones (nonwords 

that can be sounded out like real words, such as fone), would 

indicate whether the orthographic input lexicon is accessible. 

Comprehension tasks of homophones might speak for 

whether or not there is access to the semantic system 

from the orthographic input lexicon (Marshall, 1984a). 

In a seminal study of acquired surface dyslexia, Coltheart 

and Funnell (1987) identified seven loci that might 

lead to acquired surface dyslexia. They showed that their 

2 Theoretically, when the pathway between the lexicons is impaired, 

one can also use the route from semantics to the phonological 

output lexicon in order to read aloud. However, whereas 

this route is the natural route for word retrieval, it does not 

seem to be a natural route for reading, and this is why the arrow 

appears dashed in Fig. 1. It seems to be a last resort, used only 

when no other route is available for reading, as is the case in 

deep dyslexia. We will return to this point in the Discussion, on 

the basis of our results. 

1

1148 

cortex 44 (2008) 1146–1160 

patient, HG, had surface dyslexia that resulted from a deficit 

in the orthographic input lexicon (in entries within it or in 

the access to it). Other individuals with a similar impairment 

to the orthographic input lexicon are NW, reported 

by Weekes and Coltheart (1996), and EE, reported by 

Howard and Franklin (1987) and Coltheart and Byng (1989) 

(although EE also had considerable output impairments). 

Their locus of impairment was identified on the basis of 

poor reading of irregular words, poor lexical discrimination 

(in which participants were asked to select the word in 

word/pseudohomophone pairs), and poor homophone comprehension. 

A recent report of MM, a Spanish-speaking individual 

with surface dyslexia, also described a deficit to 

the input lexicon (Ferreres et al., 2005). The patients described 

by Marshall and Newcombe, JC and MS (Marshall 

and Newcombe, 1973; Newcombe and Marshall, 1981, 

1984, 1985) also fit the description of an impaired orthographic 

input lexicon (JC is taken to be such a case, although 

data are available only with respect to his 

impaired reading of irregular words and his impaired comprehension 

of homophones; see Ellis et al., 2000). 

Another subtype of acquired surface dyslexia that has 

been reported in the literature is central or semantic surface 

dyslexia, which was described as resulting from a deficit 

to the semantic system. Such cases are HTR (Shallice 

et al., 1983), MP (Bub et al., 1985), KT (McCarthy and Warrington, 

1986; Patterson and Hodges, 1992), and JL and GC 

(Graham et al., 1994). Notice, however, that if only the semantic 

system was impaired in these cases, it is not clear 

why the patients did not use the direct lexical route to 

read irregular words, but rather the sublexical route. A lesion 

that is restricted to the semantic system does not suffice 

to account for reading via the sublexical route, 

especially given reports in the literature of individuals 

with severely compromised comprehension whose reading 

of irregular words was unimpaired (cf., Blazely et al., 

2005; Cipolotti and Warrington, 1995; Schwartz et al., 1979, 

1980), so an additional impairment might be responsible 

for the inability to read via the direct lexical route. 

One other subtype of acquired surface dyslexia reported is 

sometimes termed ‘‘output surface dyslexia’’. These are typically 

cases of individuals with impaired naming and impaired 

phonological output lexicon, who succeed in written word 

comprehension and lexical decision. Such patients are EST 

(Kay and Ellis, 1987; Kay and Patterson, 1985), MK (Howard 

and Franklin, 1987), and FM (Graham et al., 1994). Their deficits 

are in the phonological output lexicon or in its output to the 

phonemic buffer. 

Notice, however, that the latter two subtypes described 

in the literature, semantic and output surface dyslexia, 

are in fact not selective types of surface dyslexia but are 

rather cases of impairment to components that are not specific 

to reading, the semantic system or the phonological 

output lexicon. Only the first subtype, in which the orthographic 

input lexicon is impaired, is specific to reading. 

The two other options we described (marked and in 

Fig. 1) are different – they relate to impairments in the connection 

from the orthographic input lexicon to the semantic 

system and the phonological output lexicon, which are 

still part of the reading process. The disconnections we 

described can appear without a deficit to comprehension 

of auditorily presented words and without naming deficits. 

As far as we know, whereas cases of developmental surface 

dyslexia were reported in the literature (Broom and 

Doctor, 1995a; Castles et al., 2006; Castles and Coltheart, 

1993, 1996; Coltheart, 1987; Coltheart et al., 1983; Judica 

et al., 2002; Masterson, 2000; Temple, 1997), and whereas, 

on the basis of the reading model, subtypes are expected 

in developmental surface dyslexia as well (Castles, 2006), 

until now no study identified subtypes in the developmental 

form of surface dyslexia. In the current study we examine 

whether such subtypes also exist in developmental 

surface dyslexia. We test reading in Hebrew, which, due 

to its extremely irregular orthography, is a very good testing 

ground for surface dyslexia, and a very easy language 

to identify this dyslexia. 

1.1. A bit about Hebrew 

When is reading via grapheme-to-phoneme conversion especially 

problematic? When many written words cannot be converted 

to a unique phoneme string. Hebrew is exactly such 

a language, in which no word can be converted unambiguously 

to phonemes. 

Hebrew is a Semitic language, read from right to left. It has 

22 letters, nine of them with ambiguous conversion to phonemes 

– four that can be mapped onto two different consonantal 

sounds, and five letters that can serve either as 

a vowel (or several vowels) or as a consonant (see Appendix 

A). This is the first source of ambiguity in reading via grapheme-to-phoneme 

conversion in Hebrew. Another source is 

the under-representation of vowels. The vowels /a/ and /3/ 

are almost never represented in writing (except for at the 

end of words, where they are both represented by the same 

letter), with the result that words that sound completely different 

are written exactly the same way. For example, /sefer/ 

(book), /safar/ (counted), and /sfar/ (frontier) are all written 

SFR, ; /meter/ (meter) and /matar/ (rain) are both written 

MTR, ; and KRX, , stands for both /kerax/ (ice) and 

/kere’ax/ (bald). The vowels /i/, /o/, and /u/ are represented 

only in some of the words. Even when a vowel is represented 

orthographically by a letter, this letter is usually ambiguous 

between several vowels and consonants (the letter ‘‘ ’’, for example, 

can be read as /o/, /u/, or /v/). Thus, a word can comprise 

only consonant letters (even 7 and 8-letter words like 

HTPRSMTM, /hitparsamtem/, and MTGLGLT /mitgalgelet/), 

and the vowels and the stress should be added in reading 

based on orthographic–lexical knowledge of the word, or 

some frequency preferences. Furthermore, stress is not represented 

in the orthography, and stress position in Hebrew is 

lexically specified (Bat-El, 1993), so the word XRS, can 

be read both with an initial stress, /xeresh/ (silently), and 

with final stress, /xeresh/ (deaf) (as well as /xarash/, plowed). 

This means that irregularity takes a wider sense in the case of 

Hebrew: it is not only the case that a letter or a group of letters 

can be converted into more than a single sound, but also that 

the lack of letters (mainly vowel letters) creates ambiguity 

with respect to conversion to sound. 

The result of these properties of Hebrew orthography is 

that in fact no word can be read unambiguously via

cortex 44 (2008) 1146–1160 1149 

grapheme-to-phoneme conversion, although some conversions 

might be favorable. Even 3-letter words might theoretically 

have several thousands of possible readings. For 

example, in the word , QBS, each of the three letters can 

be converted to either of two consonants, and the vowels 

are not represented, so after each consonant letter one of six 

vowels can be used. Together with the two possible stress positions, 

this leads to 2 2 2 6 6 6 2 ¼ 3456 theoretical 

ways to read this word, which the orthographic lexicon narrows 

down to three lexical options. 

Another result of this structure of Hebrew orthography that 

is important for the description of surface dyslexia is the abundance 

of potentiophones (Gvion and Friedmann, 2001; Lukov and 

Friedmann, 2006). We use the term potentiophones for word 

pairs that are written differently and sound differently, but 

whose letter sequence can be mapped onto the same sound 

string. Therefore when such a word is read solely via grapheme-to-phoneme 

conversion, it can be read aloud as the other 

existing word, which sounds differently. An example in English 

is the word now that can be read as no or know when read 

via grapheme-to-phoneme conversion (other examples for 

English potentiophones are resent–recent, come–comb, bear– 

beer, angle–angel, talk–talc, and whose–hose). Examples for 

potentiophones in Hebrew are the pairs (KtR–QTR, 

/katar/–/keter/, locomotive–crown), (QMO–KMO, /kmo/–/ 

kamu/, like–woke up), and (XOL–XBL, /xol/–/xevel/, sand– 

rope). 

Potentiophones are valuable for the diagnosis of surface 

dyslexia, because reading aloud of these words can already 

indicate whether or not the reader used her lexical route 

for reading. They are better for the detection of surface dyslexia 

than homophones, because homophones sound the 

same and thus reading aloud cannot indicate whether 

they were read correctly or not, and they thus require comprehension 

tasks. Furthermore, potentiophones might be 

more sensitive to surface dyslexia reading than other irregular 

words because the reading of irregular words that do 

not have potentiophones results in a nonlexical response. 

Because some individuals with surface dyslexia have 

a strong tendency to produce real words as output (Patterson 

et al., 1985, p. 12), this nonlexical response may be 

identified by the reader as incorrect, and corrected immediately 

in an attempt to reach a lexical response. An incorrect 

reading of a potentiophone, however, yields an existing 

word, and hence does not allow the detection of the 

error. 

In the current study we used these characteristics of Hebrew 

orthography to examine surface dyslexia, and more specifically 

three subtypes of developmental surface dyslexia. We 

also explored the way surface dyslexia is manifested in 

a highly irregular language like Hebrew. 

2. Experimental investigation 

2.1. Participants 

2.1.1. Participants with developmental surface dyslexia 

The participants with surface dyslexia were individuals who 

had developmental dyslexia, who were diagnosed with 

‘‘learning disabilities’’ or ‘‘reading disabilities’’ prior to the 

study. We included them in the study based on the number 

and types of errors they made in single word reading. Participants 

were included in the study only if their reading aloud 

(see Section 2.2.1) included significantly more errors than 

the control group, and the type of errors they made in reading 

were errors that result from reading via graphemeto-phoneme 

conversion: regularizations, errors in vowel 

pattern of unvoweled words or words with ambiguous vowel 

letters, and potentiophone errors. The comparison of each 

participant to her/his control group was done using the 

Crawford and Howell’s (1998) t-test for the comparison of 

a single participant to a group. 

This created a group of 17 participants, six female and 

11 male. Their background information is presented in 

Table 1. All the participants with developmental surface 

dyslexia had normal IQ, and studied in regular schools 

and regular classes. They had normal language, their spontaneous 

speech was normal and none of them was diagnosed 

with SLI (specific language impairment). Four of the 

participants (TM, OM, BZ, and YD) were tested with spoken 

language test batteries for the diagnosis of syntactic impairments 

(BAMBI, Friedmann and Novogrodsky, 2002; BAFLA, 

Friedmann, 1998), and a test battery for the assessment of 

phonological abilities (BLIP, Friedmann, 2003), showing performance 

within the norm in syntax and phonology. In order 

to avoid surface dyslexia-like reading that resulted from 

lack of sufficient exposure to reading, we only included participants 

who were in fifth grade and higher, and who had 

effective classroom instruction. Eleven of the participants 

were in fifth or sixth grade, four were in middle school, 

and two were adults. All of them had Hebrew as their 

mother tongue, and one was bilingual and had both Hebrew 

and English as mother tongues. They had no hearing 

impairment, and none of them had a history of neurological 

disease or head trauma that might have led to acquired 

Table 1 – Background information on the participants 

with developmental surface dyslexia 

Participant Age Grade Gender Handedness Remedial 

teaching 

SH 10;8 5 M R Yes 

GL 10;10 5 F R – 

OF 11;2 5 M R – 

YR 11;0 5 M R Yes 

TM 12;0 6 F R Yes 

NT 12;8 6 M R Yes 

OM 14;10 8 M R Yes 

BZ 43 Adult M R – 

AS 11 5 M R Yes 

OS 11 5 F R – 

AK 13;9 8 M R Yes 

AM 10;7 5 F R – 

AL 11 5 M R Yes 

KR 11 5 F R – 

NF 14;5 8 M R Yes 

IR 15;10 9 M L Yes 

YD 21 Adult F R Yes

1150 

cortex 44 (2008) 1146–1160 

dyslexia. As can be seen in Table 1, some of the participants 

received remedial teaching within or outside 

school. 

2.1.2. Control groups 

A total of 68 individuals without reading or language impairment 

participated as control participants. They were tested 

with the same tests in order to assess the normal level of performance 

in each test. Because the participants with surface 

dyslexia were of three age groups, fifth to sixth grade, middle 

school, and adults, we administered the tests to three groups 

of individuals without reading or language impairments to attain 

reference scores for each age: 28 individuals in fifth grade, 

24 individuals in middle school (seventh–ninth grade), and 16 

adults aged over 21. 

2.2. Methods 

2.2.1. Reading aloud 

The route the participants used for reading aloud was 

assessed using a task of reading aloud of single words. 

The list included 340 Hebrew words, 220 irregular words 

with irregularity of an ambiguous consonant or silent 

letters, 140 of them without a potentiophone and 80 with 

potentiophones, and 80 relatively regular potentiophones. 

Words were defined ‘‘relatively regular’’ when they did 

not include irregularity of ambiguous letters, silent vowel 

letters, or vowel letters with irregular sound. We called 

them relatively regular rather than regular because they 

were still, like all Hebrew words, underspecified for vowels 

and stress. Sixteen of the relatively regular words without 

potentiophones included the regular (more frequent) conversion 

of vowel letters, and a sound for underrepresented 

vowels, which is usually the preferred conversion. The list 

also included 40 relatively regular words without potentiophones, 

which were compared to the irregular and potentiophonic 

words. 

In addition, in order to assess their ability to read via the 

sublexical route, five of the participants (who were still accessible 

for additional testing) read a list of 30 pronounceable 

nonwords (from TILTAN screening test, Friedmann 

and Gvion, 2003). Twenty of these nonwords were presented 

with diacritic points indicating the voweling, and 

10 were unpointed (in the unvoweled nonwords, when no 

vowel letter was present, each vowel the participant chose 

was accepted as correct). A third of the nonwords was created 

by substitution of a single letter in existing words, 

a third by addition or substitution of the leftmost letter in 

an existing word, and another third was created by transposition 

of middle letters of an existing word. 

2.2.2. Lexical decision 

In order to test whether the participants could use the orthographic 

input lexicon even if they read the words aloud via 

the sublexical route, we used a lexical selection task. The 

task included 75 pairs of letter sequences. Each pair included 

a word spelled correctly, and its pseudohomophone (knife– 

nife for a relevant example in English). The participants 

were asked to circle the existing word (the correctly spelled 

word) in each pair. 3 The target words included irregular 

words (chef–shef, key–kee), and words with a homophonic 

letter (cinema–sinema). (Because more than half of the letters 

in Hebrew, 13 of the 22 letters, can be mapped onto the same 

sound as another letter, most of the words have a pseudohomophone, 

and most of the words need orthographic–lexical 

information for correct selection. See Appendix A.) 

2.2.3. Semantics 

For the assessment of the comprehension of homophones and 

potentiophones we used a task with triads of written words. 

The task included 40 triads, each triad including a target 

word and two words – one word was associated semantically 

with the target word, the other word was a homophone or 

potentiophone of the associated word. The participants had 

to choose the word that was semantically associated with 

the target word. For example, for the target word lettuce, we 

gave the words cabbage and near, which are potentiophones 

in Hebrew ( ; /kruv/–/karov/), and the participant had 

to choose cabbage, which was semantically related to the target 

word lettuce. (A possible example for English would be asking 

the participant to choose between the potentiophones bear 

and beer for the target word drink.) 

2.2.4. Naming 

To examine the status of the phonological output lexicon of 

our participants, we also included a task of naming 100 color 

pictures of objects (SHEMESH, Biran and Friedmann, 2004, 

2005, 2006; Friedmann and Biran, 2003). The participants 

were presented with a picture and were asked to name it 

aloud. We collected the responses, including hesitations and 

self-corrections. Hesitations longer than 5 sec and incorrect 

first responses were counted as incorrect responses. This 

task was administered to 15 of the 17 participants. 

2.2.5. Statistical analysis of comparison to the control group 

In order to determine for each score of each participant in 

each test whether it was within the normal range, we compared 

the score with the score of the relevant control group. 

Scores of participants in fifth and sixth grade were compared 

to the scores of controls in fifth grade. Scores of participants in 

seventh–ninth grade were compared to the middle school 

control group, and the scores of the two adults were compared 

to the adult control group. The comparison was done using 

Crawford and Howell’s (1998) t-test for the comparison of 

a single participant to a control group. For each task and 

3 We preferred to use a lexical selection task for a word and its 

pseudohomophone over lexical decision of single items because 

on the basis of an earlier assessment (Lukov and Friedmann, 

2006), individuals with surface dyslexia who perform flawlessly 

or almost flawlessly on lexical selection sometimes fail on lexical 

decision. This, we believe, results from the inclination or custom, 

when encountered with a letter string, to read and sound-out via 

the sublexical route. In the case of lexical decision of a pseudohomophone 

this tendency yields an existing word and thus leads to 

acceptance of the pseudohomophones as a word. However, such 

strategy cannot be employed when two items are presented, 

which both lead to the same sound. In this case, the reader is 

forced to consult the orthographic input lexicon. When this lexicon 

is available, lexical selection is successful.

cortex 44 (2008) 1146–1160 1151 

Table 2 – Percentage error in reading aloud of irregular and relatively regular words, and of words with and without 

potentiophones 

Participant 

Irregular with 

potentiophone 

Irregular no 

potentiophone 

Relatively regular 

with potentiophone 

Total irregular or 

potentiophone 

Relatively regular 

no potentiophone 

SH 37 28 45 35 8 

GL 39 31 47 38 8 

OF 29 18 34 25 8 

YR 56 48 56 52 11 

TM 50 37 60 49 9 

NT a 56 50 – 51 0 

OM 37 29 39 35 3 

BZ 21 10 46 23 0 

AS 25 18 38 26 11 

OS 44 37 56 44 3 

AK 20 18 28 22 5 

AM 23 31 45 33 11 

AL 20 13 32 20 5 

KR 21 21 31 24 3 

NF 46 28 27 33 3 

IR 11 7 23 14 6 

YD 14 3 20 12 1 

Control groups 

Fifth grade 1.5 4.3 7.8 5.0 1.6 

Middle school .9 2.2 3.8 2.5 .3 

Adults 0 .3 2.2 1.0 .1 

a NT was not tested on regular potentiophones. 

each age group we found the cut-off point beyond which the 

number of errors was already significantly larger ( p < .05) 

than the number of errors in the control group. 

2.3. Results 

2.3.1. Reading aloud 

The results of the reading aloud task, presented in Table 2, 

clearly indicate that the participants had surface dyslexia. 

They had significant difficulties in reading aloud of the target 

irregular and potentiophonic words, whereas they read the 

relatively regular words better. Each of the participants had 

significantly more errors than their matched control group 

(for the two adults, t(15) > 11, p < .001; for the four participants 

in middle school, t(23) > 6, p < .0001; for the children in fifth 

and sixth grade, t(27) > 3, p < .002). 

Their reading errors were characteristic of surface dyslexia: 

they produced errors of regularization, reading with 

the incorrect vowel when the vowel was not represented, 

reading with the incorrect mapping to sound of sound-ambiguous 

letters, and incorrect stress position (see Appendix B for 

error examples). 

Participants’ reading of irregular and potentiophonic 

words was significantly poorer than their reading of the relatively 

regular words that did not have potentiophones, 

z(16) ¼ 3.6, p ¼ .0003. 4 Importantly, whether or not a word 

had a potentiophone had a crucial effect on reading. The participants 

made more errors when the target irregular word 

had a potentiophone than when it did not. Relatively regular 

4 The comparison between conditions within the surface dyslexia 

group was done using the nonparametric Wilcoxon signed 

ranks test. All these comparisons were also done with the parametric 

Student t-test, with similar results. 

words with potentiophones were read significantly poorer 

than relatively regular words without potentiophones, 

z(16) ¼ 3.5, p ¼ .0005, and irregular words were read significantly 

poorer when they had a potentiophone than when 

they did not, z(15) ¼ 3.06, p ¼ .002. This also held individually 

for 14 of the participants. The older participants made the 

fewest errors on the irregular words without potentiophone, 

possibly because they learned to block or avoid nonlexical 

responses. 5 

The surface dyslexia of 15 of the participants was pure, 

with very few errors that did not result from reading via 

grapheme-to-phoneme conversion, as seen in Table 3. Notice 

that none of the participants produced semantic or morphological 

paralexias, indicating that they were not reading aloud 

via the semantic system. TM and AK had developmental 

attentional dyslexia in addition to developmental surface 

dyslexia, but because the words were presented to them separately, 

a single word at a time, this did not affect their performance 

in the study. AK also had a mild letter position 

dyslexia 6 (Friedmann and Gvion, 2001, 2005; Friedmann and 

5 The regular words with potentiophones were read as poorly as 

the irregular words with potentiophones, and for some of the participants 

even significantly more poorly, as a result of the regularity 

and frequency relations between each target words and its 

potentiophone in the two word groups tested (see Lukov and 

Friedmann, 2006 for the detailed examination of the effect of frequency, 

regularity, and type of irregularity on reading aloud of 

various words). 

6 This was diagnosed using a list of 232 words with lexical potential 

for middle letter migration, in which he made 31 middle 

letter migration errors (13.4%), and a screening test that included 

64 migratable words, in which he made nine middle migrations 

(14%) (both tests from the TILTAN test battery, Friedmann and 

Gvion, 2003).

1152 

cortex 44 (2008) 1146–1160 

Table 3 – Number of other errors in reading the 340 word list 

Participant Morphological 

error 

Semantic 

error 

Transposition 

error 

Neglect 

error 

Visual 

error 

Other 

error 

SH 0 0 0 0 0 0 

GL 0 0 5 0 0 0 

OF 0 0 1 0 5 0 

YR 0 0 4 0 3 0 

TM 0 0 1 5 1 0 

NT 0 0 0 0 1 0 

OM 0 0 0 0 0 0 

BZ 0 0 0 0 0 0 

AS 0 0 2 0 2 0 

OS 0 0 1 0 1 0 

AK 0 0 5 0 0 0 

AM 0 0 1 0 0 0 

AL 0 0 0 0 1 0 

KR 0 0 1 0 0 0 

NF 0 0 0 0 0 0 

IR 0 0 1 0 0 0 

YD 0 0 3 0 0 0 

Rahamim, 2007) so we did not include the words in which he 

made letter migration errors in any analysis. 

2.3.1.1. NONWORD READING. The five participants who read the 

nonword list, TM, OM, BZ, AM, and YD, showed unimpaired 

reading of nonwords. OM and YD made no errors in their nonword 

reading; TM, BZ, and AM had between one and two migration 

errors which they immediately corrected, in the 

nonwords in which a transposition created an existing word. 

The good reading of nonwords indicates that the participants 

tested had intact sublexical route. 

The following sections present the results of the lexical 

decision and comprehension tasks. Table 4 summarizes the 

performance of each of the participants on the three levels – 

reading aloud of irregular words and potentiophones, which 

was presented in this section, and lexical decision and 

Table 4 – Percentage errors in tasks of the three levels: reading aloud of irregular words and potentiophones, lexical 

selection, and homophone/potentiophone comprehension 

Participant Grade group Deficit location Reading aloud Lexicon Semantics 

SH 5 Orthographic lexicon 35 24 41 

GL 5 Orthographic lexicon 38 24 23 

OF 5 Orthographic lexicon 25 11 15 

YR 5 Orthographic lexicon 52 12 27 

TM 5 Orthographic lexicon 49 38 58 

NT 5 Orthographic lexicon 51 63 a 48 

OM Middle Orthographic lexicon 35 12 8 

BZ Adult Orthographic lexicon 23 9 14 

AS 5 Orthographic lexicon output 26 4 36 

OS 5 Orthographic lexicon output 44 4 30 

AK Middle Orthographic lexicon output 22 1 10 

AM 5 Interlexical 33 4 5 

AL 5 Interlexical 20 3 5 

KR 5 Interlexical 24 1 5 

NF Middle Interlexical 33 3 5 

IR Middle Interlexical 14 2 0 

YD Adult Interlexical 12 0 1 

Thresholds for performance significantly different from the control groups 

Fifth graders 10 5 14 

Middle school 5 4 7.5 

Adults 2.7 1 3 

The shaded cells include performance that is significantly poorer than that of the relevant control group. 

a NT received a different task in which he made lexical decisions for single words rather than selection between two options. This score is the 

percentage of pseudohomophone which he accepted as words.

cortex 44 (2008) 1146–1160 1153 

comprehension, which will be presented in the next sections. 

The bottom rows of Table 4 include the threshold for each 

task above which the number of errors of a dyslexic participant 

is significantly larger (Crawford and Howell’s (1998) 

t-test, p < .05) than the age-matched control group. (For example, 

the adults control group had an average of 1.0% errors 

in reading aloud irregular/potentiophonic words, with SD of 

0.9%. For these data, given 16 participants in this control 

group, the lowest score that would be significantly different 

from the control would be 2.7% errors, using Crawford and 

Howell’s (1998) t-test, and this is presented in Table 2.) 

2.3.2. Lexical decision 

The participants differed with respect to their ability to decide 

which of two letter strings was a word spelled correctly, as 

seen in Table 4. Whereas nine of the participants performed 

within the normal range in this task ( p > .05 for the comparison 

of each of them with their controls), eight performed significantly 

poorer than their controls (t > 6, p < .001). 

2.3.3. Homophone and potentiophone comprehension 

The assessment of homophone/potentiophone comprehension 

showed that some of the participants performed well in 

this task, indicating preserved access to semantics, whereas 

others did poorly. As seen in Table 4, six of the participants 

performed within normal limits in the homophone selection 

task, whereas the other participants performed significantly 

poorer than their control groups ( p < .05), five of them 

performing at chance level on this task. Thus, the results 

yielded 3 patterns: impaired reading aloud, lexical decision, 

and comprehension; impaired reading aloud and comprehension, 

with intact lexical decision; and impaired reading 

aloud with intact lexical decision and comprehension. 

2.3.4. Naming 

The results of the naming task are reported in Table 5. The 

naming performance of 16 of the 17 participants was within 

the normal range, with performance ranging between 92 and 

100 items named correctly out of 100 items, indicating intact 

lexical access and retrieval. Especially relevant for surface 

dyslexia, in which some individuals showed impaired phonological 

output lexicon, the naming ability of the participants in 

this study indicates that they had no impairment at the phonological 

output lexicon. None of the participants produced 

a phonemic paraphasia, indicating also an intact phonemic 

output buffer for all the participants. 

One participant, AS, performed below the normal range, 

with 88% correct naming, which might indicate a deficit in 

lexical retrieval as well. Unlike previously reported individuals 

with acquired surface dyslexia, the pattern of his errors 

and other responses in the naming task did not indicate 

a deficit in the phonological output lexicon, which is usually 

manifested in phonologically related paraphasias. His errors 

were close semantic paraphasias, hesitations, and don’t know 

responses, and only one of his paraphasias was a formal 

paraphasia, which was not only phonologically, but also semantically, 

related to the target word. AS’s response pattern 

is not characteristic of a deficit in the phonological lexicon 

itself, because a deficit at this level is expected to also yield 

phonemic paraphasias. According to his error pattern, AS’s 

mild lexical retrieval difficulties stem from a deficit either 

in the semantic lexicon, or in the access from the semantic 

lexicon to the phonological output lexicon – according to 

Butterworth (1989) and Caramazza and Hillis (1990), when 

there is no access to the phonological representation of 

the target word, a word which is semantically related to it, 

whose phonological representation is available, might be 

produced instead. The fact that he had frequency effect on 

naming (r pb ¼ .2, p ¼ .03) further supports a deficit in the access 

to the phonological output lexicon rather than a deficit 

in the semantic lexicon (Jescheniak and Levelt, 1994). It 

might be interesting to note that AS’s reading indicated 

that he also had a deficit in the access from the orthographic 

input lexicon to the phonological output lexicon, so his deficit 

might be a general difficulty accessing the phonological 

output lexicon. (This is unlike the other eight individuals 

Table 5 – Performance on naming 100 objects 

Participant Correct responses Don’t know Paraphasia Correct naming following 

Semantic Formal a Long hesitation Semantic paraphasia 

SH 93 1 1 3 2 

GL 96 1 1 1 1 

OF 95 3 2 

YR 92 4 1 3 

OM 96 4 

BZ 100 

AS 88 2 5 1 3 1 

OS 96 2 2 

AK 95 1 2 2 0 

AM 97 3 

AL b 96 1 1 1 1 

KR 92 5 2 1 

NF 99 1 

IR 100 

YD 96 4 

a All the formal paraphasias produced by our participants were phonologically and semantically related to the target. 

b AL’s don’t know response and his correct response following hesitation also included a definition of the target.

1154 

cortex 44 (2008) 1146–1160 

in the current study who had a deficit in the connection of 

the orthographic input lexicon to the phonological output 

lexicon, whose access to the phonological output lexicon 

from semantics was unimpaired.) 

2.3.5. Input surface dyslexia: a deficit at the lexicon or in the 

access to it? 

In the Introduction ascribed the deficit of individuals with 

impaired reading aloud, lexical decision, and comprehension 

to an impairment in the orthographic input lexicon or in the 

access to it. In order to decide which of these two possibilities 

apply for our participants, we further tested the ability of one 

of the participants with this reading pattern, BZ, to perform 

a lexical decision task for both written and orally spelled sequences. 

If it is only the access from the orthographic–visual 

analysis system to the orthographic input lexicon that is impaired, 

whereas the orthographic input lexicon is intact, we 

would expect failure in lexical decision for written words but 

success in the orally spelled words because orally spelled 

words access the orthographic input lexicon from another 

route and not through the visual analyzer. However, if the lexicon 

itself is impaired, both modalities should yield impaired 

performance. 7 

The written lexical decision task administered to BZ included 

108 sequences, 54 words and 54 pseudohomophones. 

The orally spelled lexical decision comprised 34 

words, including 17 existing words and 17 pseudohomophones. 

The results showed that BZ performed poorly on 

both tasks. He accepted 65% and 33% of the pseudohomophones 

as existing words in the oral and written task respectively, 

and rejected 18% and 4% of the existing words, 

respectively. This suggests that BZ’s orthographic input lexicon 

was impaired. 

Another factor that might speak to a deficit in the orthographic 

input lexicon rather than impaired access to it, is 

the effect of frequency. We expect that the orthographic input 

lexicon would be affected by frequency, with higher 

probability of retrieving frequent written words, whereas 

a pre-lexical impairment of access to the orthographic input 

lexicon should not be affected by lexical factors such 

as frequency. For this reason we analyzed the effect of frequency 

on the reading aloud of all participants with input 

surface dyslexia. This was done in two ways: First, we estimated 

the written frequency of the irregular words in the 

340 word list using Google search, and compared the accuracy 

in reading the 20 most frequent irregular words to the 

reading of the 20 irregular words with the lowest frequency 

on the list. For each of the individuals, an effect of frequency 

was found with higher accuracy in reading the 

more frequent words. The second way in which we 

assessed frequency effect was via examination of the relative 

frequency of a target word and its potentiophone. We 

asked 50 individuals without reading disorder to evaluate 

the relative frequency of the 160 target words with potentiophones 

from the 340 words list, compared to their 

7 It is, of course, possible that both access routes to the lexicon 

are impaired, in which case no differential diagnosis can be made 

between impaired lexicon and impaired access to the lexicon 

from all access routes. 

potentiophones. We then selected the 89 potentiophone 

pairs which yielded a significant preference for one of the 

potentiophones. 8 The analysis of reading accuracy showed 

that each of the participants made more errors on the 37 

target words which were less frequent than their potentiophones, 

compared to the number of errors on the 52 target 

words which were more frequent than their potentiophones. 

These two analyses, which point to the effect of 

frequency on reading aloud of each of the individuals 

with input surface dyslexia, indicate a deficit in the lexicon 

rather than the access to it. 

2.3.6. Summary – subtypes and functional localization 

of the deficits 

The results reported above indicate that the participants 

can be classified into three groups, each with a different 

subtype of developmental surface dyslexia. The first group, 

which includes SH, GL, OF, YR, TM, NT, OM, and BZ, 

showed impaired reading aloud, impaired lexical decision, 

and impaired homophone and potentiophone comprehension. 

We suggest that the participants in this group have 

an impairment that relates to the orthographic input lexicon, 

most probably in the lexicon itself. The individuals in 

the second group, AS, OS, and AK, had impaired reading 

aloud, impaired homophone/potentiophone comprehension, 

and good lexical decision. This pattern suggests a functioning 

and accessible orthographic input lexicon, with impaired 

output from it to semantics and to the 

phonological output lexicon. The third group, which included 

AM, AL, KR, NF, IR, and YD, showed impaired oral 

reading of irregular words and potentiophones, but at the 

same time had normal performance in lexical decision 

and in homophone/potentiophone comprehension. This 

pattern can be ascribed to intact orthographic input lexicon, 

which also has intact access to the semantic system, but 

impaired access to the phonological output lexicon. Importantly, 

there were no participants with good homophone 

comprehension who showed impaired lexical decision. 

The naming assessment suggests that the marked tendency 

to read via grapheme-to-phoneme conversion does 

not result from a deficit at the phonological lexicon, at least 

for 16 of the 17 participants, who did not have lexical retrieval 

deficits or phonemic paraphasias. 

3. Discussion 

The main finding of the current study is the identification 

of three subtypes of developmental surface dyslexia. These 

subtypes differ with respect to the locus on the lexical 

reading route that is impaired, all leading to reading via 

the sublexical route, but with different performance pattern 

with respect to orthographic–lexical knowledge and 

comprehension. 

8 We counted a potentiophone as significantly more frequent 

than its counterpart when the number of judges who chose it 

as the more frequent was larger than twice the number of judges 

who chose the counterpart plus the number of judges who said 

they were equi-frequent.

cortex 44 (2008) 1146–1160 1155 

The first subtype of developmental surface dyslexia, input 

surface dyslexia, was a deficit that related to the orthographic 

input lexicon. As a result, the eight individuals who had this 

type of developmental surface dyslexia were forced to read 

via the grapheme-to-phoneme conversion route, and therefore 

made regularization and potentiophone errors in reading. 

Because the orthographic input lexicon was inaccessible to 

them, they also failed on lexical decision, and given that the 

orthographic input lexicon was inaccessible, they could not 

reach the semantic system from reading, and hence made errors 

in comprehension of homophones and potentiophones. 

Frequency effects on reading aloud indicate that the deficit 

of the participants in this group was in the orthographic input 

lexicon rather than in the access to it. For one of the participants 

in this group, this conclusion was supported by his 

poor performance also when the words were spelled aloud 

to him. 9 

The second subtype of developmental surface dyslexia 

that was witnessed in the current study, orthographic lexicon 

output surface dyslexia, was characterized by unimpaired 

orthographic input lexicon, but impaired connection from 

it to the next stages: phonological output lexicon and the 

semantic system. As a result, the three individuals who 

had this surface dyslexia subtype read aloud via the sublexical 

route, and hence made regularization and potentiophone 

errors, but still could identify the correct spelling 

of written words, and choose between the correct spelling 

of a word and its pseudohomophone. However, because 

the access from the orthographic input lexicon to the semantic 

system was impaired, they could not use their intact 

lexical knowledge to access the correct meaning of 

homophones and potentiophones, and had to access meaning 

in an indirect way: they read the words via the sublexical 

route, and the input to semantics was the phonological 

result of this conversion. This led to failure in the homophone/potentiophone 

comprehension task. 

The third subtype of developmental surface dyslexia 

identified in this study, interlexical surface dyslexia, resulted 

from disconnection between the orthographic input lexicon 

and the phonological output lexicon. Because of this disconnection, 

the six individuals with this subtype of developmental 

surface dyslexia had to read via the sublexical 

route, which caused regularization and potentiophone errors 

in reading aloud, but when they did not have to reach 

the phonological output lexicon, in tasks of lexical decision 

and comprehension, they performed at a normal level. That 

is to say, because they had access to the orthographic input 

lexicon, they could identify the correct spelling of written 

words, and because they had access from the orthographic 

input lexicon to the semantic system, they could also access 

the meaning of lexical items from the orthographic input 

lexicon, and therefore their comprehension was intact 

9 When discussing developmental surface dyslexia, it is hard to 

imagine how an intact orthographic input lexicon would develop 

when the access to it from visual analysis is impaired. Thus, it is 

unlikely to find such a deficit in developmental surface dyslexia, 

of impaired access to the orthographic input lexicon, but with intact 

orthographic input lexicon. Such a deficit might be more 

clearly manifested in acquired dyslexia. 

even for homophones and potentiophones. Their impairment 

was in the connection between the orthographic 

and the phonological lexicons rather than in the phonological 

output lexicon itself, as indicated by their good naming 

performance. 

One other pathway could theoretically be employed by the 

participants with the interlexical disconnection – because the 

semantic system is accessible to them, they could have proceeded 

to oral reading via the pathway from semantics to the 

phonological output lexicon. However, the finding that none 

of these participants made even a single semantic or morphological 

paralexia indicates that they did not use this route 

for oral reading. A possible conclusion is that the route for 

reading aloud via the semantic system is only employed as 

a last resort, when neither the direct route nor the sublexical 

route is available for reading. This is the case in deep dyslexia, 

where this is the only route available, and reading via 

it yields many semantic and morphological errors. 

The fact that this distinction was found in developmental 

dyslexia suggests that the orthographic input lexicon 

can develop even when its output is impaired, and that developmental 

dyslexias can exhibit selectivity in impairment, 

similar to acquired dyslexias. It is interesting to note that 

the selective impairment of the participants reported in 

the current study is even more selective than that reported 

for adults with acquired surface dyslexia. First, whereas for 

some participants with acquired surface dyslexia the sublexical 

route was not completely intact (Coltheart, 2006), 

the five participants in the current study who were tested 

in nonword reading read them well, indicating a good sublexical 

route. 

Furthermore, apart from surface dyslexia that results 

from a deficit at the orthographic input lexicon, the two subtypes 

that were reported in the literature included either 

a deficit to the phonological output lexicon or a semantic 

deficit (Ellis et al., 2000). Whereas the individuals reported 

in studies of acquired surface dyslexia (Bub et al., 1985; Graham 

et al., 1994; Howard and Franklin, 1987; Kay and Ellis, 

1987; Kay and Patterson, 1985; McCarthy and Warrington, 

1986; Patterson and Hodges, 1992; Shallice et al., 1983) had 

general lexical or semantic–conceptual deficits, not only in 

reading, the participants in the current study had no aphasia, 

and only one of them had mild naming difficulties. 

This leads to an important difference between the subtypes 

of surface dyslexia described in the literature until now, and 

the subtypes we describe in the current study. In the current 

study two new subtypes were found, which involved the 

connections between components rather than a deficit to 

the components themselves. 10 One subtype results from 

a deficit in the connections between the orthographic input 

lexicon and both the semantic system and the phonological 

10 We do not think that the fact that subtypes of acquired surface 

dyslexia reported until now involved damage to the lexicon or the 

semantic system whereas the subtypes in the current study of 

developmental surface dyslexia did not involve lexical and semantic 

impairment, relates to some deep difference between acquired 

and developmental dyslexia. There is no reason to assume 

that the two types of surface dyslexia we described here that result 

from damage to the connections from the orthographic input 

lexicon cannot occur in acquired surface dyslexia as well.

1156 

cortex 44 (2008) 1146–1160 

output lexicon, the other subtype involves a deficit in the 

connection between the orthographic input lexicon and the 

phonological output lexicon. The phonological output lexicon 

was not impaired, and nor was the semantic system. 

Thus the results confirm the existence of two new subtypes 

of surface dyslexia, which were predicted theoretically from 

the dual route reading model, but have not been attested 

until now. 

The identification of subtypes of developmental surface 

dyslexia suggests an interesting angle to look at two related 

debates concerning developmental dyslexia: whether the underpinnings 

of developmental dyslexia are phonological, and 

whether developmental dyslexia can be described in terms 

of selective deficits to a reading model similar to that 

suggested for skilled adult readers, and hence with types similar 

to those identified in acquired dyslexia. In order to answer 

the first question, consider what individuals with developmental 

surface dyslexia of all three types can do, i.e., what is 

the skill that they use all the time for reading aloud. What 

they do is analyze the input letter sequence, segment it, 

convert graphemes to phonemes, and then combine the 

phonological segments and produce an integrated phonological 

representation. In other words, children with developmental 

surface dyslexia are very proficient exactly in phonological 

skills, and their deficit resides elsewhere, in the lexical route. 

As Marshall (1998) put it, ‘‘These children manifest reading 

difficulties . precisely because they have acquired the core 

skills that Shaywitz claims are impaired in developmental 

dyslexia’’. This finding emphasizes that developmental dyslexia 

is not generally a phonological deficit, and that claims 

about phonological bases for developmental dyslexia should 

be made scrupulously, and with reference to specific subtypes. 

The general claim that developmental dyslexia results 

from a phonological deficit or from poor phonemic awareness 

(Frith, 1997; Goswami, 2002; CM Marshall et al., 2001; Snowling, 

1998; Stanovich, 1988) might be true for some types of developmental 

dyslexia (specifically, phonological and deep 

dyslexia), but is not applicable to other subtypes. Developmental 

dyslexias do not necessarily come with poor phonemic 

awareness and not all of them result from poor phonemic 

awareness (Castles and Coltheart, 2004; Friedmann and Rahamim, 

2007) or a phonological deficit (see McCloskey and Rapp, 

2000 for a discussion). Some studies that directly tested phonemic 

awareness in children with developmental surface dyslexia 

actually found that these children performed above 

average in meta-phonological tests (Lukov and Friedmann, 

2004; Valdois et al., 2003). Thus, whereas phonological deficits 

and deficits in the phonological–sublexical route might cause 

considerable difficulties in reading, not all reading difficulties 

result from phonological deficits. 

Relatedly, the current research indicated that pure surface 

dyslexia exists in a developmental form, and that subtypes 

can even be identified within it, subtypes which can 

be readily accounted for within the framework of the dual 

route model for reading. The characteristics of reading 

aloud in developmental surface dyslexia that emerge from 

the current study are remarkably similar to the pattern of 

reading in acquired surface dyslexia described in the literature 

(Patterson et al., 1985) and for acquired surface dyslexia 

in Hebrew (Gvion and Friedmann, 2001). These 

results thus join a growing body of studies that provide robust 

evidence for the existence of subtypes of developmental 

dyslexia, which show striking similarity to subtypes of 

acquired dyslexia. This has been reported for developmental 

surface dyslexia (Broom and Doctor, 1995a; Castles 

et al., 2006; Castles and Coltheart, 1993, 1996; Coltheart 

et al., 1983; Judica et al., 2002; Masterson, 2000; Temple, 

1997; Valdois et al., 2003), developmental phonological dyslexia 

(Broom and Doctor, 1995b; Howard and Best, 1996; 

Temple, 1997; Temple and Marshall, 1983; Valdois et al., 

2003), developmental direct dyslexia (Glosser et al., 1997), 

developmental deep dyslexia (Stuart and Howard, 1995; Siegel, 

1985; Temple, 1988, 2003), as well as for developmental 

peripheral dyslexias: developmental letter position dyslexia 

(Friedmann and Rahamim, 2007), developmental attentional 

dyslexia (Rayner et al., 1989), and developmental neglect 

dyslexia (neglexia, Friedmann and Nachman-Katz, 2004; 

Nachman-Katz and Friedmann, 2007). (For a comprehensive 

survey of this literature see Brundson et al., 2002; Castles 

et al., 2006; Castles and Coltheart, 1993; Castles et al., 

1999; Temple, 1997.) 

Such wealth and diversity of subtypes of developmental 

dyslexia cannot be accounted for by a single deficit underlying 

developmental dyslexia, but it can be clearly interpreted 

using the dual route model of reading, as resulting from deficits 

to various components of the model, similar to subtypes 

of acquired dyslexia (Castles et al., 2006; Castles and 

Coltheart, 1993; Coltheart et al., 1983; Marshall, 1984b; 

Temple, 1997). 

Another result of this study is the way surface dyslexia 

manifests itself in a highly irregular language, Hebrew. The 

discussion of surface dyslexia in English, for example, focuses 

on irregular words that include a grapheme with 

two possible conversions to phoneme, which occurs in its 

less frequent conversion, or words with silent letters (such 

as sword, island, receipt, buffet, sew, listen). In Hebrew, many 

such words exist, because nine of the 22 letters have ambiguous 

conversion to phonemes. However, ambiguous letters 

are not the only source of ambiguity in grapheme-to-phoneme 

conversion. The underspecification of vowels in the 

orthography, and the lack of marking for stress position (in 

the absence of default stress), create an orthography in 

which no word is regular – namely, there is no written 

word that can be unambiguously converted to phonemes. 

The findings of the current study indicated that in such orthography 

not only do ambiguous letters get the incorrect 

conversion to phonemes, but, also, incorrect vowel pattern 

and stress position are chosen for the whole word in the absence 

of vowel and stress specifications, sometimes resulting 

in a nonword and sometimes in another existing word. 

Another important factor for reading in surface dyslexia, at 

least in Hebrew, is the potentiophonic status of the target 

word. When the letter sequence can be read via grapheme-to-phoneme 

conversion as another existing word, 

such errors occur even when the word is relatively regular. 

For example, and can both be converted to /k/, and the 

letter can be converted to /v/, /u/, and /o/. Thus, the word 

(KMOT, wake-up-plural, /kamot/), although relatively 

regular, when read via the sublexical route, can be read as 

the word (QMOT, quantity, /kamut/). The special

cortex 44 (2008) 1146–1160 1157 

susceptibility of potentiophones to reading errors results 

from the fact that when a reader reads a potentiophone 

via the sublexical route incorrectly, she cannot know that 

she has made an error because the result is another existing 

word (for the effect of frequency and regularity on potentiophone 

errors see Lukov and Friedmann, 2006). Potentiophones 

are especially helpful in the detection of surface 

dyslexia, because errors cannot be detected and corrected 

by the reader, and because, unlike homophones, even reading 

aloud can already indicate a deficit in reading via the 

lexical route. Homophones, on the other hand require additional 

comprehension tasks. 

The identification of subtypes of developmental surface 

dyslexia is interesting and important not only for its theoretical 

implications. It also has immediate implications for 

diagnosis and treatment. With respect to diagnosis of developmental 

surface dyslexia, the current results suggest that it is 

not enough to detect that an individual reads via the sublexical 

route by assessing her performance in reading aloud. 

Tasks involving lexical decision and homophone/potentiophone 

comprehension are required to discover the exact locus 

of impairment in the reading process. 

The distinction between different loci that can cause reading 

via grapheme-to-phoneme conversion can also be used to 

discern developmental surface dyslexia from impoverished 

orthographic lexicon that results from limited exposure to 

reading. In many cases children with other types of dyslexia, 

such as peripheral dyslexias, avoid reading as much as they 

can (see Cunningham and Stanovich, 1998; Share, 1999; Stanovich, 

1986; Stanovich and West, 1989), and as a result do 

not establish a rich orthographic input lexicon. This, in 

turn, results in ‘‘surface-dyslexia-like’’ reading (Friedmann 

and Gvion, 2002; Friedmann and Nachman-Katz, 2004; Friedmann 

and Rahamim, 2007; Nachman-Katz and Friedmann, 

2007; Rahamim and Friedmann, in press). The administration 

of lexical decision and homophone comprehension tasks in 

addition to oral reading can help in determining whether 

the child has surface dyslexia or whether it is just an impoverished 

orthographic input lexicon secondary to another dyslexia. 

If the deficit is found to be located at the orthographic 

input lexicon, other ways will be needed to make the decision, 

but if the deficit is found to be located elsewhere, in 

the output of the orthographic input lexicon to the phonological 

output lexicon or to semantics, this will suggest that it is 

indeed a genuine surface dyslexia, and not a phenomenon 

secondary to reading avoidance. 

With respect to treatment, different treatment plans 

should be applied to the different subtypes of surface dyslexia 

– treatment for individuals with a deficit at the orthographic 

input lexicon should include improving the 

operation of this lexicon (see Coltheart and Byng, 1989; 

Weekes and Coltheart, 1996), and establishing robust lexical 

entries in this lexicon by means of mnemonics and repeated 

exposure for example. However, if the orthographic input 

lexicon is intact and functioning, the treatment should be directed 

elsewhere. For example, the work with individuals 

who have access to the orthographic input lexicon but cannot 

access the phonological output lexicon and semantics should 

be directed at improving these connections, and for individuals 

who have surface dysgraphia alongside this type of 

surface dyslexia, reading for monitoring of writing can be 

trained. For those individuals who read aloud incorrectly 

via the sublexical route but who understand words correctly 

via the route from the orthographic input lexicon to the semantic 

system, the advice should be – do not read aloud. 

To summarize, developmental surface dyslexia has several 

faces. The current study identified three groups of individuals 

who had different subtypes of developmental surface dyslexia. 

All subtypes resulted from an impaired lexical route, 

which forced reading via grapheme-to-phoneme conversion, 

causing difficulties in reading irregular words and potentiophones, 

but they differed with respect to the locus of impairment 

within the lexical route, and, as a result, in the 

manifestation of the deficit in lexical decision and 

comprehension. 

Acknowledgements 

This article is dedicated to the memory of John Marshall, 

who led the way in the classification of dyslexias, was the 

first to describe surface dyslexia in detail, and deeply believed 

that developmental dyslexias can and should be classified 

similarly to acquired dyslexias. Shalom, John. We 

thank Dror Dotan, Ivana Nachman-Katz, Julia Reznick, 

Maya Yachini, Michal Biran, Terri Sternberg, and Uri Hadar 

for their helpful comments on the paper. This research 

was supported by the Israel Science Foundation (grant no. 

1296/06, Friedmann). 

Appendix A 

Ambiguous grapheme–phoneme and 

phoneme–grapheme correspondences 

in Hebrew 

Ambi-phoneme letters in Hebrew 

Hebrew letter Phonemes Transcript 

ae(ø oi)’(glottal stop) 

A 

vb 

B 

aeø’ 

H 

vuo 

O 

iy(a eei) 

I 

kx 

Q 

’ aea ? 

pf 

P 

ssh 

S 

Ambi-letter phonemes in Hebrew 

Phoneme Letters Transcript 

a 

’(glottal stop) 

v 

x 

t 

k 

s 

H?A 

H?A 

OB 

XQ 

Tt 

KQ 

Ss

1158 

cortex 44 (2008) 1146–1160 

Appendix B 

Examples for errors the participants made in reading aloud 

Target 

word 

Target 

letters 

Target 

pronunciation 

Target 

translation 

Response 

pronunciation 

Response 

translation 

Potentiophone 

response 

spelling 

Comments 

Potentiophone 

error 

Regularization 

error 

Ambiguous 

letter error 

QTR keter crown katar locomotive 

KOB? kove’a determines kova hat 

QIsA kise chair kisa covered 

BRIQH brexa pool brixa run-away 

LMROT lamrot although limrot to-pluck 

QTF katef shoulder kataf picked 

BL?DIO Bil’adav without-him baladiyo – 

MROX maruax spread marux – 

RAS rosh head ra’ash noise Potentiophone 

KISOA kishu zucchini kiso’a – 

SMLH simla dress shimla – can be read 

as sh or s (sh is 

the more frequent 

conversion) 

ASMX esmax I-will-be-happy ashmax – can be read 

as sh or s 

CINOR cinor pipe cinur – can be read as 

o,u,or v 

HTLBtH hitlabta pondered hitlavata – can be read as 

borv 

Vowel error TXBR texaber she-will-connect taxbar – Error in 

unrepresented 

vowel 

LNKOT lenakot to-clean lankut – Error in 

unrepresented 

vowels and 

ambiguous vowel 

letter 

SRtTM saratetem you-pl-scratched sertatem Error in 

unrepresented 

vowels 

TB?t tiv’at You-will-kick taba’at ring Potentiophone þ 

ambiguous 

letter þ error in 

unrepresented 

vowels 

PRsIT parsit Farsi persit – Error in 

unrepresented 

vowels 

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Developmental surface dyslexias - Naama Friedmann

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