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ORIGINAL RESEARCH
published: 05 November 2019
doi: 10.3389/fpsyg.2019.02401
Edited by:
Fan Cao,
Sun Yat-sen University, China
Reviewed by:
Claudio Mulatti,
University of Padova, Italy
Alexandra Isabel Dias Reis,
University of Algarve, Portugal
*Correspondence:
Naama Friedmann
naamafr@tauex.tau.ac.il
Specialty section:
This article was submitted to
Language Sciences,
a section of the journal
Frontiers in Psychology
Received: 04 May 2019
Accepted: 08 October 2019
Published: 05 November 2019
Citation:
Güven S and Friedmann N (2019)
Developmental Letter Position
Dyslexia in Turkish, a Morphologically
Rich and Orthographically Transparent
Language. Front. Psychol. 10:2401.
doi: 10.3389/fpsyg.2019.02401
Developmental Letter Position
Dyslexia in Turkish, a
Morphologically Rich and
Orthographically Transparent
Language
Selçuk Güven1,2 and Naama Friedmann3*
1School of Communication Sciences and Disorders, McGill University, Montreal, QC, Canada, 2Department of Speech
and Language Therapy, Anadolu University, Eski ¸sehir, Turkey, 3Language and Brain Lab, Sagol School of Neuroscience and
School of Education, Tel Aviv University, Tel Aviv, Israel
We present the first report of a specific type of developmental dyslexia in Turkish,
letter position dyslexia (LPD). LPD affects the encoding of letter positions, leading
to letter migrations within words. In a multiple case study of 24 Turkish-speaking
children with developmental LPD, we examined in detail the characteristics of this
dyslexia and explored its manifestation in Turkish. We used migratable words, in which
a migration creates another existing word (e.g., signer-singer), which exposed the
migration errors of the participants. In sharp contrast with the common assumption
that dyslexics in transparent languages, including Turkish, do not make reading errors,
we have shown that right stimuli can detect even up to 30% reading errors. The
participants made migrations in reading aloud, comprehension, lexical decision, and
same-different tasks, in both words and non-words. This indicates that their deficit
is in the orthographic-visual analysis stage, a stage that precedes the orthographic
input lexicon and is shared by the lexical and non-lexical routes. Their repetition of
non-words and migratable words was normal, indicating that their phonological output
stages are intact. They did not make digit migrations in reading numbers, indicating
that the orthographic-visual analyzer deficit is orthographic-specific. The properties of
Turkish allowed us to examine two issues that bear on the cognitive model of reading:
consonant-consonant transpositions were far more frequent than consonant-vowel and
vowel-vowel migrations. This indicates that the orthographic-visual analyzer already
classifies letters into consonants and vowels, before or together with letter position
encoding. Furthermore, Turkish is very rich morphologically, which has allowed us to
examine the effect of the morphological structure of the target word on migrations. We
found that there was no morphological effect on migrations: morphologically complex
words did not yield more (nor fewer) migrations than monomorphemic ones, migrations
crossed morpheme boundaries and did not preserve the morphological structure of
the target word. This suggests that morphological analysis follows the letter-position
encoding stage.
Keywords: developmental dyslexia, letter position dyslexia, Turkish, transparent orthography, morphology
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Güven and Friedmann Letter Position Dyslexia in Turkish
INTRODUCTION
Dyslexia is a general term relating to a deficit in reading. By
now, more than 20 different types of dyslexia have been reported,
each with different error types and different characteristics,
each resulting from impairments in different stages of the
word reading process (Marshall, 1984;Castles and Coltheart,
1993;Ellis and Young, 1996;Jackson and Coltheart, 2001;
Castles, 2006;Coltheart and Kohnen, 2012;Castles et al., 2014;
Friedmann and Haddad-Hanna, 2014;Hanley, 2017;Friedmann
and Coltheart, 2018). Even though much work has been done
about types of dyslexia in various languages, almost no studies
have examined the way different types of dyslexia manifest
themselves in Turkish. In fact, only one paper reported a
specific type of dyslexia in Turkish, and it was a study of
acquired dyslexia (Raman and Weekes, 2005); we could not
find any study that described specific types of developmental
dyslexia in Turkish.
In this study, we describe, for the first time, a specific type of
developmental dyslexia in Turkish and its characteristics.
We report on a multiple case study of 24 Turkish-
speaking children who show a developmental dyslexia that
affects their ability to encode the position of letters: letter
position dyslexia (LPD).
According to the dual-route model (Coltheart, 1981, 1985,
1987;Patterson, 1981;Ellis et al., 1987;Shallice, 1988;Humphreys
et al., 1990;Coltheart et al., 1993, 2001;Ellis and Young,
1996), the early stage of word reading includes the visual
analysis of the letter string. It encodes the abstract identity
of the letters and their relative positions (Coltheart, 1981;
Humphreys et al., 1990;Ellis and Young, 1996). Letter position
dyslexia is a deficit in the function that encodes the relative
positions of letters within words, which leads to letter migrations
within words (e.g., slime →smile, cloud →could). Studies
in several languages found that LPD is mainly manifested
in migratable words, i.e., words in which letter migration
creates other existing words (such as flies and files,slept and
spelt). Most of the migration errors affect the middle letters,
whereas the first and the last letters are relatively immune
to migrations. Errors in migratable words are affected by
frequency so that more errors occur when the target word
(spelt) is less frequent than its migration counterpart (slept)
(Friedmann and Rahamim, 2007). Individuals with LPD were
found to make significantly more migrations that involve
only consonants than migrations of a vowel and a consonant
(Khentov-Kraus and Friedmann, 2018).
Letter position dyslexia has been reported so far for Hebrew,
Arabic, and English (Friedmann and Gvion, 2001, 2005;
Friedmann and Rahamim, 2007, 2014;Friedmann et al., 2010;
Friedmann and Haddad-Hanna, 2012, 2014;Kohnen et al.,
2012), in both acquired form (Friedmann and Gvion, 2001,
2005, for Hebrew; and Friedmann and Haddad-Hanna, 2012
for Arabic) and developmental form (Friedmann and Gvion,
2005;Friedmann and Rahamim, 2007;Friedmann et al., 2010 for
Hebrew; Friedmann and Haddad-Hanna, 2012, 2014, for Arabic;
Kohnen et al., 2012 for English). Until now, LPD has not been
reported for Turkish.
A Brief Description of the Characteristics
of the Turkish Language and
Orthography
Turkish is morphologically very rich, and a single Turkish
word may include multiple suffixes (e.g., the word
“güldüremediklerimizdensin,” which means “you are the one
that we were unable to make laugh,” contains eight suffixes).
The modern orthography of Turkish is composed of a 29-letter
alphabet of eight vowels and 21 consonants, based on a modified
Latin script. In most cases, a single phoneme is represented with a
single grapheme, and the grapheme-to-phoneme correspondence
is consistent and transparent (Raman, 1999). The only exceptions
are words borrowed from other languages, which are usually
transferred into Turkish with their original phonology. For
example, the word “katip,” which is borrowed from Arabic, is
written with a single abut read, like in the Arabic origin, with
a long a,/kaatip/. Syllables in Turkish (except for loan words)
comprise of a single vowel. Canonical syllable structure in
Turkish is CV, but other structures (such as V, VC, and CVC)
also exist. Syllables with consonant clusters are rare (Raman,
1999), and the length of the vowel restricts the consonants of the
coda (Kabak and Vogel, 2001). Stress position is regular and final
(with some exceptions, Kabak and Vogel, 2001).
Dyslexia in Turkish
Very few studies about Turkish took the neuropsychological
approach to acquired and developmental dyslexia. Or, in Raman
and Weekes (2008) more positive words, “Research addressing
the cognitive neuropsychology of acquired language disorders
in Turkish has only just begun to flourish.” The exception is
a study by Raman and Weekes (2005) who studied in detail a
Turkish-English bilingual stroke patient who had an acquired
lexical-phonological retrieval deficit, which made him unable
to read via the lexical route. This led to surface dyslexia in
English, and imageability effects in reading Turkish, with good
reading of non-words.
We could not find any study on types of developmental
dyslexia in Turkish. The few papers that examined developmental
dyslexia in Turkish did not make the distinctions between
different types of developmental dyslexia and have not
characterized the types of errors each of the individuals
with developmental dyslexia made. Raman (2011) tested a group
of students with developmental dyslexia (without identifying the
type of dyslexia each of them had) and examined the effect of
Age of Acquisition in word and picture naming in this group
in comparison to a non-dyslexic control group. Other studies
worked under the assumption that dyslexia in Turkish mainly
affects reading fluency (Erden et al., 2002;Özmen, 2005;Ergül,
2012). Studies of reading in typical development focus mainly on
the contribution of phonological abilities to reading and spelling
acquisition both in monolingual (Öney and Durguno˘
glu, 1997;
Durguno˘
glu, 2002;Kesikçi and Amado, 2005;Babayi˘
git and
Stainthorp, 2010) and bilingual populations (Özdemir et al.,
2012;Özata et al., 2016).
The current study, therefore, aims to start filling the gap
by (1) reporting and exploring in detail a type of dyslexia
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Güven and Friedmann Letter Position Dyslexia in Turkish
that has not been reported for Turkish yet, in either the
acquired or developmental form. Exploring its characteristic
error types and the properties of stimuli that are more susceptible
to errors. (2) Reporting for the first time a specific type of
developmental dyslexia in Turkish. (3) Examining the common
belief that Turkish readers with dyslexia do not make reading
errors – we will demonstrate that, when the relevant stimuli are
selected, they definitely do make errors. The rich morphology
and the CV structure of Turkish would further allow us to
ask questions about properties of LPD that have not been
tested so far: (4) What is the relative order of morphological
decomposition and letter position encoding. (5) How early
in the reading process are letters encoded as consonants
or vowel letters.
MATERIALS AND METHODS
Participants
Dyslexic Group
The dyslexic participants in this study were 24 monolingual
Turkish-speaking children in 4th grade, aged 9–10, 8 males
and 16 females. All of them were right-handed. All of
the participants were living in Eski¸sehir, Turkey. They were
pupils in regular schools and regular classes. According to
the reports of their parents and/or teachers, and through
informal observation made by SLPs, none of them had
speech and language disorders (beyond reading deficits),
nor any history of brain lesion, neurological condition, or
cognitive problems. None of them had been previously
diagnosed as having dyslexia or learning disability. However,
when we discussed their reading with their teachers, the
teachers expressed concerns about the reading of almost all
the participants.
To select individuals who have developmental LPD for this
study, we administered the dyslexia screening task FR˙
IGÜ
(Güven and Friedmann, 2014), described in the next section.
We included individuals in the LPD group according to the
following inclusion criteria: significantly higher total number
of errors in the screening test compared with the age-matched
group, significantly more letter position errors in the screening
test than the control group (and at least 6 letter position errors),
and less than 10% for other types of errors.
The 24 children with LPD were identified in the following way:
16 children were identified in a school-wide reading testing in
which we administered the FR˙
IGÜ reading screening test to 299
children. The other 8 children were recruited from teachers in
6 schools (in which children from varying SES – low-middle-
high– status). The teachers referred children to us who they
suspected had learning or reading difficulties. We tested the
reading of these children using the FR˙
IGÜ screening test, 8 had
LPD and fitted the inclusion and exclusion criteria so they were
included in the study.
Control Groups
The control group for the screening task included 205 fourth
graders, 111 girls and 94 boys, with no report of reading disability.
The control group for the further LPD tests included 71 fourth
graders aged 9 to 10 years, 39 males and 32 females who had no
speech, language, hearing or other cognitive problems, based on
teacher or parent reports. Additionally, the children who were
examined for the control group were tested by speech-language
pathologists, who reported their clinical opinion regarding each
child’s language. We excluded three children who the testers
suspected to have a language disorder.1
Procedure
Each of the participants was tested individually in a quiet room
in the school. All stimuli were displayed on a white page in 14
pt. font, with double vertical spacing between words. No time
limit was imposed during testing, the written word lists remained
in front of the participants for as long as they needed, and no
response-contingent feedback was given by the experimenter.
In the silent reading tasks, we instructed the participant not to
read aloud. In orally presented tests, the experimenter repeated
every item as many times as the participant requested. Each of
the participants took part in 13 tests, which were administered
in several sessions. The number of sessions and length of each
session were determined by each of the participants. The research
was approved by the Ethical Committee of Anadolu University,
Eski¸sehir, Turkey. The parents of each child signed written
informed consent.
General Error Coding and Analysis
In the analysis of letter transpositions, we classified the
transpositions according to the letters that participated in
the transposition: consonant-consonant, vowel-consonant, and
vowel-vowel migrations. If the participant produced a sequence
of responses to a target word, and one of these responses was an
error, we counted the item as being incorrect and analyzed the
erroneous response.
Statistical Analyses
We examined whether each participant with dyslexia performed
significantly below his or her age-matched control group
using one-tailed Crawford and Howell’s (1998) t-test. Within-
participant comparisons between two conditions were conducted
using chi-squared tests (two-tailed comparisons). At the group
level, comparisons between two conditions were conducted using
the Wilcoxon Signed-Rank test, which is the non-parametric
counterpart of paired samples t-test (reported with z statistic),
and more than two conditions were compared using Friedman
Test. For the correlation, Spearman’s rank correlation coefficient
analysis was used. Effect sizes for t-tests are reported with Hedges’
g, and for Wilcoxon’s, when there is no normal distribution, with
r(Fritz et al., 2012). Comparisons at the group level between the
LPD group and the large control group were done using the t-test.
An alpha level of 0.05 was used in all comparisons.
1The age-matched control group was in fact also a reading-age matched group
for many of the LPD participants: if we define a reading age control group by the
total rate of errors in the non-migratable words in the screening test, the 205 age-
matched control participants made an average of 1.1 errors (SD = 0.9), and 13 of
the LPD participants performed within the normal range for their age on these
words.
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Güven and Friedmann Letter Position Dyslexia in Turkish
THE SCREENING TEST USED TO
IDENTIFY CHILDREN WITH LPD FOR
THIS STUDY
The first test we administered, which we used for initial
assessment and identification of individuals with LPD to include
in the study, and to examine the properties of their errors, was
the screening test from the FR˙
IGÜ test battery (Güven and
Friedmann, 2014), which was developed to identify types of
dyslexia in Turkish. The screening part of the FR˙
IGÜ is an oral
reading test that includes three blocks: 151 single words (2–8
letters long, M= 5.12, SD = 1.29), 60 word pairs (4–5 letters
long, M= 4.88, SD = 0.92), and 40 non-words (2–9 letters long,
M= 5.16, SD = 1.62). The word reading block was used to identify
individuals with LPD according to the criteria described above.
Some researchers have claimed that in certain languages (e.g.,
languages with transparent orthographies), dyslexia does not
manifest itself in errors, only in slow reading. We think this
is a misconception that partly results from not using the right
stimuli to elicit reading errors. Our approach was, on the basis
of the approach of the Tiltan reading battery (Friedmann and
Gvion, 2003), to base the reading test on knowledge of the types
of words and non-words that are most sensitive to each type
of dyslexia, i.e., the type of stimuli in which individuals with
this kind of dyslexia make most errors of the relevant type. Ever
since the early days of the cognitive neuropsychological approach
to dyslexia – Marshall and Newcombe (1973); Coltheart (1981),
and Patterson (1981) found that dyslexias differ with respect to
the types of stimuli that are most difficult in them. So there are
“dimensions of words” as Patterson called it, for example, surface
dyslexia is most evident in reading irregular words, phonological
dyslexia in non-words, and deep dyslexia in abstract words,
function words, and morphologically complex words.
The word and non-word lists of the FR˙
IGÜ screening test
were thus constructed so that they include items that are
sensitive to each of the currently known types of dyslexia; words
with different stress patterns or with ambiguous grapheme-
to-phoneme conversion for identifying surface dyslexia;
function words and morphologically complex words to identify
phonological output buffer dyslexia, orthographic input buffer
dyslexia, and deep dyslexia; abstract words for deep dyslexia;
words (and non-words) with many orthographic neighbors
for identifying orthographic analyser-output visual dyslexia,
orthographic input buffer dyslexia, and letter identity dyslexia;
words (and non-words) that can be read as other words by
neglecting one side of the word, for identifying neglect dyslexia;
and words in which vowel letter omissions, additions, migrations,
or substitutions create other existing words, for the identification
of vowel letter dyslexia.
The non-words were included for identifying phonological
and deep dyslexia as well as various peripheral dyslexias;
the word pairs were constructed such that between-word
migrations create other existing words, to enable the detection
of attentional dyslexia.
Importantly, the screening part of FR˙
IGÜ was designed to
also detect LPD. The list of 151 words contains 121 migratable
words: 91 words in which a middle letter migration would create
another existing word, and 54 words in which migration of
exterior letters creates a word (24 of these words allowed for both
interior and exterior migrations).
Results: Reading Screening Test
The participants with LPD made between 6 and 19 letter position
errors in the single word reading block, with an average of
10.3 letter position errors (SD = 4.1). The control participants,
on the other hand, made only 1.8 letter position errors on the
average in this task (0–5 errors, SD = 2). Each of the LPD
children performed significantly poorer than the control group
[t(204) >1.94, p<0.02, for each of the participants].
ORAL READING OF MIGRATABLE AND
NON-MIGRATABLE WORDS
Now that the screening task identified 24 children who had
LPD, we continued with a line of tests that were developed
to examine the nature of this dyslexia, and the way it is
manifested in Turkish. We created a list of 183 migratable
words to allow for the in-depth assessment of the effect of
morphology on migrations (see section “Does Morphological
Analysis Precede Letter Position Encoding? Assessing the
Interaction of Morphology and Migrations”); the effect of
the consonant-vowel status on migration (see section “Is
Letter Position Encoding Sensitive to the Consonant-Vowel
Status of the Target Letters?”); the position of the migrating
letters within the word (assessing middle-exterior, adjacent-non-
adjacent, within-across syllable, and length effect, see section
“Further Analyses of the Properties of Letter Migrations in
Turkish”); and frequency effect (see section “What Is the Nature
of the Letter Position Encoding Deficit? Incorrect Underspecified
Encoding? The Effect of Frequency on Migrations and Its
Theoretical Implication”).
Experimental Stimuli
The migratable word list included 183 migratable words, 4-to-8
letters long (M= 5.2, SD = 0.9). Each of these words was such that
at least one letter migration within the word results in an existing
word (see examples for various types of migrations in Table 1).
Each of the words in the list was also such that a letter identity
error could create another existing word.
Results
Migrations in Reading Migratable Words
The LPD participants made a total of 433 migration errors in
reading the migratable word list. Figure 1 summarizes the letter
position error rates the children with LPD made. Each of the
24 children with LPD made significantly more migrations than
the control group (p<0.001, using Crawford and Howell’s,
1998,t-test for the comparison of an individual to a control
group). The difference was also significant at the group level,
where the LPD group made significantly more letter migrations
(10% migrations) than the control group (who made only 1%
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Güven and Friedmann Letter Position Dyslexia in Turkish
TABLE 1 | Examples for migration errors of various types that the LPD participants made.
Condition Target word Response with
migration error
Translation word Translation response Example from English
Middle migrations
Adjacent consonant-consonant (CC)
migration
altı atlı six horseman badly-baldy
Adjacent consonant-vowel (CV) migration alınma alnıma to take offense to my forehead from-form
Consonant-consonant migration across a
vowel (C-C)
ebedi edebi eternal literary slime-smile
Vowel-vowel migration across a consonant
(V-V)
çelik çilek steel strawberry toner-tenor
Exterior migrationsa
Adjacent consonant-vowel (CV) migration atkı takı scarf jewel acres-cares
Consonant-consonant migration across a
vowel (C-C)
yakın yanık close burn inlet-intel
Vowel-vowel (Exterior) migration across a
consonant (V-V)
katı kıta stiff continent demo-dome
aThere were no words with a potential of exterior adjacent CC migrations, due to the Turkish syllable structure.
0%
2%
4%
6%
8%
10%
12%
14%
16%
18%
20%
T.E.K. F.A. M.L. A. B.A. C.G. S.U. D.Ç. U.S. S.Y. M.K. M.C. S.S. M.B. B.K. E.K. D.Ö. B.Y. Z.E.K. E.A. Z.E.S. S.A. İ.Ç. G.E.
Control Group % Migraons of Each LPD Parcipant
M = 1.15%, 95% CI [0.8-1.2]
FIGURE 1 | Reading migratable words: % letter position errors of each LPD participant (orange circles) compared to the control group average (horizontal blue line)
in reading the list of 183 migratable words.
migrations on this list, SD = 1.27), t(24) = 10.71, p<0.0001, with
a very large effect size (g= 2.53). See Table 1 for examples for the
various types of migrations that the participants with LPD made.
Refuting a Misconception: Turkish Dyslexics Do
Make Errors When the Appropriate Stimuli Are
Presented: Migratable vs. Non-migratable Words
We asked whether the participants make more migration errors
when the target words are migratable, i.e., words in which a
migration error can create another existing word (like the English
word form, in which a migration error can create from) than on
non-migratable words.
We compared the migrations in the list of 183 migratable
words to the rate of migrations in reading a list of non-migratable
words, which included words in which no single transposition
created an existing word (e.g., the target word gözlük [glasses],
for which all possible migrations result in non-lexical responses).
This non-migratable word list included 32 words, 4-to-7 letters
long (M= 4.9, SD = 0.7), with a relatively high frequency (all
were among the 5000 most frequent words in Turkish, and more
than half of them were among the top 2000 most frequent words,
according to Aksan et al. (2016) frequency data.
This analysis showed a striking difference between migratable
and non-migratable words: the children with LPD made
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Güven and Friedmann Letter Position Dyslexia in Turkish
TABLE 2 | % migration errors in migratable and non-migratable words.
Participant Migratable words
(N= 183)
Non-migratable words
(N= 32)
T.E.K. 12 0
F.A. 14 0
M.L. 19 0
A.C. 11 0
B.A. 7 0
C.G. 10 0
S.U. 4 0
D.Ç. 4 0
U.S. 5 0
S.Y. 13 0
M.K. 12 0
M.C. 8 0
S.S. 15 0
M.B. 9 0
B.K. 11 0
E.K. 9 0
D.Ö. 7 0
B.Y. 10 0
Z.E.K. 12 0
E.A. 5 0
Z.E.S. 7 0
S.A. 5 0
˙
I.Ç. 18 0
G.E. 9 0
Average (SD) 10 (4) 0
N = number of words that allow for at least one error of the relevant type.
no migrations in non-migratable words, whereas they made
an average of 10% migrations in reading the migratable
words (Table 2).
Relatedly, to examine whether the letter position errors of
the participants with LPD tended to create existing words,
we analyzed their migration responses in reading migratable
words. For each migratable word, there was at least one option
for a migration that yields an existing word, and at least one
other option for migration response that yields a non-word.
We examined whether the participants’ migrations tended to
create existing words.
This analysis showed that when they read a migratable word
with a migration error, most of their responses were lexical
(76.6% of their migration responses were lexical, SD = 31.2%).
The same was true in reading migratable non-words, in which,
as we report below in Section “What Is the Locus of LPD in the
Reading Model: Nonword Reading and Silent Reading Tasks –
Results”, most errors were lexical as well.
The tendency to produce lexical responses guided us in the
analyses of the characteristics of the participants’ migrations:
for each analysis, we calculated the rate of errors out of the
number of target words in which such errors would create
an existing word, i.e., words that have a lexical potential for
the relevant error type (for example, we calculated adjacent
migrations not out of all words, but rather only out of the
target words in which a migration of adjacent letters creates
an existing word).
DOES MORPHOLOGICAL ANALYSIS
PRECEDE LETTER POSITION
ENCODING? ASSESSING THE
INTERACTION OF MORPHOLOGY AND
MIGRATIONS
Turkish has a very rich morphology, so studying LPD in Turkish
readers allowed us to examine a theoretical question about the
interaction between letter position encoding and morphological
analysis. Specifically, we were interested in the relative order
in which letter position encoding and morphological analysis
take place. If morphological analysis precedes letter position
encoding, then the morphological structure of the target
word should affect letter position errors, and migrations
should occur only within a morpheme. If, however, letter
position encoding precedes morphological analysis, then the
morphological structure of the target word should not affect
migration errors.
To examine this question, we used three kinds of analysis.
We examined whether morphologically complex words
yielded a different rate of letter position errors than mono-
morphemic words. We also tested whether letter migrations
changed the morphological structure of the target word and
whether migrations occurred only within morpheme or also
across morphemes.
Analyses and Results
The first analysis examined whether morphologically complex
words yield a different rate of letter position errors than
morphologically simple words. For this analysis, we compared
44 morphologically-complex words from the migratable word
list (which includes words with derivational and words with
inflectional morphemes) to 78 monomorphemic migratable
words. We selected these words so that they would be matched on
length, which led us to include 4–6 letters long morphologically
complex words (M= 5.39, SD = 0.61) and 5–7 letters long
monomorphemic words (M= 5.22, SD = 0.47), so the word
lengths in the two groups did not differ significantly.
The results were such that the children with LPD had
very similar rates of migrations on the morphologically
complex words (8.9%) and on the morphologically simple
words (9.5%), and this difference was not significant
(Wilcoxon z = 0.24, p= 0.81).
In the second analysis, we examined whether the migrations
changed the morphological structure of the target word. This
analysis indicated that there were quite a few migrations that
changed the morphological structure of the target word: 21%
of the migrations changed the morphological structure of the
target word (SD = 19%). For example, the monomorphemic
target word akran (peer) was read with a transposition as
“arkan”, a morphologically complex word, constructed from
arka (back), and the suffix –n (singular 2nd person possessor).
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Or the morphologically simple target word eskiz (sketch), which
was read with a transposition as the morphologically complex
“eksiz” in which the stem ek means “supplement” (or, to confuse
us, “a morpheme”), and the suffix siz means “without” (so
this morphologically complex word actually means “without a
morpheme” i.e., a monomorphemic word).
The final analysis tested whether migrations occurred only
within-morpheme or also across morphemes. This analysis
indicated that, in reading the morphologically complex words,
the participants transposed letters of the stem with letters
of the non-stem morpheme (e.g., konulu: konu-lu, themed
→kolunu: kolu-nu, your arm). Such cross-morpheme migrations
occurred on 6.3% of the morphologically complex words
(SD = 3.7). In fact, migrations within the stem, which involved
two letters of the stem (yenile: yeni-le, renew →yinele: yine-
le, repeat) and migrations within the non-stem morpheme
(kirli: kir-li, dirty →kiril, Cyrillic) occurred less frequently
than across-morpheme migrations (within the stem: 2% of the
morphologically complex words, SD = 2.3, within the non-stem
morpheme: 0.7%, SD = 1.1).
These three kinds of evidence for the lack of sensitivity of
letter position errors to the morphological structure of the target
word suggest that LPD affects a stage that precedes morphological
analysis, and hence, it is not sensitive to the morphological
structure of the target words.
IS LETTER POSITION ENCODING
SENSITIVE TO THE
CONSONANT-VOWEL STATUS OF THE
TARGET LETTERS?
To examine the theoretical question of when the consonant-
vowel distinction becomes accessible during the process of single
word reading, we examined the effect of the consonant-vowel
status of a letter on the rate of migrations.
We asked two main questions: whether consonant and
vowel letters are differentially susceptible to migrations,
and whether they tend to migrate more within their class
(consonants transpose with consonants and vowels with vowels)
than across class.
Analyses
For this sake, we compared four types of migration:
(1) V1CV2: a transposition of two vowels across a consonant
[e.g., eli (his/her hand) >“ile” (with)]
(2) C1VC2: a transposition of two consonants across a vowel
[e.g., tak (attach) >“kat” (floor)]
(3) CC: a transposition of two adjacent consonants: [e.g., atlı
(horseman) >“altı” (six)]
(4) CV: a transposition of adjacent consonant and vowel [e.g.,
atlı (horseman) >“atıl” (idle)]
We did this analysis only for the participants who did not
have vowel dyslexia (Khentov-Kraus and Friedmann, 2018) in
addition to LPD, because a higher rate of migrations that involve
vowels may, in their case, be a result of their vowel dyslexia.
Within the 183 migratable words list, there were 98 words in
which a consonant-consonant migration creates another word
(51 words allowing for Adjacent CC migrations and 67 allowing
for CC migration across a vowel); 63 words that allow for adjacent
consonant-vowel migration, and 74 words that allow for a vowel-
vowel transposition across a consonant.
Results
The results, summarized in Table 3, indicated a clear difference
between the different kinds of migration. Migrations that
involved only consonants (either adjacent CC transposition or
CVC- transposition of two consonants across a vowel) were
the most common type of migration (14%), whereas migrations
that involved only vowel letters, or migrations that involved
a consonant and a vowel occurred less often (5% each).
TABLE 3 | Consonant and vowel letter migrations of the participants with LPD in
migratable word reading (% migrations of each type out of the number of
migratable words with a lexical potential for such error).
Participant All C-C
(N= 98)
C-C across
V (N= 67)
V-V across
C (N= 74)
Adjacent
CC (N= 51)
Adjacent
CV (N= 63)
F.A. 23 16 3 18 6
M.L. 30 18 1 22 17
A.C. 20 13 0 16 5
B.A. 8 4 5 6 5
C.G. 19 13 0 18 2
S.U. 7 4 1 6 2
D.Ç. 5 3 0 4 5
U.S. 8 6 3 8 0
S.Y. 13 10 3 10 14
M.K. 21 22 1 10 2
M.C. 12 12 4 8 0
M.B. 12 6 1 14 8
B.K. 16 10 3 18 3
E.K. 11 6 4 12 5
D.Ö. 6 3 0 4 14
B.Y. 13 6 5 18 3
Z.E.K. 16 12 4 16 5
E.A. 7 3 1 8 3
Z.E.S. 11 3 1 16 2
S.A. 6 3 1 12 3
˙
I.Ç. 26 28 0 12 13
G.E. 9 9 9 6 0
Average (SD) 14(7) 10(7) 2 (2) 12(5) 5(5)
Participants with LPD and vowel dyslexia
S.S. 9 4 12 12 14
T.E.K. 11 7 12 2 11
C = consonant letter, V = vowel letter, N = number of words in which at least one
error of the relevant type creates an existing word (some words allow for more than
one type of error: e.g., the target word “istem” can be read with adjacent CC error
as itsem, or with a C-C error across V as ismet. So it is counted once as a word
with any C-C migration potential, and once in words with adjacent CC migrations
potential, and also once in words with CC across V migrations potential). Due to the
syllable structure in Turkish, we had no words with adjacent VV migration potential
and no non-adjacent CV.
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A Friedman’s test indicated that the difference between the
three types of migration (C with C, C with V, and V with V)
was significant, χ2(2) = 30.45, p<0.001, with consonant-only
migrations being the most frequent migrations.
Consonants migrated across vowels (C1V C2→C2V C1)
significantly more frequently than vowels across a consonant
(V1C V2→V2C V1), Wilcoxon z = 4.42, p<0.0001,
r= 0.64. Consonants transposed with an adjacent consonant
(CC) significantly more often than with adjacent vowels (CV),
Wilcoxon z = 3.85, p<0.0001, r= 0.56.
Another type of analysis that points in exactly the same
direction is the analysis of the “preferred migration type” in target
words that allow for several types of migrations (C-C, V-V, V-C).
There were 64 such target words, and the participants showed
the same tendency toward consonant migrations: when they read
a word in which several types of migrations were possible, they
most often made a C-C migration (67% of the migrations on
these words) and had much fewer V-V migrations (17%) or
C-V migrations (16%). The C-C migrations were significantly
more frequent than the other migration types, Friedman’s test
χ2= 21.62, p<0.001.
The results show clearly that consonant letters are more
susceptible to transpositions than vowel letters, and that
consonant-only transpositions occur more frequently than
transpositions that involve a consonant and a vowel letter.
Beyond its bearing on the characterization of LPD, this finding
that indicates that the classification of letters to consonants and
vowels happens very early in the process of orthographic-visual
analysis, before or together with letter position encoding, and
that consonant letters are processed separately and differently
from vowel letters.2It is also interesting to note that the two
children who had vowel dyslexia in addition to letter position
dyslexia (SS and TEK, presented in the bottom of Table 3) made
more transpositions that involve a vowel than transpositions that
include only consonants.
FURTHER ANALYSES OF THE
PROPERTIES OF LETTER MIGRATIONS
IN TURKISH
Middle vs. Exterior Letter Migrations
Studies of LPD in Hebrew, Arabic, and English report that
individuals with LPD make more migrations that involved only
middle letters than migrations that involve an exterior letter
(Friedmann and Gvion, 2001;Friedmann and Rahamim, 2007;
Friedmann and Haddad-Hanna, 2012, 2014;Kohnen et al., 2012).
2The difference between consonant-only migrations and migrations that involved
a vowel letter is not due to frequency differences between the conditions,
which were evenly distributed between the relative-frequency conditions. Within
each frequency condition – similar frequency between target and migration
counterpart, target more frequent than migration, migration result more frequent
than target – the LPD participants made far more migrations that involved only
consonant letters than migrations that involved vowel letters (CV and VV) 25%
CC and 9% CV/VV in the frequent migration counterpart condition, 13% CC and
6% CV/VV in the similar frequency condition, and 12% CC and 3% CV/VV in the
frequent target word condition.
To examine whether this was also the case for Turkish LPD,
we compared the rates of migrations that involved only middle
letters and migrations that also involved an exterior (first
or final) letter.
The 183 migratable words list included 91 words that have
at least one possibility for middle migration, 34 words with a
possibility for a migration that involves an exterior letter, and 58
words with a potential for both middle and exterior migrations.
The results, presented in Table 4, show that the Turkish-
readers with LPD made both middle letter migrations and
exterior letter migrations, but they, like LPD participants in the
other languages tested, made significantly more migrations of
middle letters (9%) than migrations that involved an exterior
letter (6%), Wilcoxon z = 2.73, p= 0.006, r= 0.39.
This predominance of middle migrations can also be seen in
another type of analysis that assesses the “preferred migration
type” in target words in which both middle and exterior
migrations create other existing words. There were 55 such target
words, and the participants showed the same tendency toward
middle migrations: when they read a word in which both a
middle migration and an exterior migration would create existing
words, they made almost three times more middle migrations
(73%) than exterior ones (27%), a difference that was significant,
Wilcoxon z = 5.06 p<0.0001.
Migrations of Adjacent and
Non-adjacent Letters
Hebrew readers with LPD make more migrations in adjacent
letters than non-adjacent letters. We tested whether this is the
case also for Turkish children with LPD.
Within the 183 migratable words list, in 61 words only
adjacent letter migrations created other existing words, 95 words
allowed only for non-adjacent letter migration, and 27 words
had a lexical potential for both adjacent and non-adjacent
letter migration.
The results, summarized in Table 4, show that the Turkish
LPD participants made significantly more migrations in adjacent
letters (12%) than in non-adjacent letters (7%), Wilcoxon z = 3.09,
p= 0.002, r= 0.45. However, as we report in Section “Is
Letter Position Encoding Sensitive to the Consonant-Vowel
Status of the Target Letters?,” the consonant-vowel status of the
letter affects migration considerably; once the consonant-vowel
status is kept constant (analyzing only consonant-consonant
migrations), the size of the difference between adjacent and
non-adjacent letters shrinks, Wilcoxon z = 2.02, p= 0.04.
Migrations Across and Within Syllables
We also investigated whether more migrations occur within-
or across syllables. The results, presented in Table 4, show
that there were significantly more across-syllable migrations
(8%) than within-syllable migrations (5%), Wilcoxon z = 3.07,
p= 0.002, r= 0.44.
Length Effect
To examine the effect of word length on the rate of migrations,
we analyzed the participants’ migration rates in reading aloud
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TABLE 4 | Percentages migrations of the various kinds that the participants with LPD made in reading migratable words.
Participant Total (N= 183) Adjacent
(N= 86)
Non-adjacent
(N= 120)
Middle
(N= 149)
Exterior
(N= 90)
Across syllable
(N= 153)
Within syllable
(N= 94)
T.E.K. 12 10 11 10 8 10 6
F.A. 14 16 10 13 7 14 4
M.L. 19 23 13 15 13 17 10
A.C 11 13 8 10 6 11 3
B.A. 7 7 6 6 4 6 4
C.G. 10 10 8 9 6 9 5
S.U. 4 5 3 5 1 4 2
D.Ç. 4 5 3 2 4 3 3
U.S. 5 5 5 5 2 5 3
S.Y. 13 16 8 11 7 11 6
M.K. 12 7 13 7 12 11 5
M.C. 8 5 9 9 2 8 3
S.S. 15 17 10 12 10 10 12
M.B. 9 14 4 7 7 7 6
B.K. 11 13 8 10 6 8 7
E.K. 9 10 6 9 3 7 6
D.Ö. 7 13 2 4 8 4 7
B.Y. 10 14 6 11 2 10 4
Z.E.K. 12 14 8 13 2 10 6
E.A. 5 7 3 4 3 3 4
Z.E.S. 7 12 2 7 1 7 2
S.A. 5 7 3 5 1 5 2
˙
I.Ç. 18 17 15 13 16 10 19
G.E. 9 16 2 9 3 9 2
Average (SD) 10 (4) 12 (5) 7 (4) 9 (3) 6 (4) 8 (4) 5 (4)
N = number of words that allow for at least one error of the relevant type.
TABLE 5 | The relationship between the number of letters and LPD error rate.
Word Length Number of words % migrations
4 letters 31 10
5 letters 101 9
6 letters 33 8
7 lettersa18 19
aThis group included 17 7-letter words and a single 8-letter word.
the list of 183 4–8 letter migratable words (see section
“Experimental Stimuli”).
We conducted Spearman’s Rho correlation coefficient analysis
to see if there is a relationship between length and migration
errors. A correlation analysis of the results (presented in Table 5)
indicated that the correlation coefficient was low and non-
significant (R=−0.11, p= 0.19).
WHAT IS THE LOCUS OF LPD IN THE
READING MODEL: NON-WORD
READING AND SILENT READING TASKS
The next question was where in the word-reading model is the
impairment that gives rise to LPD. For this sake, we examine
the participants’ non-word reading and compare it to their
word reading (section “Non-word Reading” below): if they
make migration errors in non-words as well, this would mean
that the deficit is not in lexical components and that it is
rather in a component that is shared by lexical and non-lexical
processes. We then test the participants’ silent reading using
various tasks to examine whether the locus is in the orthographic-
visual analysis stage. If it is, a deficit in the orthographic-visual
analysis should cause migrations not only in reading aloud but
also in lexical decision and comprehension of written words
(section “Silent Reading Tasks” below). If the deficit is indeed
in the orthographic input, phonological output should not show
migrations when the input does not involve reading. This we
tested in Section “Assessing Phonological Output Using Non-
word and Word Repetition,” which examined the participants’
phonological output using non-word and word repetition.
Non-word Reading
To examine how the LPD participants read non-words, and to
further test whether their deficit was pre-lexical or at a lexical
stage, we presented them with an additional list of 60 non-words.
The non-words in the list were 4-to-6 letters long (M= 4.92,
SD = 0.42). Half of the non-words (30) were migratable, i.e.,
non-words in which a letter migration creates an existing word
(e.g., the non-word “bakrı” is migratable because the migration
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of the two middle consonants creates the word “barkı,” his/her
home). The other 30 non-words were non-migratable so that no
migration created another word (e.g., “solik” or “bike¸s”).
The 30 migratable non-words were selected to allow the
examination of the characteristics of migrations also in non-
words. To compare middle and exterior letter migrations, 27
of the non-words were such that at least one migration of an
exterior letter would create an existing word, and 10 non-words
were such that migration of middle letters would create an
existing word (7 of these words had both middle and exterior
migration potential). There were 15 words that had a potential of
consonant-consonant transposition, 3 words with a potential of
vowel-vowel transposition, and 25 words with vowel-consonant
transposition potential.
Results
The 24 participants with LPD made an average of 18% migrations
when reading the migratable non-words. The rate is significantly
higher than that of the control group (2%), t(25) = 7.63,
p<0.0001, g= 1.8. On the individual level (see Figure 2), 21
children with LPD made significantly more migration errors than
the control group (14 children p<0.001, and 7 children p<0.05,
using Crawford and Howell’s (1998),t-test).
The participants made significantly more migrations in
reading the migratable non-words (18%) than in reading the
non-migratable non-words, where they made 7% migrations
(Wilcoxon z = 4.41, p= 0.0001, r= 0.64). Still, the rate of
migrations that the children with LPD made in non-migratable
non-words was significantly larger than that of the control group,
who only made 0.3% migrations in non-migratable non-words,
t(23) = 4.92, p<0.0001, g= 1.16. This finding is important
because it indicates that the deficit that underlies the migration
errors in LPD is not in the orthographic input lexicon but
rather in an earlier stage that affects words, non-words, and
non-migratable non-words: the orthographic-visual analyzer.
When we analyzed the errors that the LPD participants
made in reading the migratable non-words (presented in detail
in Table 6), we see that, like in their reading of the existing
migratable words, they made significantly more migrations in
middle letters (31%) than migrations that involved an exterior
letter (9%; Wilcoxon z = 4.51, p= 0.0001, r= 0.65). They made
significantly more migrations that involved only consonants
(22%) than migrations of a consonant and a vowel (11%),
Wilcoxon z = 3.01, p= 0.001, r= 0.44, and significantly more
migrations across syllables (24%) than within a syllable (9%),
Wilcoxon z = 4.30, p= 0.0001, r= 0.62.
Like in the word reading, most of the error responses the
LPD participants made in reading the migratable non-words
were lexical (M= 81.3% of the total errors in migratable non-
words, SD = 17.1%), with significantly more lexical errors than
non-lexical errors, Wilcoxon z = 5.36, p<0.001, r= 0.77.
When we only look at migration responses in reading the
migratable non-word list, the picture remains the same: most
of their migration responses were lexical (M= 88.6% of their
transposition errors in migratable non-words, SD = 44.3%;
significantly more lexical than non-lexical migration responses,
Wilcoxon z = 5.63, p<0.001, r= 0.82).
Not surprisingly, when they made migration errors in reading
non-migratable non-words, where migrations could not yield
an existing word, they produced mainly non-lexical responses
(M= 33.6% of the total errors in non-migratable non-words,
SD = 35.1%, Wilcoxon z = 2.87, p= 0.002, r= 0.42).
Silent Reading Tasks
If the source of letter migrations is indeed in a deficit in the
orthographic-visual analysis stage, we would expect migrations
0%
5%
10%
15%
20%
25%
30%
35%
40%
45%
50%
T.E.K. F.A. M.L. A. B.A. C.G. S.U. D.Ç. U.S. S.Y. M.K. M.C. S.S. M.B. B.K. E.K. D.Ö. B.Y. Z.E.K. E.A. Z.E.S. S.A. İ.Ç. G.E.
Control Group % Migraons of Each LPD Parcipant
M = 2%, 95% CI [1.5-2.5]
FIGURE 2 | Migratable non-word reading: % letter position errors of each LPD participant orange circles) compared to the control group (horizontal blue line).
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TABLE 6 | Characteristics of migration errors in reading migratable non-words (% errors in each of the stimulus types).
Participant Total
(N= 30)
Middle
(N= 10)
Exterior
(N= 27)
Across syllable
(N= 14)
Within syllable
(N= 25)
C-C (N= 15) V-V (N= 3) C-V (25) Adj. CC
(N= 13)
Adj. CV
(N= 19)
T.E.K. 17 10 15 7 16 13 0 16 8 16
F.A. 13 30 4 21 4 20 0 4 23 5
M.L. 47 50 33 36 36 33 0 44 31 47
A.C. 30 60 11 57 4 40 33 12 46 11
B.A. 7 10 4 14 0 7 33 4 8 0
C.G. 17 50 0 36 0 33 0 0 38 0
S.U. 7 20 0 14 0 13 0 0 15 0
D.Ç. 17 50 0 36 0 33 0 0 38 0
U.S. 17 30 7 29 4 13 33 12 15 11
S.Y. 20 30 11 21 12 27 0 12 23 11
M.K. 13 30 4 21 4 27 0 4 23 0
M.C. 10 10 7 14 4 13 33 8 8 0
S.S. 23 40 7 29 12 27 0 16 23 16
M.B. 17 30 7 21 8 27 0 8 31 0
B.K. 30 50 15 43 12 33 67 20 31 11
E.K. 17 40 4 21 8 20 0 8 31 5
D.Ö. 37 30 30 29 28 20 33 32 31 32
B.Y. 13 10 11 7 12 7 0 12 8 16
Z.E.K. 17 10 15 7 16 7 0 16 8 21
E.A. 13 40 0 29 0 27 0 0 31 0
Z.E.S. 3 10 0 7 0 7 0 0 8 0
S.A. 13 20 7 21 4 13 33 8 15 5
˙
I.Ç. 33 50 19 43 16 47 0 20 38 11
G.E. 13 30 4 21 4 27 0 4 23 0
Average (SD) 18 (10) 31 (16) 9 (9) 24 (13) 9 (9) 22 (11) 11 (19) 11 (11) 23 (12) 9 (12)
C = consonant letter, V = vowel letter, N = number of words that allow for at least one error of the relevant type, Adj. = Adjacent.
to occur in silent reading tasks that do not involve reading
aloud. To examine this, we ran 3 reading tasks that did not
involve reading aloud: lexical decision, same-different decision,
and comprehension.
Lexical Decision
The word list for lexical decision included 59 items: 29 words and
30 non-words, 4–5 letters long (M= 4.89, SD = 0.37). All the
words and non-words were migratable. We asked the participants
to read the list silently and mark only the existing words.
Results
The participants with LPD made an average of 19% (SD = 12.9%)
errors on the lexical decision task, significantly more than the
control group (8%, SD = 5.4%), t(25) = 4.06, p= 0.0004, g= 0.96.
The participants made 20% errors of accepting migratable non-
words as existing words, and 18% errors of judging existing
words as non-words. The individual performance of the LPD
participants is presented in Figure 3. In the individual level
analysis, 16 of the 24 LPD participants performed significantly
poorer than the control group (p<0.05).
Same-Different Decision
In the same-different task, the participants were presented with
60 written pairs of 4–7 letter words (M= 5.08 letters, SD = 0.67),
presented side by side with a single space between them. Half of
the pairs (30 pairs) included two migratable words that differed
in the position of the middle letters. The other 30 pairs included
identical migratable words. We asked the participants to decide,
for each pair, whether the two words were the same or different.
Results
The participants with LPD made significantly more errors in
this task (9%) than the control group (who made 2% errors),
t(23) = 2.83, p= 0.009, g= 0.67. The LPD participants made
9% errors in which they said “same” for pairs of words that
differed in the order of letters, and 10% errors in which they said
“different” for identical pairs of migratable words. The analysis
of the individual performance of the LPD participants, presented
in Figure 4, showed that 12 of the 24 participants performed
significantly poorer than the control group (p<0.05).
Comprehension Task: Migratable Word Association
We assessed the comprehension of migratable words using a
word association task. The task included 28 items. Each item
included 4 words: a target migratable word and 3 words from
which the participant needed to select one. The target migratable
word allowed for at least two different migrations that can create
existing words. The three options included one word that is
semantically related to the target word (e.g., for the target word
eksi, minus, the semantically related word was negatif, negative).
The two distractor words were semantically related to possible
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0%
10%
20%
30%
40%
50%
60%
70%
T.E.K. F.A. M.L. A. B.A. C.G. S.U. D.Ç. U.S. S.Y. M.K. M.C. S.S. M.B. B.K. E.K. D.Ö. B.Y. Z.E.K. E.A. Z.E.S. S.A. İ.Ç. G.E.
% Migraons of Each LPD Parcipant Control Group Average
FIGURE 3 | Lexical decision: % letter position errors of each LPD participant (orange columns) compared to the control group average (blue horizontal line).
0%
10%
20%
30%
40%
50%
60%
70%
T.E.K. F.A. M.L. A. B.A. C.G. S.U. D.Ç. U.S. S.Y. M.K. M.C. S.S. M.B. B.K. E.K. D.Ö. B.Y. Z.E.K. E.A. Z.E.S. S.A. İ.Ç. G.E.
% Migraons of Each LPD Parcipant Control Group Average
FIGURE 4 | Same-different task: % letter position errors of each LPD participant (orange columns) compared to the control group average (blue horizontal line).
migration counterparts of the target word. For example, “eksi”
can be read with migration as “eski” (old) and as “kesi” (cut), so
for the first migration, we have presented the word “yeni” (new),
and for the second migration “bıçak” (knife). We selected target
words according to the characteristics that we knew induced
more migrations in our participants’ reading: most of the target
words had a potential for middle CC migration, and the target
words were less frequent than their migration result, which were
semantically related to the distractors. We tried as much as
possible to use non-migratable words for the three options (88%
of the options were non-migratable).
The target word was presented in orange on the left, and the
three options were presented in black, one above the other to its
right, in random order. We requested the participants to select
the word that was most related to the target word.
Results
The children with LPD made 33% errors in this task, an error
rate that was significantly higher than that of the control group
(which was only 5%), t(24) = 9.61, p<0.0001, g= 2.27. Each of
the LPD participants made significantly more errors in this task
than the control group (for 20 LPD children, p<0.001; for the
rest 4 children, p<0.05), see Figure 5 for the performance of
each participant.
Assessing Phonological Output Using
Non-word and Word Repetition
In order to further explore the locus of impairment that
gives rise to LPD and to examine an alternative explanation
according to which the migration errors resulted from a deficit
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Güven and Friedmann Letter Position Dyslexia in Turkish
0%
10%
20%
30%
40%
50%
60%
70%
T.E.K. F.A. M.L. A. B.A. C.G. S.U. D.Ç. U.S. S.Y. M.K. M.C. S.S. M.B. B.K. E.K. D.Ö. B. Y. Z.E.K. E.A. Z.E.S. S.A. İ.Ç. G.E.
% Migraons of Each LPD Parcipant Control Group Average
FIGURE 5 | Comprehension task: % letter position errors of each LPD participant (orange columns) compared to the control group average (blue horizontal line).
in the phonological output buffer, we assessed these children’s
phonological output using a non-word repetition task and a
task of repeating words that the participant had read with a
migration error.
Non-word Repetition
The participants repeated non-words using a standardized non-
word repetition task (Turkish Non-word Repetition Test, Topba¸s
et al., 2014). The test included 30 items (1–5 syllables long),
which consisted of 15 non-words that violate Turkish phonotactic
constraints, 10 non-words that obey Turkish phonotactic rules,
and 5 morphologically complex non-words. The test is normed
with 150 typically developing children.
Results
All of the 16 LPD children who participated in the non-word
repetition task performed this task within the normal range, with
scores above the threshold for impaired repetition. The mean
number of correct repetition of the LPD participants was 27.7
(out of 30), SD = 1.47.
Migratable Word Repetition
For each of the 19 children who participated in this task,
we selected 10 of the migratable words that they read with a
migration error and we then asked them to repeat these words.
Results
All of the 19 LPD children who participated in the migratable
word repetition task performed this task flawlessly, with no
migration error, and in fact, with no other error too.
The results of the two repetition tasks indicate that the
participants had no phonological output buffer deficit, and
support our conclusion, reached on the basis of the silent reading
tasks, that the origin of the deficit that underlies LPD is in the
input reading stages.
Theoretical Conclusion: LPD Is a Deficit
in the Letter Position Encoding Function
in the Orthographic-Visual Analysis
Stage
The results of the three silent reading tasks: same-different
decision, lexical decision, and written word comprehension
(summarized in Figure 6) all point to the same conclusion: LPD
affects not only reading aloud but also tasks that involve reading
without oral production. These results, together with the findings
that LPD affected both words and non-words, point to the locus
of impairment in the reading model as a deficit that affects the
early pre-lexical stage of orthographic-visual analysis rather than
the phonological output stages. This conclusion is supported
by the normal phonological output abilities the participants
demonstrated in non-word and migratable words repetition.
WHAT IS THE NATURE OF THE LETTER
POSITION ENCODING DEFICIT?
INCORRECT OR UNDERSPECIFIED
ENCODING? THE EFFECT OF
FREQUENCY ON MIGRATIONS AND ITS
THEORETICAL IMPLICATION
Examining the effect of the relative frequency of the target word
and its migration counterpart can shed light on the nature
of the letter position encoding deficit in LPD. Two options
are imaginable: incorrect position encoding and underspecified
position. If the nature of the letter position deficit is incorrect
encoding of letter positions, the word with the incorrect positions
is identified in the orthographic input lexicon according to the
incorrect information that arrived from the orthographic-visual
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Güven and Friedmann Letter Position Dyslexia in Turkish
0
10
20
30
40
50
60
70
T.E.K. F.A. M.L. A. B.A. C.G. S.U. D.Ç. U.S. S.Y. M.K. M.C. S.S. M.B. B.K. E.K. D.Ö. B.Y. Z.E.K. E.A. Z.E.S. S.A. İ.Ç. G.E. Control
Group
Average
Lexical Decision Same-Different Comprehension
FIGURE 6 | Percentage errors of each of the LPD participants on the three silent reading tasks in comparison to the control group (control data reported in the
rightmost columns).
analyzer and no effect of frequency is expected. If, however, the
nature of the letter position encoding deficit is that the position
of some (usually middle) letters is not encoded, frequency should
affect the error rates. This is because letter position is encoded at
a stage before the orthographic input lexicon, and partial position
information that is transferred to the orthographic lexicon, which
is organized by word frequency, should first activate the more
frequent word of the migratable word pair. Thus, according to the
partial letter position encoding hypothesis, when the target word
is less frequent than its migration counterpart, the less frequent
word is expected to be read as the more frequent one; the more
frequent target word is expected to be read with fewer migrations.
Method
In order to examine the effect of frequency on letter migrations
in children with LPD, we wanted to use a frequency rating that is
appropriate for their age and their familiar world. We, therefore,
collected frequency ratings from 30 typically-developing children
in the same age and classes as our LPD participants. We presented
them with 305 pairs of migratable word pairs – the target word
we used in the test and its possible migration result. We asked the
children to judge, for each pair, which of the two words was more
familiar to them, and occurred more frequently in what they read.
We collected their judgments and defined, for each pair, which
word was more frequent. Then, we selected the target-response
pairs for which there was a clear frequency difference.3
Results
The results indicated that there were far more migrations when
the target word was clearly less frequent than the migration
result (21.2% migrations on the average) than when the target
3We defined a target word as “clearly more frequent than its transposition
counterpart” if [number of judges who judged the target as more
frequent/(2∗number of judges who judged the response as more
frequent +number of judges who judged the target and response as having
similar frequency)] was larger than 1. We followed the same procedure for
selecting response words as clearly more frequent.
word was clearly more frequent than its migration result
(9.0% migrations on average). This comparison was significant
(Wilcoxon z = 4.24, p<0.0001, r= 0.61).4This indicates that
frequency affects migrations and supports the partial position
encoding hypothesis.
NUMBER READING
To examine whether LPD results from a general visual/perceptual
deficit or whether it rather pertains to orthographic material
only, we examined the LPD children’s reading of multi-digit
numbers. We presented 40 multi-digit numbers (2–4 digits long,
M= 3.1 digits, SD = 0.8), and asked the participants to read
each number aloud.
Results
The LPD participants, who made a considerable rate of
migrations in reading words, made very few migration errors
when they read numbers. They made only 0.25% migration errors
in reading multi-digit numbers aloud. Of the 24 children, 21
made no digit migrations at all in reading numbers, and three
children made a single digit migrations error. This migration rate
in numbers was significantly smaller than the rate of migrations
that the same children made in reading words, Wilcoxon z = 6.18,
p<0.0001, r= 0.89. This remains a significant difference if we
only take digit migrations in the 15 4-digit numbers (0.3%) and
compare them to letter migrations in the 4–5 letter words (9.5%),
Wilcoxon z =6.11,p<0.0001, r= 0.89 (as we have seen above,
there is no length effect in migrations in word reading, and the
4A different level of familiarity, familiarity at the bigram level, did not seem to
affect the participants’ errors. We calculated the bigram frequency of each of the
target words in the screening test and the migratable word list that yielded a
transposition response, and the bigram frequency for the transposition responses
(bigram frequencies taken from Sak et al., 2008). There was no significant
difference in bigram frequencies between the target words and their migration
responses, t(452) = 0.70, p= 0.48.
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Güven and Friedmann Letter Position Dyslexia in Turkish
rate of migrations is identical in 4-, 5-, and 6 letter words). The
comparison of digit migrations to letter migrations in non-words
yielded a similar result: the LPD group made significantly more
letter migrations in migratable non-words (M= 18.38, SD = 0.10)
than digit migrations in numbers (M= 0.38, SD = 0.01), Wilcoxon
z= 6.15, p<0.0001, r= 0.89.
There was no significant difference between the rate of digit
migrations in the LPD group (M= 0.13, SD = 0.33) and in the
control group (M= 0.22, SD = 0.42) (in fact, the LPD group
even had a slightly smaller digit migration rate than the controls),
t(50) = 1.07, p= 0.28. As 21 of the LPD participants made no
digit migrations at all and 3 LPD participants made a single digit
migration, none of the LPD participants differed from the control
group in number reading.
DISCUSSION
This study identified a first specific type of developmental
dyslexia in Turkish, developmental LPD. This is the first
report of LPD in Turkish, and it joins reports of LPD in
Hebrew, Arabic, and English (Friedmann and Gvion, 2001,
2005;Friedmann and Rahamim, 2007, 2014;Friedmann et al.,
2010, 2015;Friedmann and Haddad-Hanna, 2012, 2014;Kohnen
et al., 2012;Kezilas et al., 2014), enriching our understanding
of this dyslexia and its characteristics. It also joins a growing
body of evidence showing that not only acquired dyslexia,
but developmental dyslexia also has various types (for reviews
see Marshall, 1984;Castles and Coltheart, 1993;Castles, 2006;
Coltheart and Kohnen, 2012;Castles et al., 2014;Hanley, 2017;
Friedmann and Coltheart, 2018).
Turkish Dyslexics Do Make Errors in
Reading Aloud, Once the Appropriate
Stimuli Are Presented
It is especially interesting that this dyslexia was found in Turkish,
in light of the fact that researchers of dyslexia in Turkish
claim that dyslexia only manifests itself in fluency impairments
(Erden et al., 2002;Özmen, 2005). In fact, Raman (2011)
and Ergül (2012) claimed that Turkish-speaking children with
dyslexia read accurately (their accuracy was age-appropriate)
but their reading fluency is below the normal level. These
suggestions follow a tradition of dyslexia research suggesting
that in languages with transparent/consistent orthographies,
individuals with dyslexia do not make errors but can only
be detected on the basis of their lower reading speed
(e.g., Wimmer, 1993).
We believe that the generalization that dyslexic readers of
transparent orthographies do not make reading errors is a
misconception. First, the transparency of an orthography should
only affect the rate of errors in oral reading in cases of surface
dyslexia. Namely, individuals with an impairment in the lexical
route, who are forced to read words via the sublexical route, are
expected to make fewer errors in reading words if the grapheme-
to-phoneme conversion is consistent and often provides the
correct reading. However, crucially, surface dyslexia is only one
of 21 types of dyslexia, and the orthographic depth of a language
is not expected to affect the other types of dyslexia. Additionally,
different dyslexias yield different types of errors and are affected
by different dimensions of words. Therefore, to identify each type
of dyslexia, the relevant stimuli need to be presented, otherwise,
the person with dyslexia will not make reading errors. Therefore,
for example, to detect surface dyslexia, one needs to present
irregular words; to detect phonological dyslexia, one needs to
present non-words, and to detect deep dyslexia one needs to
present function words, abstract words, and morphologically
complex words. To detect LPD, one needs to present migratable
words, i.e., words in which letter migration creates other existing
words. And indeed in this study, we presented to the Turkish
reading dyslexics migratable words and non-words and they
made migration errors in reading, sometimes even up to 30%
of the words (on migratable words that allowed for consonant
migration) and to 47% of the migratable non-words.
The participants made far more errors on migratable words
(and non-words) than on non-migratable words (and non-
words). In fact, they did not make migrations on the non-
migratable words. This finding is in line with the lexical tendency
that the participants showed in their migration responses: most
of their migration responses (in reading the migratable word
and the migratable non-words) were lexical. This means that the
diagnosis of LPD in Turkish critically hinges on the types of
words that are presented to the participant: if migratable words
are not presented, the participant’s LPD may be missed.
Through the analyses of these migration errors, the study
examined, in detail, the characteristics of LPD and the way
it manifested itself in Turkish. We found that many of the
characteristics of LPD reported for other languages held also
for our Turkish-speaking participants more middle than exterior
letter migrations, slightly more adjacent than non-adjacent
migrations, and we were also able to discover new properties,
which the special nature of the Turkish language and orthography
allowed us to examine. Below, we report and discuss the main
properties of LPD in Turkish that emerged from this study.
No Effect of the Morphological Structure
of the Word
Turkish has very rich morphology, which made it a wonderful
testing ground for examining the effect of morphology on letter
position encoding. We examined several points regarding the
interaction of morphology and letter position encoding. First,
we asked whether more migrations occurred in morphologically
complex words compared with morphologically simple ones. The
results were that there were no differences between the rates
of migrations in morphologically complex and morphologically
simple words.5In addition, many of the migrations changed the
morphological structure of the target word. The migrations were
also insensitive to whether the letters belonged to the stem or
5This pattern differs from other types of dyslexia where morphologically complex
words are more prone to errors. For example, Çapan (1989) reports on two
Turkish children with dyslexia who made more errors on longer words and made
many omissions in morphologically complex words. Their deficit may have been
in the orthographic input buffer or the phonological output buffer, stages that
are sensitive to the morphological structure of the target word (Sternberg and
Friedmann, 2007;Dotan and Friedmann, 2015).
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Güven and Friedmann Letter Position Dyslexia in Turkish
the affix: the participants actually made more transpositions of
letters of the stem with letters from the non-stem morpheme than
within-morpheme migrations.
These findings suggest, in line with Friedmann et al. (2015),
that letter position encoding precedes morphological analysis,
a conclusion that is quite sensible: to perform morphological
analysis, the system needs to know first exactly where each
letter is localized.
Migrations Are Sensitive to the
Consonant-Vowel Status of the
Migrating Letters
In a recent paper, Khentov-Kraus and Friedmann (2018) reported
on vowel dyslexia, which selectively affects the reading of
vowel letters. This dyslexia results from a selective deficit in
the processing of vowel letters in the sublexical route. In the
framework of that paper, the researchers also analyzed migration
errors of 48 Hebrew readers with LPD and found that they make
more errors that involve the transposition of two consonants than
transpositions of a vowel and a consonant. This, in turn, was
taken to suggest that the orthographic-visual analyzer is already
sensitive to the consonant-vowel status of the target letters. In
the current study we took this examination one step further, by
using the opportunities offered to us by the Turkish language and
orthography. We compared CC transpositions (transpositions
of a consonant letter with another consonant letter), with CV
transpositions (transpositions of a consonant letter with a vowel
letter), and added a comparison that has not been done yet, of
VV transpositions – transpositions that only involve two vowels
exchanging positions. We did so by selecting three types of
migratable words, each allowing different types of transposition.
The results were clear-cut: CC migrations occurred almost
three times more than either VC or VV migrations. This finding
applies also to non-words, where most of the migrations involved
consonants only. This finding has a very important bearing on
the orthographic-visual analyzer: it means that already at the
stage of letter position encoding, the orthographic-visual analyzer
is sensitive to the consonant-vowel status of the letter. Namely,
even though consonant and vowel are phonological notions, the
orthographic processing is sensitive to this distinction at the letter
level, and distinguishes between consonant letters and vowel
letters already at the orthographic-visual analysis stage, long
before the phonological stages of reading.
This difference between migrations of consonant and vowels
also says something about the nature of the LPD deficit: it is not
a visual deficit, but rather a deficit in a later, orthographic stage.
Had the deficit been visual, no difference between consonant and
vowel letters would be predicted.
The finding that there were mainly CC migrations also
accounts for the finding that more migrations occurred between
syllables than within a syllable: syllable structure in Turkish is
regular, and syllables take the forms CV, VC, CVC, and VCV.
As a result, migration within a CV or VC syllable will always
be CV migration, whereas migration across syllables can be CC
migration. The tendency to make more CC migrations results in
making more across-syllables migrations.
The Locus of the Deficit That Gives Rise
to LPD
The Deficit Is in a Stage Shared by the Lexical and
Non-lexical Routes: Non-word Reading
We tested the participants’ reading, not only of existing words
but also of non-words. This is important in order to examine
whether the deficit indeed lies in the orthographic-visual analyzer
or whether it stems from a deficit in the orthographic input
lexicon. We found that the participants made migration errors
not only on words but also on (migratable and non-migratable)
non-words, and that their non-word reading shows the same
error types (migrations) and the same characteristics as word
reading. These findings indicate that the deficit that gives rise
to LPD has to reside in a non-lexical stage that is shared by the
lexical and sublexical routes.
The Deficit Is in an Input Reading Stage and Not in a
Phonological Output Stage
Two such shared stages exist the orthographic-visual analyzer
and the phonological output buffer. Which of them is
responsible for LPD? If the deficit lies in the orthographic-
visual analyzer, then the deficit should not only affect
reading aloud but also other tasks that involve reading
input, even without oral production. If the deficit is in the
phonological output buffer, silent reading tasks should not
involve migrations. To examine this, we tested the participants’
same-different decision, lexical decision of migratable non-
words, and the comprehension of migratable words that
required distinguishing between the target word and its
migration counterpart.
We found that all the LPD participants had letter migrations
not only in oral reading but also in at least one of these silent
reading tasks. These results support the localization of the deficit
in the orthographic-visual analysis, pre-lexical stage.
To further explore this point, and examine the phonological
output buffer stage, we also asked them to repeat the
migratable words they had read with a migration error.
Had the deficit originated in the phonological output stage,
we would expect the participants to also make these errors
when they repeated the same words. The results unequivocally
showed that they were unimpaired in the phonological output
stage – they repeated the migratable words correctly, and
significantly better than their reading of the same words.
We reached the same conclusion on the basis of a non-
word repetition task in which these participants performed
within the normal range, again, ruling out a deficit in
their phonological output stage. Additionally, the finding that
there was no significant length effect on migrations also
supports the conclusion that the deficit does not reside in the
phonological output buffer.
To conclude, then, the results indicate that the participants’
deficit that gives rise to LPD is in the orthographic-visual
analyzer, in the function responsible for letter position encoding.
This function is already sensitive to the consonant-vowel status
of the target letters but is not sensitive to the morphological
structure of the target word.
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Güven and Friedmann Letter Position Dyslexia in Turkish
Letter Positions Are Underspecified,
Rather Than Incorrectly Encoded:
Evidence From the Frequency Effect
The frequency had a significant effect on migrations. The
participants made far more migrations when the target word
was less frequent than the migration result than when the target
word was more frequent than its migration result. This, too, has
implications for diagnosis, as well as for the description of the
LPD impairment. Clinically, it means that in order to detect LPD,
it is better to present the less frequent migratable word than its
more frequent counterpart. Theoretically, it provides insights as
to the nature of the impaired process in LPD.
One can imagine two possibilities for the failure in letter
position encoding: one is that letter identities are bound to
incorrect letter positions, the other is that the position of some
(usually middle) letters is not encoded. These two descriptions
bear different predictions with respect to the effect of frequency
on migrations: if it is erroneous letter position encoding, the
input to the orthographic input lexicon is letters that appear in
an incorrect order, and if this letter order exists in the lexicon,
it doesn’t matter how frequent it is, so we would not expect
frequency to affect the errors. If, on the other hand, frequency
does have an effect, as we see here, it means that letter positions
are not encoded and then the lexicon is searched with this partial
information, of letter identities without positions. In this case,
the orthographic input lexicon finds the first lexical entry that
matches the partial information, which will usually be the more
frequent word. Thus, the frequency effect we detected suggests
that our participants did not encode the position of some of the
letters, rather than encoded it incorrectly.
Not a General Deficit in Sequence
Perception: Normal Number Reading
Another question that is often raised with respect to LPD is
whether it is dyslexia that affects only orthographic material or
whether it is a more general perceptual deficit that also affects
other sequences. To examine this, we tested our participants’
reading of multi-digit numbers. We found that none of the
participants had a deficit in reading numbers and none of them
made more digit migrations than the controls.
This indicates, in line with other studies on LPD (Friedmann
et al., 2010) and on other dyslexias in the orthographic-
visual analyzer (see Dotan and Friedmann, 2019, for a
review of dissociations between dyslexia and dysnumeria),
that the orthographic-visual analyzer is orthographic-specific
and does not handle digits. It further indicates that LPD is
orthographic-specific.
Theoretical Implications for the Reading
Model
These results bear theoretical implications for the word reading
process. Firstly, the finding that letter migrations were unaffected
by the morphological structure of the target word suggests
an insight with respect to the relative order of letter position
encoding and morphological analysis. It indicates that letter
position encoding happens before the system can parse the
morphological structure of the target word. This makes sense, as
morphological analysis needs to apply to strings of letters that are
already bound to positions within the word.
A second theoretical implication regards the processing of
consonant and vowel letters. The findings that consonant
transposed with other consonants far more often than
consonants with vowels, and that consonants migrated more
than vowels, indicate that the consonant-vowel status of the letter
is already computed early in the orthographic-visual analysis
stage, before letter position encoding. This finding also suggests
that the position of consonant and vowel letters is encoded
separately. The finding that consonant-consonant migrations
were far more frequent than consonant-vowel migrations, which
was also found in Khentov-Kraus and Friedmann (2018) for
Hebrew, can be accounted for by assuming that consonant
letters and vowel letters are encoded in two separate layers – a
consonant-letters layer and a vowel-letters layer, in which the
letters are ordered by their position. If we assume that migrations
occur more readily within a layer, this would account for
more consonant-consonant than consonant-vowel migrations.
However, the new finding from Turkish LPD, that there are
also more consonant-consonant migrations than vowel-vowel
migrations suggests that the position of consonant letters and
of vowel letters is encoded not only separately, but differently.
The view should probably not be that of two separate layers
of consonants and vowels, with migrations occurring mainly
layer-internally. It possibly suggests that the position of the
consonants in the word is computed first, creating an ordered
consonantal skeleton, and then each vowel letter is inserted
into the consonant skeleton. Under such mechanism, LPD
mainly affects the position encoding of the consonants in the
consonantal skeleton.
Finally, as we summarize above, the selective position-
encoding impairment, which affected letters but not digits,
indicates that the orthographic-visual analyzer is orthographic-
specific and does not handle digits (Friedmann et al., 2010;
Dotan and Friedmann, 2019).
Clinical Implications
Research on Turkish often refers to fluency as the only reading
aspect that is impaired in dyslexia, and possibly, as a result,
dyslexia studies only report fluency measures. Some researchers
conclude that Turkish readers with dyslexia do not make more
errors than controls (e.g., Raman, 2011). This study showed that
it is both possible and essential to also look at children’s errors.
To expose reading errors, it is crucial to present stimuli that
will be sensitive to each type of dyslexia and will induce the
relevant errors from the readers. In our case, it was migratable
words that were presented and revealed that Turkish readers
with dyslexia do make reading errors, once the appropriate
stimuli are presented to them. Our study shows that, in order
to diagnose LPD, the toolkit for diagnosis has to include
migratable words. We were able to identify this dyslexia because
we used the FR˙
IGÜ screening test, which we created to be
sensitive to the various types of dyslexia. To identify LPD, we
included in the test 121 migratable words and 22 migratable
non-words. These stimuli exposed the LPD of our participants.
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Güven and Friedmann Letter Position Dyslexia in Turkish
In contrast, the non-migratable words did not yield migrations.
This means that if we only used non-migratable words for
testing, we would have missed the source of reading difficulty
of our subjects.
Once the right stimuli are presented, it becomes possible to
diagnose persons with dyslexia not only on the basis of their
reading speed but also based on their error rates and the types
of errors that they make. This would be a way to explain to the
person with dyslexia what their problem is and to start targeting
treatment at the impaired components.
And in fact, slow reading is not as detrimental to reading
as are errors in reading. The parents who came with their
children for the reading tests reported to us only the fact that
the children were not reading correctly, and their concerns were
about their children making errors, in reading aloud and also
in understanding what they read. This applied more generally,
not only for the parents of children who we eventually found to
have LPD but also for children with surface dyslexia, attentional
dyslexia, and vowel dyslexia.
A further clinical conclusion related to the properties of the
migratable words selected for the diagnostic word list: in order
to trigger more errors, they should include two adjacent middle
consonants that may transpose and create another existing word,
which is more frequent than the target one.
Thus, the clinical implications of the current study are: (A)
look at errors and error types, and (B) use (less-frequent)
migratable words in the word lists for diagnosing LPD, and, in
general – include words that are sensitive to each dyslexia type in
order to identify it.
DATA AVAILABILITY STATEMENT
The raw data supporting the conclusions of this manuscript will
be made available by the authors, without undue reservation, to
any qualified researcher. The authors maintain the rights for the
reading tests.
ETHICS STATEMENT
This study was carried out in accordance with the
recommendations of Ethical Guideline of the Anadolu University
Ethical Committee with written informed consent from
all subjects. All subjects gave written informed consent in
accordance with the Declaration of Helsinki. The protocol was
approved by the Anadolu University Ethical Committee.
AUTHOR CONTRIBUTIONS
NF and SG conceived of the presented idea and designed the
experiments. Both authors constructed the stimuli together and
verified the analysis methods. NF supervised the project. SG
carried out the experiments. Both authors discussed the results
and wrote together the final manuscript.
FUNDING
This research was supported by the Anadolu University
Grant No. 1503E142, HFSP grant (no. RGP0057/2016,
Friedmann), and Branco-Weiss Chair for Child Development
and Education.
ACKNOWLEDGMENTS
We wholeheartedly thank the families of the participating
children for their participation in this study and are also grateful
for the help and guidance of the teachers in the schools in which
we tested these children. We thank ¸Sebnem Kele¸s, Özge Üçpınar,
and Nupelda Yalçınkaya for their help in data collection. We are
deeply grateful to the Language and Brain Lab members for their
feedback and helpful advice during the development of FR˙
IGÜ.
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