Developmental Letter Position Dyslexia in Turkish, a Morphologically Rich and Orthographically Transparent Language

Abstract

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.

Vowel dyslexia in Turkish: A window to the complex structure of the sublexical route

“…We were also able to identify surface dyslexia in the reading of five of our vowel dyslexia participants. These two developmental dyslexia types join a recent paper [ 24 ] that reported on another type of developmental dyslexia in Turkish: developmental letter position dyslexia , which selectively impairs the encoding of letter position within words.…”

“…The results of this study bear theoretical implications for the word reading process. In a recent study, Güven and Friedmann [ 24 ] studied letter position dyslexia in Turkish and found that individuals with letter position dyslexia make significantly more transpositions of consonants with other consonants than of consonants with vowels, and of vowels with vowels. Given that letter position dyslexia is a deficit in letter position encoding, in the early stage of orthographic-visual analysis, this finding suggests that the consonant-vowel status of a letter is already available at the early stage of orthographic-visual analysis.…”

“…Additionally, once the appropriate stimuli have been presented, in this case, irregular words, there were five children with surface dyslexia who also made phonologically plausible errors in the reading of irregular words, i.e., surface dyslexia errors. Similarly, the participants with developmental letter position dyslexia in Güven and Friedmann [ 24 ] made letter position errors, especially when they were presented with migratable words.…”

“…There are very few studies on types of developmental dyslexia in Turkish. In a recent study, Güven and Friedmann [ 24 ] investigated letter position dyslexia in Turkish, a specific type of dyslexia that results from a deficit in letter position encoding, causing letter transpositions within words [ 9 , 25 – 30 ]. One other study described acquired dyslexia in Turkish which apparently affected the phonological output stages [ 31 ].…”

The Effect of Syntactic Impairment on Errors in Reading Aloud: Text Reading and Comprehension of Deaf and Hard of Hearing Children

“…This stage is responsible for letter identification, letter position encoding, and letter-to-word binding. The reading test indicated that participants YAZM and AVCM had letter position dyslexia and attentional dyslexia, which cause letter migrations within and between words, respectively [ 74 , 75 , 76 , 77 , 78 ], as well as vowel dyslexia, which causes errors in reading vowel letters [ 79 ]; Participants LIHF and CHBM had a more generalized deficit in the orthographic input buffer, resulting in letter migrations within and between words as well as letter omissions and substitutions in long words and nonwords, and morphological errors in reading [ 66 , 80 ]; LIHF also had surface dyslexia.…”