Dissertation committee:
Μαριέττα Παπαδάτου-Παστού, Επίκουρη Καθηγήτρια, Παιδαγωγικό Τμήμα Δημοτικής Εκπαίδευσης (Π.Τ.Δ.Ε.), Εθνικό και Καποδιστριακό Πανεπιστήμιο Αθηνών (Ε.Κ.Π.Α.)
Φίλιππος Βλάχος, Καθηγητής, Παιδαγωγικό Τμήμα Ειδικής Αγωγής, Πανεπιστήμιο Θεσσαλίας
Nicholas A. Badcock, Senior Lecturer, School of Psychological Science, University of Western Australia
Ευαγγελία Μαυρικάκη, Καθηγήτρια, Π.Τ.Δ.Ε., Ε.Κ.Π.Α.
Φαίη Αντωνίου, Αναπληρώτρια Καθηγήτρια, Παιδαγωγικό Τμήμα Δευτεροβάθμιας Εκπαίδευσης, Ε.Κ.Π.Α.
Αλεξάνδρα Οικονόμου, Καθηγήτρια, Τμήμα Ψυχολογίας, Ε.Κ.Π.Α.
Sebastian Ocklenburg, Professor, Department of Psychology, MSH Medical School
Summary:
This thesis delves into the cerebral lateralization for written language, a domain
overshadowed by the extensive research on oral language lateralization. While it is well established that the left hemisphere is dominant for oral language in the majority of individuals, investigations into written language lateralization, particularly in left-handers, remain sparse. In parallel, individuals with conditions that are associated with writing difficulties, such as specific language disorder, and, of particular importance for this thesis, dyslexia, remain neglected in terms of studying their lateralization for written language. It has been shown that dyslexia is associated with a more symmetrical or right lateralized pattern for reading and oral language, which can be reorganized following an appropriate educational intervention. Writing involves both language and motor components, jointly contributing to cerebral activation, yet prior research has not effectively disentangled these elements.
The three studies in this thesis built upon one another and aimed to disentangle the
language and motor components of writing lateralization by comparing cerebral activation during (i) written word generation and (ii) letter copying. Cerebral lateralization was measured using functional transcranial Doppler (fTCD) ultrasound and the strength of the evidence was assessed using the Bayesian approach. For the first study, an adult sample balanced for handedness was recruited (n = 60), and preregistered hypotheses anticipated (a) weaker cerebral lateralization for the linguistic component in left-handers compared to right-handers, and (b) a lack of correlation between oral language and the linguistic component of written language in terms of cerebral lateralization. However, the findings did not provide compelling evidence for either hypothesis, underscoring the intricate processes involved in both written and oral language. For the second study, 7- to 9-year-old children at risk for dyslexia (n = 12) were compared with age-matched typically developing peers (n = 24) in terms of the lateralization for the linguistic component of written language and it was hypothesized that the linguistic component of written language would be less left-lateralized in children at risk for dyslexia than in controls, but there was inadequate evidence to support this hypothesis. Additionally, the study explored correlations between writing competence, handwriting quality, orthography, and cerebral lateralization, revealing a lack of evidence for such correlations. For the third study, which was a pilot study (n = 5 children at risk who were administered a phonological intervention compared to n = 5 age-matched, gender-matched, and intelligence-matched peers), the aim was to explore the impact of a phonological intervention on the cerebral lateralization of the linguistic component of written language in children at risk for dyslexia. A pragmatic intervention was also tested for feasibility. Although the phonological intervention was hypothesized to induce a leftward shift in cerebral lateralization, the findings did not decisively support or refute this hypothesis.
Collectively, these findings suggest that, despite a predominant left lateralization for
written language among most participants, factors such as handedness, age, and proficiency in reading and writing moderate this pattern. Furthermore, this thesis confirmed that fTCD lends itself to measure cerebral lateralization in adults and also extended this practice to children as young as 7 years old, while emphasizing the difficulty in devising a control task that effectively isolates the motor component of writing. Overall, the outcomes derived from this series of studies carry potential implications for the importance of including written language in
language lateralization studies when assessing the typical brain, as well as in the context of special learning difficulties, such as dyslexia. Finally, the present thesis underscores the impact of educational interventions on reading performance and how this is reflected in the cerebral lateralization for written language
Keywords:
language lateralization, cerebral lateralization, writing, handedness, dyslexia, intervention
