Design and evaluation of a Turkish paradigm for investigating verbal event-related potentials

Objective: This thesis investigated the electroencephalography (EEG) signals involved in processing semantically congruent and incongruent Turkish sentences. The aim was twofold: first, to evaluate the effect of such linguistic stimuli on cognitive processing; and second, to develop a valid and applicable paradigm that would allow analyses to be performed on the N400 and P600 event-related potential (ERP) components. Method: Thirty-five healthy native Turkish-speaking adults participated in the study. Participants were visually presented with sentences whose last word ended in a semantically compatible or incompatible manner. EEG recordings were acquired with a BrainVision BrainAmp device and preprocessing steps were performed using Brainstorm software. In the ERP analyses, N400 (300-500 ms) and P600 (500-900 ms) time intervals were evaluated and time-frequency analyses were performed with Morlet wavelet transform Results: Results showed that incongruent sentences elicited higher amplitude N400 responses than congruent sentences and that this difference was particularly concentrated in temporal-parietal regions. The P600 component reflected linguistic restructuring processes with increased positive amplitude in incongruent conditions. Time-frequency analyses showed that incongruent sentences were associated with higher power in the delta and alpha bands at the N400 time interval, whereas they produced lower power in the gamma-2 band. In the P600 time interval, increased power was observed for incongruent sentences only in the delta band; no significant difference was found in the other frequency bands. Conclusion: The findings show that violations of semantic integrity in Turkish have significant effects on the N400 and P600 ERP components. This study contributes to the literature as one of the limited number of studies documenting EEG patterns related to semantic processing in Turkish. In addition, the paradigm developed may serve as a reference for future cognitive neuroscience-based ERP studies.