Investigation of semantic effects in oddball paradigm through event related potentials

Dumlu, Seda Nilgün
In this study, the effect of semantic information processing was investigated by the oddball paradigm, by presenting consecutive Turkish words or word-like non-words while EEG signals are recorded. In an oddball paradigm, a series of events are presented of which one class is rarer than the other. Subjects are asked to respond to the infrequent stimuli (e.g. press a button, or count the number). The event related potential (ERP) component P300 obtained from EEG is considered as the marker of this attention capturing paradigm. P300 is obtained consistently for both visual and verbal stimulus. On the other hand, the ERP component N400 is consistently associated with semantic processing in neurolinguistics. Additionally, Late Positive Component (LPC) is a marker for the top-down attention mechanism during word comprehension. Moreover, there are other components, called early ERPs, which occur between 100-200 ms after the stimulus onset. These components orthographically and phonologically reflect low-level features of words. The target words chosen for our study are strictly limited to belong to a neutral category and not consist of any emotional content, to rule out emotional interference in semantic processing. Based on the ERP components that were obtained from this study, the LPC potential exhibited for words had higher amplitude than that of non-words consistently and statistically significantly. However, our study was confounded with the heterogeneity of non-words because some of the non-words were non-sense letter sequences while others were pseudowords. Due to this, although we observed the P300 and N400 ERPs consistently for all stimuli, we did not find significant differences for these potentials between words and non-words. To the best of our knowledge, our investigation is one of the few studies conducted with EEG recordings in a task that involved lexical decision making in Turkish.


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Citation Formats
S. N. Dumlu, “Investigation of semantic effects in oddball paradigm through event related potentials,” M.S. - Master of Science, Middle East Technical University, 2012.