The role of semantic expectation versus written words stimuli involvement in N400 onset: A patented psychoverbal stimulation interface for EPs and reaction time recordings

The experiments used a patented psycho-verbal stimulation interface to study the origin of cognitive visual N400 evoked potential onset in reading process. The acquisition was performed in Oz, Pz, Cz, Fz leads, on a group of 50 normal persons, in two experiments. First experiment aims to probe the automatic origin of N400 by delivered each 500 words-lists at short asynchronic stimulation 200 ms and long asynchronic stimulation 1000 ms in a letter recognition task. Second experiment proposes to test the role of words expectancy in N400 onset by a letter recognition task at words semantic selected. Grand AVG function was used on each experiment for the average-group recordings at each task and statistic SPSS software based on ANOVA method was used to compare the differences in amplitude of N400. We observed overlapping traces for both acquisitions: at short asynchronic stimulation 200 ms and long asynchronic stimulation 1000 ms. Between the two tracks there is no difference amplitude and N400 wave is present. N400 elicited at unexpected words-list a prove to be a pronounced negativity between 350-450 ms and expected stimuli has produced no N400 effect, but a slight positivity between 350-500.