Electroencephalography and Clinical Neurophysiology/Evoked Potentials Section

Forty-four right-handed volunteers were invited to listen to Italian 5-letter words of different kinds, including non-words, digitally recorded. Signals from 16 electrodes were averaged and displayed both as traces and maps. When the same word was monotonously delivered to the subject, a positive component at 340 ms was recorded following the N100–P200 complex. This potential was automatic, phonologically driven, independent of habituation, specific for verbal material and lateralized to the left side. By contrast, semantic tasks evoked bilateral N400, by using the oddball paradigm with different kinds of target stimuli, including non-words. The N400 duration was related to the task complexity. The late positive component was locked-in-time with the end of the words. Therefore, N400 reached its peak before the word completion. At that time the probability of recognition was 60%, progressively reaching 100% at the time of the late positive component. Intra- and interindividual variance was low. The findings indicates two different language processings: one is confined to the perisylvian regions of the left hemisphere in right-handed subjects and appears earlier, reflecting phonological processing, whereas the other one is bilateral and takes places when semantic judgments are going on. Event-related potentials during language processing appear to be a very useful tool, especially when EEG maps are displayed, giving us the information on both temporal and spatial events.