Semantic Processing Without Conscious Understanding in a Global Aphasic: Evidence From Auditory Event-Related Brain Potentials

Abstract

We report a global aphasic who showed evidence of implicit semantic processing of spoken words. Auditory event-related brain potentials (ERPs) to semantically congruous and incongruous final words in spoken sentences were recorded. 17 elderly adults served as control subjects. Their ERPs were more negative to incongruous than to congruous final words between 300 and 800 ms after stimulus onset (N400), and more positive between 800 and 1500 ms (Late Positivity). The aphasic showed an exactly similar pattern of ERP components as the controls did, but his performance in a task demanding explicit differentiation between semantically congruous and incongruous sentences was at the chance level. During followup, his explicit understanding recovered over the chance level but the ERPs remained fairly similar. We conclude that implicit semantic activation at the conceptual level can take place even in the absence of conscious (explicit) comprehension of the meaningfulness of linguistic stimuli.