Electrophysiological dissociation between verbal and nonverbal semantic processing in learning disabled adults

Event-related potentials (ERPs) were recorded as 16 adults with learning disabilities (LD) and 16 controls were presented with two sets of stimuli. The first set comprised pairs of line drawings and environmental sounds (nonverbal condition); the second consisted of printed and spoken words (verbal condition). In the controls, semantically related items elicited smaller N400s than unrelated items in both conditions, with opposing hemispheric asymmetries for spoken words and environmental sounds. The LD group did not show a significant difference between related and unrelated words, despite a robust context effect for nonspeech sounds. The results suggest anomalous processing limited to the verbal domain in a simple semantic association task in the LD group. Semantic deficits in this group may reflect a relatively specific deficit in forming verbal associations rather than a more general difficulty that spans both verbal and nonverbal domains.