Electrophysiological exploration of semantic processing: the roles of expertise and sensory modality

Semantic memory consists of stored information about features and attributes that define concepts and the processes (Martin & Chao, 2001). The N400, an event-related brain potential (ERP) waveform, reflects process through which the meaning of an incoming stimulus is mapped onto the corresponding field in semantic memory (Sitnikova et al., 2003). In other terms, the amplitude of this component might index the difficulty to integrate the incoming information with previous information (Proverbio et al. 2010). Several previous studies revealed the sensitivity of the N400 to semantic violations related to a wide range of stimulus types across modality. However, it is still not clear how and when different types of semantic information are integrated in the brain. Therefore, this work aimed at investigating electrophysiological processing to semantic violations in different kinds of context. More specifically, we focused on the effects of experiences shaped by a specific motor training and/or based on world-knowledge. In particular, we investigated the effects of semantic violations on the amplitude and the morphology of the N400 component. In addition, we verified if the difficulty (or the ease) to integrate the incoming information into the semantic memory is also affected by the sensory modality of the information. To this aim, we carried out four studies in order to analyze these aspects. The results of the first study revealed that the N400 amplitude is modulated by the congruency of peculiar stimuli (faces) depicted in specific complex situations. The second study showed that the N400 response is sensitive to semantic violations in visual processing of actions related to a sport training. In particular, we observed that the N400 amplitude to violations was a function of the observers’ expertise. The results of the third study demonstrated that the semantic processing related to a long lasting musical training affected the N400 amplitude even when stimuli are presented using a multisensory modality. Indeed, we showed that incongruent action-sound presentations elicited a greater N400 amplitude in musicians compared to naïve participants. Finally, in the last work we showed that incongruent words that evoked specific sounds in comics modulated the N400 response in a group of University students with experience in reading comics. The results of this work revealed a cross-modal nature of the N400 showing that semantic violations to information characterized by differences in sensory modality elicited slightly different ERP scalp distributions. This evidence might suggest that the semantic processing of both world-knowledge and knowledge learned through a specific motor/artistic training might be affected by perceptual factors. In addition, the data showed that the N400 amplitude is affected by the level of expertise related to a specific knowledge. Indeed, we observed that the proficiency in a specific context modulated the brain response to semantic anomalies. Overall, these data revealed the effects of experience and the acquisition specific semantic knowledge on brain neuroplasticity.