Although our understanding of the brain bases of semantic interpretation is beginning to be detailed at the level of individual lexical items, the neural mechanisms by which complex meanings are composed are still entirely unknown. With National Science Foundation support, Dr. Pylkkanen will conduct a three-year investigation aimed at elucidating the spatio-temporal dynamics of complex meaning composition. Brain activity will be measured with magnetoencephalography (MEG), which offers the best combination of spatial and temporal resolution of currently available cognitive neuroscience methods. One of the most fascinating features of human language is that many meanings are not expressed overtly. For example, when a sentence such as "the boy shut the door tight" is encountered, all English speakers immediately and automatically know that this sentence describes a causal relation between an event of shutting and a state of tightness even though no overt element in the sentence describes causality. Further, all speakers converge on the interpretation that the state of tightness does not hold of the explicitly mentioned door, but rather of some unmentioned closure between the door and its frame. This project focuses on the interpretation of covert meaning, as it offers a unique opportunity to study semantic composition while largely eliminating phonological and syntactic processing. The project covers multiple levels of representational complexity and involves three sets of studies: one investigating covert complexity in individual lexical items that appear to be simple, another on the effect of semantic opacity in the processing of overtly complex words such as "sweat-er", and a third on covert meaning composition at the sentence level. The project represents a novel type of combination of cognitive neuroscience methodology with detailed representational hypotheses emerging from theoretical linguistics, reflecting Dr. Pylkkanen's combined training in the two fields. An integral part of this research is bringing together a diverse group of students and faculty from linguistics, psychology and medical and/or neuroscience backgrounds. Finally, the clinical applications of the project are potentially substantial. Semantic impairment characterizes a vast array of neurological disorders, including aphasias, schizophrenia, developmental disorders such as autism, and neurodegenerative diseases. A prerequisite for understanding semantic malfunction is first understanding how the healthy brain accesses and computes meaning.
