| A central issue in the biology of language is distinguishing invariant language functions from those that depend upon the particular modality through which language is perceived. While the majority of previous electrophysiological and neuroimaging research has focused on written language processing, reading is not the primary form in which we acquire and use language. From birth and throughout ones life, the majority of language is experienced through face-to-face interaction. The three studies presented in this dissertation examine sentence processing as it occurs in environmentally rich, primary modalities. In Chapter I, functional Magnetic Resonance Imaging was employed to measure neural activation when participants simultaneously heard and viewed the upper body of a speaker producing English sentences. The results show that the greater recruitment of the left than right perisylvian cortex found in studies of written and spoken language extends to audio-visual (AV) language processing. Similar to AV language, signed languages are a primary form of language. In addition, sign language provides a unique opportunity to look at language that is conveyed and perceived in a separate manner than written or spoken language. In Chapter II, Event-Related Brain Potentials (ERPs) were recorded to semantically and syntactically appropriate and anomalous American Sign Language (ASL) sentences in congenitally deaf native signers. Consistent with studies of written and spoken language processing, semantic anomalies elicited a central posterior N400, whereas syntactic violations elicited an anterior negativity followed by a P600. However, the distribution of the anterior negativity varied as a function of the type of syntactic agreement violation. In Chapter III, the same experimental paradigm was used to study ASL sentence processing in congenitally deaf signers who acquired ASL during childhood or during adolescence/early adulthood. ERPs to semantic processing were similar across groups. In contrast, early syntactic processing varied as a function of age of acquisition. These findings support the hypothesis that, for signed language, as for written and spoken languages, different linguistic subsystems display different patterns of developmental plasticity. Together, these findings point to the central role of biological constraints and the effects of experience in language development.; This dissertation includes co-authored materials. |
