Neural mechanisms underlying the processing of semantic ambiguity

This presentation will begin with a brief summary to our fMRI data acquisition method such as experimental paradigms that we usually employ to acquire brain images from the MRI scanner. It will then be followed by an introduction to previous research findings focusing on semantic processing - an important issue in neuroimaging research. In particular, the involvement of several brain regions such as the left inferior frontal gyrus (Petersen et al., 1989; Feiz, 1997; Wagner et al., 2001) and left mid-superior frontal regions (Fletcher et al., 1996; Scott et al., 2003) during various semantic tasks will be discussed.

Discussion on one of our recent studies on semantic ambiguity will be followed. In this study, we used a word generation paradigm to examine whether neuroanatomical networks for meaning are modulated by lexical ambiguity because previous studies typically utilize words having a precise and dominant meaning as stimuli and have not manipulated lexico-semantic ambiguity, a key feature of human language, as an experimental variable. We found that, compared with semantically precise words, semantically ambiguous words were mediated by strong brain activations in the left dorsal-lateral frontal areas, the anterior cingulate, and the right inferior parietal lobe. Semantically precise words, instead, were associated with the left inferior frontal and mid-superior temporal sites. These findings indicate that semantic analysis of written words is a dynamic process involving coordination of widely distributed neural subsystems, which are weighted by semantic ambiguity (Chan et al., 2004).

References

Chan, A.H.D., Liu, H.L., Yip, V., Fox, P.T., Gao, J.H., & Tan, L.H. 2004. Neural systems for word meaning modulated by semantic ambiguity. NeuroImage 22, 1128-1133.
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Fletcher, P.C., Shallice, T., Frith, C.D., Frackowiak, R.S., & Dolan, R.J., 1996. Brain activity during memory retrieval. The influence of imagery and semantic cueing. Brain 119, 1587-1596.
Petersen, S.E., Fox, P.T., Posner, M.I., Mintun, M., & Raichle, M.E., 1989. Positron emission tomographic studies of the processing of single words. J. Cogn. Neurosci. 1, 153-170.
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Wagner, A.D., Pare-Blagoev, E.J., Clark, J., & Poldrack, R.A., 2001. Recovering meaning: left prefrontal cortex guides controlled semantic retrieval. Neuron 31, 329-338.