Experimental Psychology - Learining & Development Seminar: Morphological decomposition with the ventral stream: a representational similarity approach

Morphology reflects one of the few systematic relationships between orthography and semantics, as letter combinations known as affixes are able to systematically modify the word meaning (e.g. un-: unlock, unable, unsure). Morphological information is accessed rapidly during skilled reading, and research has shown that morphological analysis arises at different levels, based on orthographic and semantic overlap (Gold & Rastle, 2007). We used representational similarity analysis to localise and characterise neural representations of morphologically complex words within the ventral stream, a proposed pathway in which the reader extracts semantic meaning using increasingly large orthographic units (Dehaene et al., 2005). We constructed a priori matrices, which expressed precise cognitive predictions about the similarity of words based on varying orthographic, morphological and semantic overlap. We expected these overlapping properties to elicit different patterns of activation at different levels of the hierarchically organized ventral stream pathway. Participants then silently read these words while we recorded neural responses using fMRI. Our analyses included region of interest and whole-brain searchlight analyses to explore morphological representations throughout the reading network. Our results inform our understanding of the transformation of form to meaning in visual word recognition, and provide evidence of a graded hierarchy of abstraction within the ventral stream.

Dehaene, S., Cohen, L., Sigman, M. & Vinckier, F. (2005). The neural code for written words: a proposal. Trends in Cognitive Sciences, 9(7), 335-341. doi: 10.1016/j.tics.2005.05.004.

Gold, B. T., & Rastle, K. (2007). Neural correlates of morphological decomposition during visual word recognition. Journal of Cognitive Neuroscience, 19(12), 1983-1993. doi: 10.1162/jocn.2007.19.12.1983.