Reading minds: How and where does orthographic processing occur in the brain?

Duñabeitia, J. A. 1 , Quiñones, I. 1 & Carreiras, M. 1, 2, 3

1 Basque Center on Cognition, Brain and Language (BCBL); Donostia
2 Ikerbasque, Basque Foundation for Science; Bilbao
3 Euskal Herriko Unibertsitatea; Bilbao

In alphabetic languages visual word processing requires relatively precise identification of the individual letters that constitute each word and of the position occupied by each letter within the string. After decades of intensive behavioral and neuroimaging research, the specific neural circuits recruited for alphabetic coding are still unclear. While some theoretical models propose that position-in-string coding responds to general flexible mechanisms of the visual system that are character-unspecific, recent results call into question this assumption. We will review recent evidence at this regard obtained from samples of developing readers (i.e., schooled children of different ages), illiterates, and adult expert readers, demonstrating that letter position coding responds to specific processes that are different from those that guide position-in-string assignment of other types of visual objects such as digits or symbols. Besides, we will demonstrate that the emergence of letter-specific coding mechanisms is closely linked to the literacy process. Finally, we will present fMRI evidence demonstrating that clearly differentiated brain areas respond more to letters than to other alphanumeric characters and vice versa (i.e., different brain pathways engaged in the processing of different types of visual characters), and that a specific region in the left hemisphere (the left parietal cortex) is particularly involved in letter identity and position coding.