The neurotopography of written word production: An fMRI investigation of the distribution of sensitivity to length and frequency

This research is directed at charting the neurotopography of the component processes of the spelling system by using fMRI to identify the neural substrates that are sensitive to the factors of lexical frequency and word length. In spelling, word frequency effects index orthographic long-term memory whereas length effects, as measured by the number of letters, index orthographic working memory (grapheme buffering). Using the task of spelling to dictation in the scanner, we found a highly differentiated neural distribution of sensitivity to the factors of length and lexical frequency, with areas exhibiting sensitivity to length but not frequency and vice versa. In addition, a direct comparison with the results of a previous study [Rapp, B., & Lipka, K. The literate brain: The relationship between spelling and reading. Journal of Cognitive Neuroscience, 23, 1180-1197, 2011] that used a very different spelling task yielded a converging pattern of findings regarding the neural substrates of the central components of spelling. Also, with regard to relationship between reading and spelling, we replicated previous functional neuroimaging studies that have shown overlapping regions of activation in the left posterior inferior frontal gyrus and midfusiform gyrus for word reading and spelling.