Letter representations in writing: an fMRI adaptation approach

Olivier Dufor,Brenda Rapp

doi:10.3389/fpsyg.2013.00781

Olivier Dufor, Brenda Rapp

Open Access

https://doi.org/10.3389/fpsyg.2013.00781

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Abstract

Behavioral and neuropsychological research in reading and spelling has provided evidence for the role of the following types of orthographic representations in letter writing: letter shapes, letter case, and abstract letter identities. We report on the results of an fMRI investigation designed to identify the neural substrates of these different representational types. Using an fMRI adaptation paradigm we examined the neural distribution of inhibition and release from inhibition in a letter-writing task in which, on every trial, participants produced three repetitions of the same letter and a fourth letter that was either identical to (no-change trial) or different from the previous three (change trial). Change trials involved a change in the shape, case, and/or identity of the letter. After delineating the general letter writing network by identifying areas that exhibited significant neural adaptation effects on no-change trials, we used deconvolution analysis to examine this network for effects of release from inhibition on change trials. In this way we identified regions specifically associated with the representation of letter shape (in the left SFS and SFG/pre-CG) and letter identity [in the left fusiform gyrus (FG)] or both [right cerebellum, left post-central gyrus (post-CG), and left middle frontal gyrus (MFG)]. No regions were associated with the representation of letter case. This study showcases an investigational approach that allows for the differentiation of the neurotopography of the representational types that are key to our ability to produce written language.

Highlights

Producing written language requires the recruitment and intricate coordination of a number of processes and representations
Somewhat coarse-grained groupings of studies were used for this purpose, the analyses showed convergence across studies in terms of the association of the fusiform, inferior frontal gyrus (IFG), STG/STS, and some areas of superior and inferior parietal lobules (SPL)/inferior parietal lobule (IPL) with central components of spelling, while the superior frontal sulcus (SFS), pre-central gyrus (pre-CG), areas of IPL/SPL, and the right cerebellum were more closely associated with motor planning and programming in writing
For each of the letter-sensitive regions identified in Analysis 1, the beta values corresponding to the first 6 time points subsequent to the fourth stimulus on Change trials were used to compare the magnitude of the “release from inhibition” across the different Change conditions

Summary

Introduction

Producing written language requires the recruitment and intricate coordination of a number of processes and representations. THE PROCESSES AND REPRESENTATIONS OF WRITTEN SPELLING The spelling of familiar words is generally assumed to involve the retrieval from long-term memory (orthographic LTM) of the stored representations of word spellings that have been previously learned [for reviews see Roeltgen (1993); and Tainturier and Rapp (2000)]. In alphabetic languages, these lexical orthographic representations include information about letter identity and order, among other things (see Rapp and Fischer-Baum, in press). In addition to a possible role for a strictly visual representation of letter shape in writing [for discussion, see Menichelli et al (2008)] a number of motor-based representations have been proposed [see Rapp and Caramazza (1997), for a review]

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