A model-guided dissociation between subcortical and cortical contributions to word recognition

Florian Hutzler,Arthur M Jacobs,Martin Kronbichler,Mario Braun,Fabio Richlan,Stefan Hawelka

doi:10.1038/s41598-019-41011-9

Abstract

Neurocognitive studies of visual word recognition have provided information about brain activity correlated with orthographic processing. Some of these studies related the orthographic neighborhood density of letter strings to the amount of hypothetical global lexical activity (GLA) in the brain as simulated by computational models of word recognition. To further investigate this issue, we used GLA of words and nonwords from the multiple read-out model of visual word recognition (MROM) and related this activity to neural correlates of orthographic processing in the brain by using functional magnetic resonance imaging (fMRI). Words and nonwords elicited linear effects in the cortex with increasing BOLD responses for decreasing values of GLA. In addition, words showed increasing linear BOLD responses for increasing GLA values in subcortical regions comprising the hippocampus, globus pallidus and caudate nucleus. We propose that these regions are involved in the matching of orthographic input onto representations in long-term memory. The results speak to a potential involvement of the basal ganglia in visual word recognition with globus pallidus and caudate nucleus activity potentially reflecting maintenance of orthographic input in working memory supporting the matching of the input onto stored representations by selection of appropriate lexical candidates and the inhibition of orthographically similar but non-matching candidates.

Highlights

Successful processing of written words requires the activation and retrieval/reconstruction of stored orthographic information about these words from memory
In studies of visual word recognition orthographic similarity is typically operationalized by neighborhood density
To identify regions related to orthographic similarity we looked for effects of global lexical activity (GLA) by contrasting the highest vs. lowest levels of GLA, separately for words and nonwords

Summary

Introduction

Successful processing of written words requires the activation and retrieval/reconstruction of stored orthographic information about these words from memory. When processing words with a high number of neighbors it is assumed – as shown by computer simulations – that these generate high GLA values in the hypothetical mental lexicon through partial activation of all similar representation units[5]. This extra activity is supposed to allow for the fast-guess resulting in shorter ‘yes’ responses compared to words with only some neighbors and low values of GLA. As GLA was previously shown to correlate with reaction times[6,7] and to correlate with a number of linguistic measures like neighborhood density, word frequency, bigram frequency etc. (see Methods), we use GLA as a single computational measure of orthographic familiarity

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