Inhibition and facilitation in visual word recognition: Prefrontal contribution to the orthographic neighborhood size effect Christian J. Fiebach, a,b, ⁎ Brigitte Ricker, c Angela D. Friederici, b and Arthur M. Jacobs d a Departments of Psychology and Neurology, Ruprecht-Karls-Universität Heidelberg, Germany b Max Planck Institute for Human Cognitive and Brain Sciences, Leipzig, Germany c Department of Psychology, Catholic University Eichstätt, Germany d Department of Psychology, Experimental and Neurocognitive Group, Freie Universität Berlin, Germany Received 17 August 2006; revised 5 April 2007; accepted 6 April 2007 Available online 12 April 2007 The recognition of words is a central component of language processing. A major role for visual word recognition has been attributed to the orthographic neighbors of a word, i.e., words that are orthographically similar to a target word. It has been demonstrated that the presence of orthographic neighbors facilitates the recognition of words, but hinders the rejection of nonwords. It is therefore assumed that representations of orthographic neighbors are at least partially activated during word recognition, and that they influence word recognition depending on the specific task context. In the present study, we used fMRI to examine the neural bases of the effect of orthographic neighborhood size on speeded lexical decisions to words and nonwords. Our results demonstrate lexicality×neighborhood size interactions in mid-dorsolateral and medial prefrontal cortex, suggesting the involvement of a domain- general, extra-lexical process for orthographic neighborhood effects on word and nonword processing. This result challenges computational models that offer purely lexical accounts of the orthographic neighbor- hood effect and suggests an important role for executive control functions during visual word recognition. © 2007 Elsevier Inc. All rights reserved. Introduction The recognition of written words is a basic component of human language processes and of universal importance to modern everyday life. Recent investigations of the functional neuroanat- omy of visual word recognition indicate that accessing the representations of words stored in the mental lexicon primarily involves the temporal cortex of the left hemisphere. More specifically, it was suggested that basal occipitotemporal brain regions are involved in early processing stages of word recogni- tion, including the extraction of abstract word form representations from orthographic input (e.g., Cohen et al., 2000; Dehaene et al., 2002; Gaillard et al., 2006; McCandliss et al., 2003) (but see Price and Devlin, 2003, 2004) and the access to lexical representations (e.g., Beauregard et al., 1997; Bellgowan et al., 2003; Fiebach et al., 2002; Herbster et al., 1997; Howard et al., 1992; Kuo et al., 2003). Later stages of the word recognition process involve the activation of word meaning in lateral temporal cortex (e.g., Price, 2000). Functional neuroimaging studies often focused on the localiza- tion of visual word recognition processes, and made few or no assumptions concerning the specific sequence of processing steps involved. Thus, it is often assumed implicitly that lexical representations of words (i.e., a hypothetical mental lexicon) are sequentially searched through until a target word is identified. This assumption, however, appears unrealistic given that behavioral and computational evidence indicates that several lexical entries sharing orthographic features are initially activated during visual word processing (e.g., Grainger and Jacobs, 1996; McClelland and Rumelhart, 1981). Orthographic similarity has been operationa- lized as the subset of words that share all but one letter with a target word. This set of words is referred to as the ‘orthographic neighborhood’ of that target word (Coltheart et al., 1977). It is thus assumed that the representations of orthographic neighbors of a word are partially activated during the initial stages of word recognition, before lexical competition and lateral inhibition finally result in the identification of the correct lexical entry (e.g., Grainger and Jacobs, 1996). In a task such as lexical decision, the presence of a large neighborhood of orthographically similar words facilitates target word identification but makes it more difficult to classify letter strings as nonwords (e.g., Andrews, 1989; Carreiras et al., 1997; Forster and Shen, 1996; Sears et al., 1995). Interestingly, the facilitatory effect of neighborhood size on word recognition is task-dependent. Facilitatory effects of neighborhood www.elsevier.com/locate/ynimg NeuroImage 36 (2007) 901 – 911 ⁎ Corresponding author. Departments of Psychology and Neurology, Ruprecht-Karls-Universität Heidelberg, Hauptstr. 47-51, D-69117 Heidel- berg, Germany. E-mail address: fiebach@uni-heidelberg.de (C.J. Fiebach). Available online on ScienceDirect (www.sciencedirect.com). 1053-8119/$ - see front matter © 2007 Elsevier Inc. All rights reserved. doi:10.1016/j.neuroimage.2007.04.004