Dare and Shillcock (2013) adapted the flankers task (Eriksen, 1995) to investigate orthographic processing and reading. Typically in this type of task, participants respond to central target words that are flanked on the left and right by stimuli that are irrelevant for the task. Target and flankers are presented together for a brief duration (typically 150–170 ms) and the flanking stimuli are related to targets on a given dimension, or unrelated to targets. Dare and Shillcock (2013) revealed effects of orthographic relatedness when the task is lexical decision (see also Grainger et al., 2014). For example, the target word ROCK is processed more quickly when flanked by its component letters such as in the sequence RO ROCK CK, compared with unrelated letters (e.g., PA ROCK TH). Crucially, this effect does not depend on the location of the overlapping letters (e.g., CK ROCK RO), hence prompting Grainger et al. (2014) to propose that orthographic information spanning the target and flankers is processed in parallel and integrated into a single processing channel for word identification (see Figure 3.4). Since the bigram representations in this model are themselves unordered (i.e., a bag‐of‐bigrams), the effect of related flanking bigrams (RO, CK) does not depend on their location.
Further work using word flankers has revealed that syntactic (Snell et al., 2017) and semantic (Snell, Declerck et al., 2018) information can be processed in parallel in multiword displays. This converges with evidence showing parallel word processing in both the Rapid Parallel Visual Presentation paradigm (Snell & Grainger, 2017) and the grammatical decision task (Mirault et al., 2018; Mirault & Grainger, 2020; see Snell & Grainger, 2019, for a summary of the evidence). Together, these findings have informed the development of a theoretical framework that both integrates word identification processes in an account of sentence‐level processing and specifies how different word identities can be simultaneously mapped onto distinct spatiotopic locations during reading, defined as locations within a line of text independent from where the eyes are fixating (Snell et al., 2017; Snell, van Leipsig, et al., 2018).
At a more general level of theorizing, it is possible to draw an interesting parallel between the letter‐word processing interface, the focus of the present chapter, and the word‐sentence interface. The key words that summarize the kind of processing involved at both interfaces are cascaded and interactive, as implemented in the interactive‐activation model (McClelland & Rumelhart, 1981; see Carreiras, Armstrong, Perea, & Frost, 2014, for a review of the evidence from neuroimaging studies, and Heilbron et al., 2020, for MEG evidence for interactivity). One can add a third key word, parallel processing, to the extent that letters in words are processed in parallel, and I would argue that, to a certain extent at least, the same is true for words in sentences.
Conclusions
This chapter opened with the argument that orthographic representations play a key role within the complex interplay of information processing that allows skilled readers to extract meaning from print. This argument hinges on two hypotheses. One is that words are the basic units of the reading process. The other is that letters are the basic units of words, and that orthographic processing is all about the processing of letter identities and letter‐order information. The review proceeded to consider the evidence in favor of letter‐based word recognition, and the evidence in favor of feature‐based letter identification as the starting point of the whole process as well as factors that are thought to determine variations in letter visibility when readers process multiletter arrays (acuity, crowding, and spatial attention). A description of some of the visual factors thought to determine ease of word identification, and most notably the position in a word where readers first fixate that word led to a consideration of how letter‐order information is encoded independently of where readers are looking at a word. Any viable mechanism for letter‐order encoding has to be able to accommodate a high degree of flexibility in this process, as evidenced by transposed‐letter effects, for example. The same type of flexibility was echoed in the section examining word‐in‐sentence processing, given the evidence for transposed‐word effects. Indeed, many of the phenomena observed at the letter‐word interface are paralleled at the word‐sentence interface, including parallel processing of letters in multiletter arrays and parallel processing of words in the multiword flankers task. This points to a common set of general‐purpose information‐processing principles that govern the overall process of reading. Exactly how such information‐processing principles adapt to the very special context of reading when children learn to read, and exactly how they are implemented in the literate brain, remain important questions for future research.
Acknowledgments
Much of the research reported in this chapter was made possible by funding from the European Research Council (ERC grants 230313 and 742141).
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