Readers Are Parallel Processors
Authors: Joshua Snell, Jonathan Grainger
Journal: Trends in Cognitive Sciences (2019)

Whether words are processed serially or in parallel continues to be a major debate in reading research. In the past decade, many researchers have embraced the seriality assumption.This Opinion article shows that empirical findings were incorrectly thought to falsify parallel processing and that the seriality assumption works only if one treats the word recognition process as a black box.The newest model of text reading comprises true word recognition mechanisms, causing it to spark fresh predictions. Successful tests of these predictions cannot be harmonized with serial processing.Reading research is ready for a paradigm shift, both methodologically (treading beyond the measurement of eye movements in sentence reading) and theoretically (abandoning serial processing in favor of parallel processing). Reading research has long endorsed the view that words are processed strictly one by one. The primary empirical test of this notion is the search for effects from upcoming words on readers' eye movements during sentence reading. Here we argue that no conclusions can be drawn from the absence of such effects, and that the serial versus parallel processing debate cannot be resolved without treading beyond the methodological scope of tracking eye movements. Recent considerations of how the brain organizes linguistic input have sparked key predictions in- and outside the realm of text reading, with ensuing research revealing phenomena that complicate the serial processing perspective. A case is made for parallelism, along with new methods to infer the cognitive architecture driving reading. Reading research has long endorsed the view that words are processed strictly one by one. The primary empirical test of this notion is the search for effects from upcoming words on readers' eye movements during sentence reading. Here we argue that no conclusions can be drawn from the absence of such effects, and that the serial versus parallel processing debate cannot be resolved without treading beyond the methodological scope of tracking eye movements. Recent considerations of how the brain organizes linguistic input have sparked key predictions in- and outside the realm of text reading, with ensuing research revealing phenomena that complicate the serial processing perspective. A case is made for parallelism, along with new methods to infer the cognitive architecture driving reading. It is evident that when we read, we adopt a largely serial strategy: texts are processed from left to right and from the top downwards, with the eyes' fixation jumping from one word to the next. Should we cease to impose seriality on the linguistic plane that bombards our retina with so many words at once, we would squander the canonical order of words and so a key ingredient of linguistic communication. Moreover, simultaneous processing of multiple words might conceivably incite word-to-word interference; for instance, through confusion about which letters belong to which word. For these reasons we can safely claim that during text reading we should ideally be able to confine our attention (see Glossary) to single words. But to what extent can we live up to this ideal? In the course towards a full understanding of the reading system, the question of whether readers process multiple words simultaneously has retained much prominence. Precisely a decade ago Reichle, Liversedge, Pollatsek, and Rayner expressed in this journal the opinion that parallel word processing is implausible [1.Reichle E. et al.Encoding multiple words simultaneously in reading is implausible.Trends Cogn. Sci. 2009; 13: 115-119Abstract Full Text Full Text PDF PubMed Scopus (114) Google Scholar]. At the time, it had already become clear that serial and parallel processing frameworks were equally capable of accounting for eye movement behavior during text reading [2.Reichle E. et al.Toward a model of eye movement control in reading.Psychol. Rev. 1998; 105: 125-157Crossref PubMed Scopus (928) Google Scholar, 3.Engbert R. et al.SWIFT: a dynamical model of saccade generation during reading.Psychol. Rev. 2005; 112: 777-813Crossref PubMed Scopus (765) Google Scholar, 4.Reilly R. Radach R. Some empirical tests of an interactive activation model of eye movement control in reading.Cogn. Syst. Res. 2006; 7: 34-55Crossref Scopus (209) Google Scholar]. Therefore, Reichle et al.'s argument for serial processing was not necessarily data driven (although later empirical work was deemed to be in support of serial processing; see the next section), but rather one of parsimony: a serial processing system recognizes words in the intended order and does not mix-up information across words, given that only one word is attended at any time. By contrast, a parallel processing system might recognize words out of order, and 'if one were to simultaneously activate orthographic units for two words, this would produce noisy output corresponding to neither word' ([1.Reichle E. et al.Encoding multiple words simultaneously in reading is implausible.Trends Cogn. Sci. 2009; 13: 115-119Abstract Full Text Full Text PDF PubMed Scopus (114) Google Scholar], see p. 117). A decade later, we can but agree that a serial processing system would have the simplest time reading, yet recent research has yielded various reasons to believe that the reading process is in fact not so simple. In this Opinion article we show that the serial processing assumption holds only if the word recognition process is treated as a black box – which has been a key aspect of both serial and parallel models of eye movements in text reading. The latest theoretical campaigns, marked by the implementation of word recognition mechanisms in models of text reading [5.Snell J. et al.OB1-reader: a model of word recognition and eye movements in text reading.Psychol. Rev. 2018; 125: 969-984Crossref PubMed Scopus (101) Google Scholar], have sparked new critical predictions, empirical tests of which are in support of parallel processing. Below, we first discuss why serial processing has been endorsed and show why some behavioral observations initially taken as strong evidence for serial processing may not be that. We subsequently discuss several phenomena predicted by the latest parallel processing framework and observed in ensuing experiments, that are difficult to reconcile with the seriality assumption. Taking these together, it appears sensible that readers are parallel processors and that paradigms beyond the realm of eye movements in sentence reading will shape the next trend of reading research. Whether the brain deals with language in a serial or parallel fashion has been debated across multiple domains of reading research (Box 1). With respect to eye movements in text reading, computational modeling has been one important endeavor. However, as serial and parallel processing models accounted for reading behavior equally well [2.Reichle E. et al.Toward a model of eye movement control in reading.Psychol. Rev. 1998; 105: 125-157Crossref PubMed Scopus (928) Google Scholar, 3.Engbert R. et al.SWIFT: a dynamical model of saccade generation during reading.Psychol. Rev. 2005; 112: 777-813Crossref PubMed Scopus (765) Google Scholar, 4.Reilly R. Radach R. Some empirical tests of an interactive activation model of eye movement control in reading.Cogn. Syst. Res. 2006; 7: 34-55Crossref Scopus (209) Google Scholar], it soon became clear that the debate could not be settled without empirical inquiry. Although divided by their premises, serial and parallel processing frameworks have in recent years been gauged on the basis of at least two shared rationales. The first of these is that if words were processed in parallel, the speed of recognizing a word should be influenced by the frequency of the following word. While some corpus studies have reported such effects [6.Kennedy A. Pynte J. Parafoveal-on-foveal effects in normal reading.Vis. Res. 2005; 45: 153-168Crossref PubMed Scopus (223) Google Scholar, 7.Kliegl R. et al.Tracking the mind during reading: the influence of past, present and future words on fixation durations.J. Exp. Psychol. Gen. 2006; 135: 12-35Crossref PubMed Scopus (416) Google Scholar], standard experimental designs have produced mixed results in this regard [8.Angele B. et al.Do successor effects in reading reflect lexical parafoveal processing? Evidence from corpus-based and experimental eye movement data.J. Mem. Lang. 2016; 88: 133-143Crossref Scopus (3) Google Scholar, 9.Brothers T. et al.Looking back on reading ahead: no evidence for lexical parafoveal-on-foveal effects.J. Mem. Lang. 2017; 96: 9-22Crossref Scopus (30) Google Scholar]. However, even from a parallel processing perspective it may be fairly logical that such effects are fleeting. Word recognition speed, insofar as it is determined by bottom-up processing of visual input, would mostly depend on the amount of processing resources allocated to each word in the visual field (i.e., the attentional distribution). There is no reason why this distribution should be modulated by word frequency (but see the next section, where we discuss the existence of indirect top-down effects of the upcoming word's frequency on word recognition speed).Box 1Various Editions of a 50-Year-Old DebateThroughout reading research's history, the serial versus parallel debate has continued to resurface in various forms addressing different levels of processing. Here are some examples from the past 50 years, and our opinion with respect to the status of these debates today.(1) Letter ProcessingThe beginning of contemporary research on single word reading pitted Forster's serial search model [46.Forster K. Accessing the mental lexicon.in: Wales R. Walker E. New Approaches to Language Mechanisms. 1976: 257-287Google Scholar] against Morton's parallel activation model [47.Morton J. Interaction of information in word recognition.Psychol. Rev. 1969; 76: 165-178Crossref Scopus (1479) Google Scholar]. These models contrasted both in the way letter identities were processed (left-to-right scan of letters versus parallel scanning), and in the way letter identities made contact with lexical representations (serial search vs parallel activation). A consensus has emerged in favor of parallel letter processing [48.Adelman J. et al.Letters in words are read simultaneously, not in left-to-right sequence.Psychol. Sci. 2010; 21: 1799-1801Crossref PubMed Scopus (65) Google Scholar, 49.Dehaene S. et al.The neural code for written words: a proposal.Trends Cogn. Sci. 2005; 9: 335-341Abstract Full Text Full Text PDF PubMed Scopus (774) Google Scholar] and the parallel activation of lexical representations [23.McClelland J. Rumelhart D. An interactive activation model of context effects in letter perception: part I. An account of basic findings.Psychol. Rev. 1981; 88: 375-407Crossref Scopus (3276) Google Scholar, 24.Whitney C. How the brain encodes the order of letters in a printed word: the SERIOL model and selective literature review.Psychon. Bull. Rev. 2001; 8: 221-243Crossref PubMed Scopus (455) Google Scholar, 25.Gomez P. et al.The Overlap Model: a model of letter position coding.Psychol. Rev. 2008; 115: 577-600Crossref PubMed Scopus (304) Google Scholar, 26.Davis C. The spatial coding model of visual word identification.Psychol. Rev. 2010; 117: 713-758Crossref PubMed Scopus (364) Google Scholar, 27.Grainger J. van Heuven W. Modeling letter position coding in printed word perception.in: Bonin P. The Mental Lexicon. Nova Science, 2003: 1-23Google Scholar, 28.Grainger J. Cracking the orthographic code: an introduction.Lang. Cogn. Proc. 2008; 23: 1-35Crossref Scopus (242) Google Scholar, 29.Carreiras M. et al.The what, when, where and how of visual word recognition.Trends Cogn. Sci. 2014; 18: 90-98Abstract Full Text Full Text PDF PubMed Scopus (227) Google Scholar].(2) Word ProcessingParallel processing of two simultaneously and briefly presented words was investigated in the early 1980s. Post-cued report of one of the words was sometimes contaminated by letter migrations from the other word, and this was taken as evidence for parallel processing of orthographic information across the two words [50.Mozer M. Letter migration in word perception.J. Exp. Psychol. Hum. Percept. Perform. 1983; 9: 531-546Crossref PubMed Scopus (127) Google Scholar, 51.McClelland J. Mozer M. Perceptual interactions in two-word displays: familiarity and similarity effects.J. Exp. Psychol. Hum. Percept. Perform. 1986; 12: 18-35Crossref PubMed Scopus (75) Google Scholar]. These results and conclusions nicely anticipated the more recent results discussed in the present Opinion article and provided confirmation of an earlier finding in favor of parallel processing of word identities in sentences [52.Jackson M. McClelland J. Sensory and cognitive determinants of reading speed.J. Verbal Learning Verbal Behav. 1975; 14: 565-574Crossref Scopus (46) Google Scholar].(3) Ambiguity ResolutionLanguage is rife with ambiguity, and its impact on linguistic processing has been investigated at multiple levels, with the same issue at stake: are different interpretations processed in parallel or is one processed before the other? At the single word level, the results of priming experiments suggest that readers entertain both meanings of homographs such as 'bank' (river/financial institution) and weigh them as a function of their relative frequency and any biasing context that might be present [53.Seidenberg M. et al.Automatic access of the meanings of ambiguous words in context: some limitations of knowledge-based processing.Cogn. Psychol. 1982; 14: 489-537Crossref Scopus (404) Google Scholar, 54.Burgess C. Simpson G. Cerebral hemispheric mechanisms in the retrieval of ambiguous word meanings.Brain Lang. 1988; 33: 86-103Crossref PubMed Scopus (319) Google Scholar]. At the sentence level, the classic serial 'garden path' model [55.Frazier L. Sentence processing: a tutorial review.in: Coltheart M. Attention and Performance. Lawrence Erlbaum Associates, 1987: 559-586Google Scholar] was challenged by the finding that ambiguity can sometimes facilitate processing [56.Traxler M. et al.Adjunct attachment is not a form of lexical ambiguity resolution.J. Mem. Lang. 1998; 39: 558-592Crossref Scopus (160) Google Scholar]. This finding provides support for parallel models of sentence parsing [57.Logačev P. Vasishth S. A multiple-channel model of task-dependent ambiguity resolution in sentence comprehension.Cogn. Sci. 2016; 40: 266-298Crossref PubMed Scopus (24) Google Scholar, 58.van Gompel R.P.G. et al.Unrestricted race: a new model of syntactic ambiguity resolution.in: Kennedy A. Reading as a Perceptual Process. Elsevier, 2000: 621-648Crossref Google Scholar] (see [59.Gibson E. Pearlmutter N. Distinguishing serial and parallel parsing.J. Psycholinguist. Res. 2000; 29: 231-240Crossref PubMed Scopus (45) Google Scholar] for further discussion and [60.MacDonald M. et al.Lexical nature of syntactic ambiguity resolution.Psychol. Rev. 1994; 101: 676-703Crossref PubMed Google Scholar, 61.Vosse T. Kempen G. Syntactic structure assembly in human parsing: a computational model based on competitive inhibition and a lexicalist grammar.Cognition. 2000; 75: 105-143Crossref PubMed Scopus (237) Google Scholar, 62.Levy R. Expectation-based syntactic comprehension.Cognition. 2008; 3: 1126-1177Crossref Scopus (1045) Google Scholar] for other parallel models). Throughout reading research's history, the serial versus parallel debate has continued to resurface in various forms addressing different levels of processing. Here are some examples from the past 50 years, and our opinion with respect to the status of these debates today. (1) Letter Processing The beginning of contemporary research on single word reading pitted Forster's serial search model [46.Forster K. Accessing the mental lexicon.in: Wales R. Walker E. New Approaches to Language Mechanisms. 1976: 257-287Google Scholar] against Morton's parallel activation model [47.Morton J. Interaction of information in word recognition.Psychol. Rev. 1969; 76: 165-178Crossref Scopus (1479) Google Scholar]. These models contrasted both in the way letter identities were processed (left-to-right scan of letters versus parallel scanning), and in the way letter identities made contact with lexical representations (serial search vs parallel activation). A consensus has emerged in favor of parallel letter processing [48.Adelman J. et al.Letters in words are read simultaneously, not in left-to-right sequence.Psychol. Sci. 2010; 21: 1799-1801Crossref PubMed Scopus (65) Google Scholar, 49.Dehaene S. et al.The neural code for written words: a proposal.Trends Cogn. Sci. 2005; 9: 335-341Abstract Full Text Full Text PDF PubMed Scopus (774) Google Scholar] and the parallel activation of lexical representations [23.McClelland J. Rumelhart D. An interactive activation model of context effects in letter perception: part I. An account of basic findings.Psychol. Rev. 1981; 88: 375-407Crossref Scopus (3276) Google Scholar, 24.Whitney C. How the brain encodes the order of letters in a printed word: the SERIOL model and selective literature review.Psychon. Bull. Rev. 2001; 8: 221-243Crossref PubMed Scopus (455) Google Scholar, 25.Gomez P. et al.The Overlap Model: a model of letter position coding.Psychol. Rev. 2008; 115: 577-600Crossref PubMed Scopus (304) Google Scholar, 26.Davis C. The spatial coding model of visual word identification.Psychol. Rev. 2010; 117: 713-758Crossref PubMed Scopus (364) Google Scholar, 27.Grainger J. van Heuven W. Modeling letter position coding in printed word perception.in: Bonin P. The Mental Lexicon. Nova Science, 2003: 1-23Google Scholar, 28.Grainger J. Cracking the orthographic code: an introduction.Lang. Cogn. Proc. 2008; 23: 1-35Crossref Scopus (242) Google Scholar, 29.Carreiras M. et al.The what, when, where and how of visual word recognition.Trends Cogn. Sci. 2014; 18: 90-98Abstract Full Text Full Text PDF PubMed Scopus (227) Google Scholar]. (2) Word Processing Parallel processing of two simultaneously and briefly presented words was investigated in the early 1980s. Post-cued report of one of the words was sometimes contaminated by letter migrations from the other word, and this was taken as evidence for parallel processing of orthographic information across the two words [50.Mozer M. Letter migration in word perception.J. Exp. Psychol. Hum. Percept. Perform. 1983; 9: 531-546Crossref PubMed Scopus (127) Google Scholar, 51.McClelland J. Mozer M. Perceptual interactions in two-word displays: familiarity and similarity effects.J. Exp. Psychol. Hum. Percept. Perform. 1986; 12: 18-35Crossref PubMed Scopus (75) Google Scholar]. These results and conclusions nicely anticipated the more recent results discussed in the present Opinion article and provided confirmation of an earlier finding in favor of parallel processing of word identities in sentences [52.Jackson M. McClelland J. Sensory and cognitive determinants of reading speed.J. Verbal Learning Verbal Behav. 1975; 14: 565-574Crossref Scopus (46) Google Scholar]. (3) Ambiguity Resolution Language is rife with ambiguity, and its impact on linguistic processing has been investigated at multiple levels, with the same issue at stake: are different interpretations processed in parallel or is one processed before the other? At the single word level, the results of priming experiments suggest that readers entertain both meanings of homographs such as 'bank' (river/financial institution) and weigh them as a function of their relative frequency and any biasing context that might be present [53.Seidenberg M. et al.Automatic access of the meanings of ambiguous words in context: some limitations of knowledge-based processing.Cogn. Psychol. 1982; 14: 489-537Crossref Scopus (404) Google Scholar, 54.Burgess C. Simpson G. Cerebral hemispheric mechanisms in the retrieval of ambiguous word meanings.Brain Lang. 1988; 33: 86-103Crossref PubMed Scopus (319) Google Scholar]. At the sentence level, the classic serial 'garden path' model [55.Frazier L. Sentence processing: a tutorial review.in: Coltheart M. Attention and Performance. Lawrence Erlbaum Associates, 1987: 559-586Google Scholar] was challenged by the finding that ambiguity can sometimes facilitate processing [56.Traxler M. et al.Adjunct attachment is not a form of lexical ambiguity resolution.J. Mem. Lang. 1998; 39: 558-592Crossref Scopus (160) Google Scholar]. This finding provides support for parallel models of sentence parsing [57.Logačev P. Vasishth S. A multiple-channel model of task-dependent ambiguity resolution in sentence comprehension.Cogn. Sci. 2016; 40: 266-298Crossref PubMed Scopus (24) Google Scholar, 58.van Gompel R.P.G. et al.Unrestricted race: a new model of syntactic ambiguity resolution.in: Kennedy A. Reading as a Perceptual Process. Elsevier, 2000: 621-648Crossref Google Scholar] (see [59.Gibson E. Pearlmutter N. Distinguishing serial and parallel parsing.J. Psycholinguist. Res. 2000; 29: 231-240Crossref PubMed Scopus (45) Google Scholar] for further discussion and [60.MacDonald M. et al.Lexical nature of syntactic ambiguity resolution.Psychol. Rev. 1994; 101: 676-703Crossref PubMed Google Scholar, 61.Vosse T. Kempen G. Syntactic structure assembly in human parsing: a computational model based on competitive inhibition and a lexicalist grammar.Cognition. 2000; 75: 105-143Crossref PubMed Scopus (237) Google Scholar, 62.Levy R. Expectation-based syntactic comprehension.Cognition. 2008; 3: 1126-1177Crossref Scopus (1045) Google Scholar] for other parallel models). The second assumption has been that if words are processed in parallel, information should be spatially integrated across words, such that readers will more rapidly recognize certain word characteristics (e.g., letters, sounds, meaning) if those characteristics are shared with surrounding words [10.Inhoff A. et al.Allocation of visuospatial attention and saccade programming during reading.in: Kennedy A. Reading as a Perceptual Process. Elsevier, 2000Crossref Google Scholar, 11.Dare N. Shillcock R. Serial and parallel processing in reading: investigating the effects of parafoveal orthographic information on nonisolated word recognition.Q. J. Exp. Psychol. 2013; 66: 417-428Crossref Scopus (40) Google Scholar, 12.Angele B. et al.Parafoveal–foveal overlap can facilitate ongoing word identification during reading: evidence from eye movements.J. Exp. Psychol. Hum. Percep. Perform. 2013; 39: 526-538Crossref PubMed Scopus (43) Google Scholar, 13.Snell J. et al.Integration of parafoveal orthographic information during foveal word reading: beyond the sub-lexical level?.Q. J. Exp. Psychol. 2017; 70: 1984-1996Crossref Scopus (31) Google Scholar, 14.Snell J. et al.Evidence for simultaneous syntactic processing of multiple words in reading.PLoS One. 2017; 12e0173720Crossref PubMed Scopus (56) Google Scholar, 15.Snell J. et al.Parallel semantic processing in reading revisited: effects of translation equivalents in bilingual readers.Lang. Cogn. Neurosci. 2018; 33: 563-574Crossref Scopus (32) Google Scholar]. As it turns out, readers do integrate letter information across words [10.Inhoff A. et al.Allocation of visuospatial attention and saccade programming during reading.in: Kennedy A. Reading as a Perceptual Process. Elsevier, 2000Crossref Google Scholar, 11.Dare N. Shillcock R. Serial and parallel processing in reading: investigating the effects of parafoveal orthographic information on nonisolated word recognition.Q. J. Exp. Psychol. 2013; 66: 417-428Crossref Scopus (40) Google Scholar, 12.Angele B. et al.Parafoveal–foveal overlap can facilitate ongoing word identification during reading: evidence from eye movements.J. Exp. Psychol. Hum. Percep. Perform. 2013; 39: 526-538Crossref PubMed Scopus (43) Google Scholar, 13.Snell J. et al.Integration of parafoveal orthographic information during foveal word reading: beyond the sub-lexical level?.Q. J. Exp. Psychol. 2017; 70: 1984-1996Crossref Scopus (31) Google Scholar, 14.Snell J. et al.Evidence for simultaneous syntactic processing of multiple words in reading.PLoS One. 2017; 12e0173720Crossref PubMed Scopus (56) Google Scholar, 15.Snell J. et al.Parallel semantic processing in reading revisited: effects of translation equivalents in bilingual readers.Lang. Cogn. Neurosci. 2018; 33: 563-574Crossref Scopus (32) Google Scholar], but higher-level integration effects (e.g., the word 'dog' being recognized faster when followed by 'cat' than when followed by an unrelated word) have remained largely elusive [12.Angele B. et al.Parafoveal–foveal overlap can facilitate ongoing word identification during reading: evidence from eye movements.J. Exp. Psychol. Hum. Percep. Perform. 2013; 39: 526-538Crossref PubMed Scopus (43) Google Scholar, 13.Snell J. et al.Integration of parafoveal orthographic information during foveal word reading: beyond the sub-lexical level?.Q. J. Exp. Psychol. 2017; 70: 1984-1996Crossref Scopus (31) Google Scholar, 14.Snell J. et al.Evidence for simultaneous syntactic processing of multiple words in reading.PLoS One. 2017; 12e0173720Crossref PubMed Scopus (56) Google Scholar, 15.Snell J. et al.Parallel semantic processing in reading revisited: effects of translation equivalents in bilingual readers.Lang. Cogn. Neurosci. 2018; 33: 563-574Crossref Scopus (32) Google Scholar]. This has led researchers to believe that parallel processing may occur at sublexical levels, but that lexical access nonetheless occurs serially. But this conclusion is not warranted. Parallel processing may well proceed without integrating high-level information across words [5.Snell J. et al.OB1-reader: a model of word recognition and eye movements in text reading.Psychol. Rev. 2018; 125: 969-984Crossref PubMed Scopus (101) Google Scholar, 14.Snell J. et al.Evidence for simultaneous syntactic processing of multiple words in reading.PLoS One. 2017; 12e0173720Crossref PubMed Scopus (56) Google Scholar, 15.Snell J. et al.Parallel semantic processing in reading revisited: effects of translation equivalents in bilingual readers.Lang. Cogn. Neurosci. 2018; 33: 563-574Crossref Scopus (32) Google Scholar]. The rationale for this alternative scenario is simple: readers would have to be able to keep track of which meanings belong to which positions in the sequence, given that each word has a unique role in contributing to sentence comprehension. A parallel processing system would be fundamentally flawed if it allowed cross-word leakage of high-level information (for an explanation of why letter information is nonetheless integrated across words, see Box 2). In neurophysiological terms, inherent to parallel processing must be a lack of lateral connections among the neural nodes representing semantic concepts activated by different words in the sentence.Box 2Lessons from Research on Parafoveal ProcessingAs most words are big enough to occupy the whole region of sharp, central vision (the fovea), parallel word processing would necessitate some words to be processed in surrounding regions of the visual field, the parafovea. Therefore, an important question has been to what extent parafoveal words are processed at all. This has been investigated with the gaze-contingent boundary paradigm [63.Rayner K. The perceptual span and peripheral cues in reading.Cogn. Psychol. 1975; 7: 65-81Crossref Scopus (781) Google Scholar], whereby display manipulations prevent target word visibility until the eyes move to the target's location; (note, however, that some studies have shown that readers sometimes binocularly foveate two words simultaneously [64.Shillcock R. et al.Binocular foveation in reading.Atten. Percept. Psychophys. 2010; 72: 2184-2203Crossref PubMed Scopus (12) Google Scholar], which should arguably bode chaos for a serial processing system). A consistent finding is that denying parafoveal preview leads to prolonged target viewing times [65.Briihl D. Inhoff A. Integrating information across fixations during reading.J. Exp. Psychol. Learn. Mem. Cogn. 1995; 21: 55-67Crossref Scopus (84) Google Scholar, 66.Kliegl R. et al.Preview benefit and parafoveal-on-foveal effects from word n+2.J. Exp. Psychol. Hum. Percept. Perform. 2007; 33: 1250-1255Crossref PubMed Scopus (90) Google Scholar, 67.Inhoff A.W. Rayner K. Parafoveal word perception: a case against semantic preprocessing.Percept. Psychophys. 1980; 27: 457-464Crossref PubMed Scopus (45) Google Scholar]. Consequently there has long been consensus that sublexical (letter) processing occurs for upcoming words. Higher-level (e.g., semantic, syntactic) preview was long considered controversial [68.Rayner K. et al.Lack of semantic parafoveal preview revisited.Psychon. Bull. Rev. 2014; 21: 1067-1072Crossref PubMed Scopus (47) Google Scholar, 69.Hohenstein S. Kliegl R. Semantic preview benefit during reading.J. Exp. Psychol. Learn. Mem. 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