Semantic parafoveal processing in natural reading: Insight from fixation‐related potentials & eye movements

1 INTRODUCTION

One remarkable characteristic of reading is the large amount of information that we can extract from a text in an extremely brief period of time. However, there are limitations to how fast we can scan strings of words. During the presentation of linguistic and orthographic stimuli, an accurate description of the constraints of the visual system is necessary to fully understand the nature of subsequent cognitive operations. For instance, readers can process words located not only in the foveal visual field, but also in the parafoveal region –located between 1 and 5 degrees away from the fixation point. However, information in the parafoveal region is of poorer quality, due to decreased visual acuity and visual attention (Schotter et al., 2012). Therefore, the orthographic input will depend on the perception of letters at different spatial locations in combination with a series of sequential eye movements and attentional shifts. This leads us to some relevant questions: How many letters can we perceive in the parafoveal visual field? How deep do we process them? Is that information used only to guide our gaze or it is contributing to improve comprehension as well? At the core of all those issues is the debate on whether word meanings can be activated and integrated from parafoveal perception. In this study we have focused on parafoveal semantic processing during natural sentence reading combining two methodological approaches: The eye-tracking and the EEG-ERP research.

1.1 Semantic parafoveal processing: Evidence from eye tracking research

Eye movement research has investigated parafoveal processing using the gaze-contingent boundary paradigm (Rayner, 1975), which allows making inferences about how information obtained from parafoveal perception modulates subsequent reading behavior. In the boundary paradigm, an invisible boundary is located before a previewed word. When the reader’s gaze crosses the invisible boundary, the previewed word is replaced by a target word as the reader fixates it. Therefore, the previewed word could only have been perceived from the parafovea during the fixation of the previous word, and any difference in reading time of the target word when it is fixated must be due to that parafoveal processing (i.e., a parafoveal preview effect). The general conclusion from this paradigm is that readers regularly use orthographic and phonological features from parafoveal words, since fixated words need less time to be read after orthographically and phonologically related previews. On the other hand, evidence about the activation of semantic information was initially scarce (Hohenstein et al., 2010; Yan et al., 2009), leading to the conclusion that semantic information was not accessed parafoveally (Altarriba et al., 2001; Hyönä & Häikiö, 2005; Rayner et al., 1986; White et al., 2008; see Schotter et al., 2012).

Subsequent experiments have found that semantic information can be obtained from the parafovea (Rayner & Schotter, 2014; Schotter, 2013; Schotter et al., 2015), but they concluded that semantic preview effects are determined not by the relationship between the preview and target word, but rather by the semantic relationship between the parafoveal preview and the sentence context (i.e., plausibility preview effects; see Andrews & Veldre, 2019; Schotter, 2018). For example, Schotter and Jia (2016) used the boundary paradigm with identical, plausible and implausible unrelated previews (e.g., “Kevin’s brother ate all their fresh/baked/place bread in the apartment”), in addition to synonyms and antonyms (e.g., “Harry bought a broken watch/clock to repair for fun” and “Jane will travel north/south on her trip to Los Angeles next week” respectively); these words were read in low-constraint sentences, in order to ensure that predictability did not affect the processing of plausibility. They found that all plausible previews led to shorter durations compared to the implausible preview in first-pass reading measures on the target word, with no effects in later reading measures. Discrepancies between earlier and later eye movement reading measures could suggest that plausibility preview effects are short-lived; while implausible conditions had longer first-pass reading durations, total fixation durations were similar between plausible and implausible preview conditions (Schotter & Jia, 2016; Veldre & Andrews, 2016, 2017, 2018c). Andrews and Veldre (2019) suggested that a plausible preview may lead to later costs related to subsequent trans-saccadic integration processes between the preview and target words, which would lead to higher rates of regressions to the target word. This could explain the equivalence between plausible and implausible conditions in total fixation durations, since integrative processes of the preview with both the target word and the sentence context may influence this later processing measure. Since evidence suggest that plausibility preview effects are independent of trans-saccadic integration processes (Schotter & Leinenger, 2016; Veldre & Andrews, 2016; see Schotter, 2018), it is still possible that integrative processes of preview with the sentence context are still present in later processing after fixating the target word, but undetected by total fixation duration measures.

1.2 Semantic parafoveal processing: Evidence from ERPs and FRPs

While studying the time-course of processing may be limited in eye tracking research, EEG has proved particularly useful in this regard. Word recognition is a multimodal and cumulative process that extends along time, determined by many lexical and contextual factors (Barber & Kutas, 2007). Early EM measures are very sensitive to the computations that determine eye movement control. However, considering the characteristics and speed of natural reading, eye movement control uses only the minimum amount of information necessary to maximize the efficiency of saccades. Word processing is not finished after our gaze leaves a given word. It continues until meanings are fully processed and involves the continuous updating of mental representations. Language-related Event-Related Potential (ERP) components like the N400 peak much later (around 400 ms) than the average fixation duration (250 ms), and therefore are crucial physiological markers that may help us to understand the discrepancies between early and late EM measures. For instance, some cognitive processes may not be detected by early EM measures if they take place after saccades, but they may still modulate late ERP components and to have an impact on much later EM behavioral measures. Therefore, EEG and EM measures can be mutually complementary when describing the time course of parafoveal semantic processing during reading. Fixation-Related Potentials (FRPs) may be experimentally obtained through a co-registration set-up, allowing us to obtain ERPs time-locked to fixation onsets (similarly to EM fixation events) during natural sentence reading (Dimigen et al., 2011). By obtaining FRPs, semantic processing in the time-course of plausibility preview effects may be detected through the N400 amplitude modulation, which is an index of the ease of semantic access determined by sentence-level context information (Kutas & Federmeier, 2011).

Kretzschmar and colleagues (Kretzschmar et al., 2009) reported FRP effects compatible with parafoveal semantic processing in a natural reading task. They found modulations of the N400 component associated with semantically incongruent compared to congruent predictable words in highly constraining sentence constructions (e.g., “the opposite of black is white/yellow/nice”). These effects were found when Event-Related Potentials (ERPs) were time-locked to the last fixation before the target fixation, providing evidence that at least some semantic processing of the critical words took place parafoveally. However, considering the strong predictability manipulation used in that study, it is still an open question under which circumstances this kind of effect can be produced. In fact, a later study failed to replicate this parafoveal N400 effect in sentences with predictable targets but without extreme predictability (e.g., “The extremely skinny model looked like she suffered from anorexia and a lack of sleep”) when compared with unpredictable targets (see Kretzschmar et al., 2015). Consequently, it is important to note that, especially in high-constraint sentences, semantic effects derived from predictability manipulations can be confounded with sub-lexical processing, as predictability effects may extend to the level of orthography (see Laszlo & Federmeier, 2009) by shaping expectations of orthographic word forms (see Schuster et al., 2021).

The time course of parafoveal semantic processing during reading has been also addressed with artificial reading tasks that allow for tight experimental control; the presentation of words in the sentence is controlled via Rapid Serial Visual Presentation with bilateral flankers (Flanker-RSVP) while the reader fixates the word at the center of the screen, which is flanked to the right by the next word of the sentence and to the left by the previous word of the sentence (Barber et al., 2010, 2011, 2013; Li et al., 2015). For example, Barber et al. (2010) used this paradigm to manipulate the parafoveal word presented in the right flanker, which could be congruous or incongruous with the sentence context. Incongruent words in the parafoveally produced larger amplitudes in the N400 component time-locked to the presentation of the parafoveal word, showing that semantic processing of parafoveal words began before they were replaced by a new target word in the foveal region. In a later study, Barber et al. (2013) manipulated the contextual predictability of the critical words that were either congruent or incongruent within the sentential context. They again found larger N400 amplitudes for incongruent words when presented parafoveally while reading the previous word, both in high and low-constraint sentences. Interestingly, N400 modulations were greater under high contextual constraint, indicating that predictability can modulate the amount of parafoveal processing. In order to totally rule-out the possibility that predictions were primarily orthographic rather than semantic, Stites et al. (2017) used the same flanker-RSVP paradigm presenting a graded manipulation of the predictability of the target words, combining predictability and plausibility manipulations (high cloze probability, low cloze probability, unexpected but plausible, and anomalous words), which resulted in graded parafoveal N400 effects, with differences between unexpected plausible and anomalous words (i.e., a plausibility effect).

In spite of this evidence, it has not been established yet if the previously described ERP parafoveal semantic effects can be replicated under conditions of natural reading. In relation to this question, Barber et al. (2013; experiment 2) showed that parafoveal N400 effects in low constraint sentences were observed only at a slow stimulus presentation rate (SOA = 450 ms) but not when words were presented to a faster speed, similar to that of natural reading (SOA = 250 ms). Therefore, it seems that semantic N400 modulations related to predictability can interact with other sources of cognitive load to determine the amount of semantic parafoveal processing at any time (see also Payne et al., 2016). FRPs seem to be a natural step forward to tackle the ecological validity of parafoveal ERP findings in complex natural reading situations.

For instance, FRPs have already been useful in testing the ecological validity of parafoveal ERP and EM effects unrelated to semantic processing (e.g., Degno et al., 2019a, 2019b; Hutzler et al., 2013; Niefind & Dimigen, 2016; for a review, see Degno & Liversedge, 2020). Experimental conditions where previews and targets are visually different show greater processing costs when compared to conditions where previews and targets are identical, a preview effect related to display change frequently reported in EM research (see Schotter et al., 2012). The display change preview effect could be a mixture of preview benefits and preview costs (Kliegl et al., 2013). The mechanisms behind the greater preview costs of dissimilar previews may be affected by visual and attentional processes, for they can appear in the absence of conflicting orthography, phonology or semantics (Hutzler et al., 2013) and they can be increased by saliency (Hutzler et al., 2019). Therefore, these effects may be triggered by a perceptual mismatch that affects low level visuo-attentional processes, as well as by the identical preview facilitation of the subsequent target processing. These display change effects have also been reported in Flanker-RSVP-ERP paradigms during controlled reading (see Li et al., 2015), where valid previews elicited smaller N1 and N400 components than invalid preview when the target word was presented. More interestingly, in a situation more similar to natural reading, Dimigen et al. (2012) obtained FRPs while participants read word lists freely from left to right, and they used the boundary paradigm to manipulate parafoveal information. They presented an identical, semantically related or semantically unrelated word as a preview. They found that identical previews, compared to the other conditions where a display change was present, lead to facilitatory effects reflected in shorter fixation durations and a more positive amplitude that emerged from around 170 to 280 ms in the PO9 and PO10 electrodes. As they indicated, their findings in fixation durations and FRP amplitudes may support the idea that the display change effect is related to a pre-activation of orthographic codes before meaning activation. Additionally, they also reported a modulation of the N400 component such that the identical condition was less negative than the conditions with invalid previews. Dimigen et al. (2012) proposed that the N400 attenuation derived from a valid preview could be equivalent to the repetition priming effect described in other visual word recognition studies (see Holcomb & Grainger, 2006, 2007), which would suggest that similar mechanisms of trans-saccadic integration of low-level features in flanker paradigms could be involved in natural sentence reading.

The extraction of FRPs through a co-registration set-up provides some important advantages. For instance, both FRP and EM data together may discern between different types of processing that cause either distinct or comparable disruption to both data streams (for a review, see Degno & Liversedge, 2020). Additionally, FRPs have already been successfully combined with the boundary paradigm in word pair or word lists reading experiments exploring semantic parafoveal processing (Antúnez et al., 2021; Dimigen et al., 2012; López-Pérez et al., 2016). This combination allows a better interpretation of the ERP components that are highly overlapped in a situation of natural reading. Therefore, the ecological validity advantage of obtaining both FRPs and EM with the boundary paradigm over traditional ERP and EM approaches alone may provide a deeper understanding of how parafoveal processing may be affected by additional cognitive processes inherent to natural sentence reading, especially those related to reading speed and eye-movement control.

1.3 The present study

In this experiment, we analyzed the relationship between EM and FRP measures of semantic parafoveal processing in natural reading scenarios, posing two questions: (1) do ERP semantic parafoveal effects that have been obtained under controlled situations (e.g., Flanker-RSVP) replicate in a natural reading task? (2) Do these FRP-based plausibility preview effects provide clarity on the discrepancies in earlier and later EM measures? We recruited a sample of native English speakers and obtained FRPs through the co-registration of EM and EEG during a natural sentence-reading task. As in EM research, we used the boundary paradigm to manipulate the relationship of the previewed word with the sentence context. Participants read sentences such as “Harry bought a broken watch to repair for fun.” We manipulated the previewed word so that it was either identical to the target (e.g., Harry bought a broken watch…), an unrelated but plausible preview (e.g., Harry bought a broken chair…) or an unrelated and implausible preview (e.g., Harry bought a broken peace…; see Figure 1). The identical condition represented a situation where preview and target words share all features, allowing us to explore trans-saccadic integration effects when compared to the other two conditions where dissimilar previews may lead to preview costs. The comparison of plausible and implausible previews allowed us to explore integration processes of semantic preview information with the sentence context independent of any relationship between the preview and target because the previews in these conditions were both orthographically, phonologically, and semantically unrelated to the target word. The plausibility manipulation within low constraint sentences allowed us to confirm genuine parafoveal semantic processing in natural reading, ruling out alternative explanations such as orthographic prediction. Additionally, the comparison of the identical preview with the plausible and implausible previews was useful to separate out preview costs related to perceptual dissimilarity and to a mere pre-activation of orthographic codes before meaning activation. FRPs were time-locked to the pretarget and target words, in order to explore whether parafoveal information can be processed during the fixation of the pretarget word and if such semantic information may modulate the processing of the target word when fixated.

image

Illustration of the boundary paradigm. When readers crossed with their gaze an invisible boundary located between a pretarget (n) and a previewed word (n + 1), a target word replaced the preview word. The target word was always plausible to the sentence context. The previewed word could be identical to the target word (a), a different word but plausible to the sentence context (b) and a different word implausible to the sentence context (c)

We expected to replicate previous FRPs findings of preview effects related to a display change (Dimigen et al., 2012) in a more ecologically valid reading situation in early and later components of the FRP time-locked to the target word (e.g., N1 and N400). More importantly, considering previous electrophysiological evidence from controlled-reading paradigms where EMs were absent (Barber et al., 2013; Stites et al., 2017), we expected parafoveal word plausibility to modulate the N400 component time-locked to the fixation of the pretarget word (i.e., a greater negativity associated with the implausible preview). Such a finding would suggest that the N400 component involves semantic processing that is independent from EM behavior, as the effect would be found in both paradigms with and without the presence of eye movements, meaning that the semantic electrophysiological evidence is not disrupted or completely determined by the mechanisms related to eye movements. In addition to this, we expected plausibility preview effects in early reading measures on the target word and FRP components time-locked to fixation on the target word (i.e., around the 200 ms temporal window), consistent with previous EM evidence with similar experimental paradigms (Schotter & Jia, 2016; Veldre & Andrews, 2016, 2017, 2018c). Interestingly, and despite previous EM evidence showing that later reading measures are equivalent across plausible and implausible conditions, EEG measures (i.e., FRPs and the N400 component) may reveal types of processing undetected by fixation durations. Moreover, if plausibility effects are long-lasting, we would expect inconsistencies between EM and FRP measures, finding modulations in the N400 component for the FRPs time-locked to the target word, with total fixation durations not showing plausibility effects. This would be our main guess related to the later time-course of plausibility effects for semantic experimental manipulations may be less disrupting compared to purely visual preview manipulations to EM measures, leading to less consistency between both data streams (Degno & Liversedge, 2020). On the other hand, if plausibility effects are short-lived and absent in later processing, we would not find modulations in the N400 component. Such consistency between both data streams would suggest that EM and FRPs measures share common cognitive mechanisms related to semantic-plausibility parafoveal processing.

2 METHOD 2.1 Subjects

Fifty-nine Psychology students at University of South Florida (Florida, United States) volunteered to participate in the experiment in exchange for course credits. After excluding participants due to failure to follow instructions or stay awake (N = 5), problematic recording (e.g., inability to sufficiently reduce impedances in time or electrodes disconnected during recording; N = 6), and excessive data loss (i.e., subjects with fewer than 20 trials in any condition were excluded; N = 11), thirty-seven participants (21 females and 16 males, age: M = 20.7, SD = 4.19) were included in the analyses. They all were monolingual native English speakers, had normal or corrected vision, were right-handed and had no history of neurological disorders.

2.2 Materials and design

One hundred twenty-six sentences were taken from Schotter and Jia (2016) for the study. In each sentence, a preview of a specific target word could be either identical, an orthographically, phonologically, and semantically unrelated word that was plausible in the context of the sentence or an orthographically, phonologically, and semantically unrelated word that was implausible in the sentence context. All preview words shared the same length with the target word, were similar in lexical frequency, and had low orthographic similarity to the target word (for non-identical preview; see Table 1). Cloze probability norming was conducted with 30 volunteers who were not in the main experiment. This revealed that none of the preview words were predictable in the sentences (Table 1).

TABLE 1. Descriptive statistics of the target and preview words used in the experiment Condition Log10 freq Orthographic similarity with target word Cloze probability (%) M SD M SD M SD Plausible preview word 1.5 0.7 0.13 0.15 1.58 3.32 Implausible preview word 1.4 0.8 0.14 0.17 0 0 Identical preview word (Target word) 1.4 0.8 – – 2.93 2.89

In the original study, plausibility norms were collected for the entire sentence containing each of the preview/target words. For this study, we conducted an additional plausibility norming task, which included the sentence fragment only up to the preview word to confirm the plausibility manipulation at the point where the preview word was encountered (i.e., the point where the FRPs were time locked). For the norming study, 30 participants indicated if sentences were well or poorly written using a 1–7 Likert scale. Sentence conditions were counterbalanced and randomly presented. From the norming procedure, the average plausibility rating was 4.6 (SD = 0.98), 4.6 (SD = 0.9), and 2.9 (SD = 0.72), in the identical (target), plausible, and implausible conditions, respectively.

2.3 Task and procedure

Subjects were seated 60 cm away from a 20″ HP p1230 CRT monitor, with a refresh rate of 150 Hz and a screen resolution of 1024 × 768 pixels. After arriving, participants read and signed the informed consent. They were instructed to read sentences and to answer occasional yes-no comprehension questions. They answered the question by pressing the left or right button of a response controller, in order to answer affirmatively or negatively. After the EEG cap was set up and the eye tracker was calibrated, participants performed five practice trials before the real task, in order for them to get used to the experimental procedure.

During the task, a fixation point was presented in the center of the screen at the beginning of each trial in order to ensure that calibration of the eye tracker remained accurate. Then the experimenter started the trial, and a fixation box was presented on the left side of the screen, at the location of the beginning of the sentence. Once a fixation was detected in this box, the sentence was presented and stayed on the screen until the subject indicated that he had finished reading it by pressing a button on the response controller. They were also instructed to look at a target sticker located on the right side of the screen when they were done reading a sentence, to keep them from making additional eye movements that could have contaminated EM measures. When the reader’s gaze crossed an invisible boundary located between the pretarget (n) and the previewed word (n + 1), a target word replaced the preview word, following the boundary paradigm (Rayner, 1975; see Figure 1). A “yes-no” question was presented after 30 of the sentences (23.8%). Accuracy on comprehension questions was high in all subjects (M = 91.83%, SD = 4.49%). After the experiment, participants were asked if they noticed any display or word change and, in case they noticed any change, they were asked if they recognized any previewed word. Participants reported little to no display or word changes after the experiment (below 5 trials) and no one reported recognizing a previewed word when there was a display change.

Stimuli from this experiment were intermixed with 144 sentences and 40 comprehension questions from another experiment (see M. Antúnez, S. Milligan, J. A. Hernández-Cabrera, H. A. Barber, & E. R. Schotter, in prep). Following this experimental procedure, another reading task was performed and measures of spelling ability were collected. Those data were not analyzed for the purpose of this study and are not reported here. The entire experimental session took 90 min.

2.4 EEG and eye movements co-registration

EEG was recorded from 27 Ag/AgCl electrodes, following the 10/20 system (EasyCap, www.easycap.de). Four additional electrodes were placed in the external canthus of each eye and in the infra and supraorbital regions of the right eye. Electrodes were referenced online to the left mastoid and re-referenced offline to the algebraic mean of the right and left mastoids. The signal was amplified with a bandwidth of 0.01–100 Hz and a sampling rate of 500 Hz with the BrainVision system (www.brainproducts.com). Impedances were kept under 5 kΩ (electro-oculogram <10 kΩ).

EMs were recorded with a SR Research Ltd. Eyelink 1000 eye tracker in remote setup so that a target sticker was used to measure and control for head movements (Sampling rate = 500 Hz). Measures from the right eye were recorded, even though viewing was binocular. Calibration was performed on a standard five-point grid and eye position errors were less than 0.3° at each calibration point. Such calibration was performed not only at the beginning of the experiment but also during the task if calibration error was greater than 0.3°. Saccades crossing the invisible boundary activated the display change, which was completed almost immediately (M = 5.38 ms, SD = 0.39 ms).

2.5 Processing

EMs were processed and inspected through SR Research DataViewer. On the first stage of pre-processing, fixation that were preceded or followed by blinks were discarded. Additionally, trials where a display change was triggered prior to the eye movement to the target word were removed from later analysis (5.8% of total data). Fixations on the pretarget and target interest areas were considered and exported for the analyses of interest. Only trials where readers fixated both the pretarget and target words during first-pass reading were kept and fixation durations shorter than 50 ms and greater than 800 ms were excluded from analysis (retaining 82.14% of the total data trials).

The EEG data were pre-processed using the EEGLAB toolbox (Delorme & Makeig, 2004) for Matlab. The signal was filtered with a band-pass of 0.1–30 Hz and re-referenced offline to the average of the right and left mastoids. EMs were synchronized offline with the EEG signal with the EYE-EEG toolbox (Dimigen et al., 2011). Based on the trigger alignment, the mean synchronization error was below 1 ms. Independent components related to EMs were detected by using optimized ICA training data with overweighted spike potentials for better ocular artifact correction (Dimigen, 2020). Following Dimigen’s (2020) guidelines, ICA was trained on band-pass filtered training data (at a passband edge of 2.5 Hz) and ocular components were removed with eye tracker-guided component identification (Plöchl et al., 2012), with a variance ratio threshold of 1.1. EEG data were segmented into two epochs of interest: −200 to 800 ms time-locked to the first fixation on the pretarget (n) and target (n + 1) words. Non-ocular artifacts were detected with a moving window peak to peak threshold of 100 µV and later visually inspected and rejected manually, in order to control for possible artifacts not detected automatically. After processing both EM and EEG data streams, only participants with at least 20 trials per condition were kept in the analyses to maximize signal to noise ratio.

2.6 Analysis

For the EM data, we analyzed first fixation durations (duration of the first fixation made on a specific word during first-pass reading), single fixation durations (duration of the fixation made on a specific word, when there is only one fixation in first-pass reading), gaze durations (the sum of all fixations made on a specific word during first-pass reading before leaving it) and go-past time (the sum of all fixations on a specific word and subsequent fixations on words to the left of that word before fixating any word to the right of it) to assess early word processing. These measures were considered for both the pretarget (n) and target (n + 1) words, in order to study previous parafoveal processing and preview effects, respectively. Additionally, later word processing of the target word was assessed by analyzing total reading time (sum of all fixations on a word, including re-readings). Additionally, as in Schotter and Jia (2016), we analyzed fixation probability measures to better understand the effects of the preview word on the probability of fixating the target word during first-pass reading, the probability of making a regression out of the target word and re-reading words located to the left of it, and the probability of making a regression into the target word from later words in the sentence. All the chosen measures are standard reading measures for the study of the time-course of word processing (Rayner, 1998).

For the electrophysiological measures, FRPs time-locked to the pretarget (n) and target (n + 1) words were also considered to study both previous semantic parafoveal processing while fixating the pretarget word and semantic preview effects when fixating the target word. Theoretically we expected to analyze time windows related to the N400 component, which should hold significant effects, based on our hypothesis. A mass univariate analysis was performed to select the specific time windows. More precisely, a point-by-point t-test analysis using the Guthrie-Buchwald approach (Guthrie & Buchwald, 1991) was performed for the whole epoch. The beginning and end of a time window would be defined by the beginning and end of, at least, 12 consecutive points with a significant t-test (Guthrie & Buchwald, 1991).

Electrodes were grouped into three clustered factors in the final mixed model analyses, in order to estimate the topographic distribution of effects. We followed the same topographic design as Barber et al. (2013), with the anteriority, laterality and hemisphere factors. The anteriority factor had 5 levels: frontal (Fz, F7, F3, F4, F8), frontocentral (FC5, FC1, FC2, FC6), central (Cz, T7, C3, C4, T8), centroparietal (CP5, CP1, CP2, CP6), parietal (Pz, P7, P3, P4, P8). The laterality factor had 2 levels: medial (F3, F4, FC1, FC2, C3, C4, P3, P4, CP1, CP2), lateral (F7, F8, FC5, FC6, CP5, CP6, P7, P8, T7, T8). Finally, the hemisphere factor had 2 levels: left (F7, F3, FC5, FC1, T7, C3, CP5, CP1, P7, P3) and right (F8, F4, FC2, FC6, T8, C4, CP2, CP6, P8, P4).

In order to more accurately observe the display change effect in the FRP signal, an additional analysis was performed in parieto-occipital electrodes (P7, O1, O2, P8). We based our analysis on the FRP study of Dimigen et al. (2012), where he found a display change preview effect from 170 to 252 ms in PO9 and PO10 electrodes in free reading of lists of words. The temporal window of choice was guided by the point-by-point t-test analysis, although we expected the effect to be present at a similar time-window as in the mentioned study.

All analyses were performed with R software (http://www.rproject.org), by using the ULLRToolbox (https://sites.google.com/site/ullrtoolbox/home). All EM measures and mean voltage from the selected time windows were analyzed using linear mixed effects models with the lme4 and lmerTest R packages (Bates et al., 2011, 2015; Kunzetsova et al., 2017). If a preferable maximal random effects model (Barr et al., 2013) did not converge, we reduced the random effects structure to include random intercepts for subjects and items and a random slope for the preview condition for subjects, followed by random intercept for items and a random slope for subjects model. If none of these models converged, we reduced the structure to an only intercept for subjects and items random effects model. We used Satterthwaite’s method to calculate the pooled degrees of freedom of the variances (Khuri et al., 1998; Satterthwaite, 1941). In case of the non-normality of the residuals of the estimated models, a scaled power (box-cox) transformation was performed with the estimated lambda of the model (Box & Cox, 1964; Fox & Weisberg, 2018). For fixation probability measures, the mixed model was conducted using a logistic link function.

For the eye movements analysis, orthogonal Helmert contrast comparisons were included in the mixed model, which were decided a priori based on the hypothesis described in the introduction. We compared the identical preview condition to the combination of plausible and implausible preview conditions, in order to look for display change effects. Additionally, we compared plausible and implausible conditions to each other, in order to look for pure preview plausibility effects. For the FRP analysis, we included the three clustered topographic factors (5 × 2 × 2) to explore the interaction of the main manipulation with scalp topography. We used the anova output of lmer and emeans (Lenth et al., 2018) packages to look at the contrasts at relevant topographical levels. Contrasts were performed with the emeans package and p values were adjusted with Hochberg’s method (Hochberg, 1988). We report significant F and p values for the anova output for the topographical factors and b, t and p values of the fixed effects table.

3 RESULTS 3.1 Eye movements

For the EM analysis, we ran mixed models with random intercepts for items and subjects because the maximal model did not converge (Barr et al., 2013). Early reading time measures for fixation on the target words revealed that, compared to the implausible and plausible conditions, the identical condition led to shorter first fixation durations, single fixation durations, gaze durations, and go-past times (all ps < .001). Additionally, compared to the plausible condition, the implausible condition led to longer first fixation durations (p < .05), single fixation durations (p < .01), gaze durations (p < .01) and go-past times (p < .001). For fixations on the pretarget word, there were no differences in reading times between the different preview conditions.

Contrasts of total reading time spent on the target word revealed that the total time spent on the target word was shorter in the identical condition, compared to the conditions where a display change took place (p < .001). Contrary to earlier reading measures, time spent on the target word was longer for the plausible condition than for the implausible condition, but the difference was not significant (p = .38; see Figure 2).

image

Early (left) and late (right) reading measures on the target word for the identical, plausible and implausible conditions

Participants had similar target fixation probability across conditions (both ps > .05). However, participants regressed out of the target word more often in the implausible compared to the plausible preview condition (p < .01). Additionally, they regressed back to the target word more often in the plausible condition than in the implausible condition (p < .001), and less often when there was no display change compared to the other two conditions (p < .01; see Tables 2 and 3).

TABLE 2. Reading measures on the target word Measures Preview condition Identical Plausible Implausible First fixation duration 243.01 (2.73) 253.93 (2.68) 261.16 (2.73) Single fixation duration 243.67 (3.3) 252.92 (3.51) 263.35 (3.69) Gaze duration 262.5 (3.35) 277.87 (3.48) 288.4 (3.76) Go-past time 321.76 (6.79) 330.02 (7.22) 354.58 (6.25) Total time 379.29 (8.47) 417.64 (8.72) 400.09 (8.12) Fixation probability 0.88 (0.01) 0.90 (0.01) 0.90 (0.01) Regressions out of the target 0.12 (0.01) 0.11 (0.01) 0.14 (0.01) Regressions into the target 0.24 (0.01) 0.31 (0.01) 0.25 (0.01) Note Mean and standard errors. TABLE 3. Fixed effects of the contrasts of the linear mixed effects models for eye movements measures on the target word Measures Contrast b SE |t| p First fixation duration Identical versus Plausible + Implausible −5.220 1.066 −5.059 <.001 Plausible versus Implausible −3.028

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