Dissociating parafoveal preview benefit and parafovea-on-fovea effects during reading: A combined eye tracking and EEG study.

During reading, the parafoveal processing of an upcoming word n+1 can influence word recognition in two ways: It can affect fixation behavior during the preceding fixation on word n (parafovea-on-fovea effect, POF), and it can facilitate subsequent foveal processing once word n+1 is fixated (preview benefit). While preview benefits are established, evidence for POF effects is mixed. Recently, it has been suggested that POF effects exist, but have a delayed impact on saccade planning and thus coincide with preview benefits measured on word n+1. We combined eye movement and EEG recordings to investigate and separate neural correlates of POF and preview benefit effects. Participants read lists of nouns either in a boundary paradigm or the RSVP-with-flankers paradigm, while we recorded fixation- or event-related potentials (FRPs/ERPs), respectively. The validity and lexical frequency of the word shown as preview for the upcoming word n+1 were orthogonally manipulated. Analyses focused on the first fixation on word n+1. Preview validity (correct vs. incorrect preview) strongly modulated fixation times and electrophysiological N1 amplitudes, replicating previous findings. Importantly, gaze durations and FRPs measured on word n+1 were also affected by the frequency of the word shown as preview, with low-frequency previews eliciting a sustained, N400-like centroparietal negativity. Results support the idea that POF effects exist but affect word recognition with a delay. Lastly, once word n+1 was fixated, its frequency also modulated N1 amplitudes in ERPs and FRPs. Taken together, we separated immediate and delayed effects of parafoveal processing on brain correlates of word recognition.

Neural Correlates of Word Recognition: A Systematic Comparison of Natural Reading and Rapid Serial Visual Presentation.

Neural correlates of word recognition are commonly studied with (rapid) serial visual presentation (RSVP), a condition that eliminates three fundamental properties of natural reading: parafoveal preprocessing, saccade execution, and the fast changes in attentional processing load occurring from fixation to fixation. We combined eye-tracking and EEG to systematically investigate the impact of all three factors on brain-electric activity during reading. Participants read lists of words either actively with eye movements (eliciting fixation-related potentials) or maintained fixation while the text moved passively through foveal vision at a matched pace (RSVP-with-flankers paradigm, eliciting ERPs). The preview of the upcoming word was manipulated by changing the number of parafoveally visible letters. Processing load was varied by presenting words of varying lexical frequency. We found that all three factors have strong interactive effects on the brain's responses to words: Once a word was fixated, occipitotemporal N1 amplitude decreased monotonically with the amount of parafoveal information available during the preceding fixation; hence, the N1 component was markedly attenuated under reading conditions with preview. Importantly, this preview effect was substantially larger during active reading (with saccades) than during passive RSVP with flankers, suggesting that the execution of eye movements facilitates word recognition by increasing parafoveal preprocessing. Lastly, we found that the N1 component elicited by a word also reflects the lexical processing load imposed by the previously inspected word. Together, these results demonstrate that, under more natural conditions, words are recognized in a spatiotemporally distributed and interdependent manner across multiple eye fixations, a process that is mediated by active motor behavior.

Parafoveal processing in reading Chinese sentences: Evidence from event-related brain potentials.

Natural reading involves the preprocessing of upcoming words, resulting in shorter fixations on words visible in the parafovea during preceding fixations. While this preview benefit is established in behavior, its brain-electric correlates have only recently been investigated. Using fixation-related potentials, an attenuation of the occipitotemporal N1 component for words that were parafoveally visible during preceding fixations has been demonstrated. In contrast, another study, using an RSVP paradigm with parafoveal flanker words, observed no such general preview benefit in ERPs, but instead reported N400 effects triggered by semantically incongruous parafoveal words. To follow up on these discrepant findings and to extend them to a nonalphabetic writing system, we conducted two ERP experiments with Chinese readers using the RSVP-with-flankers paradigm and rigorous fixation control via eye tracking. We replicate robust parafoveal N400 semantic congruency effects in Chinese participants. Additionally, we found that, once a word was directly looked at, words after a valid preview elicited a smaller N1 and a weaker N400 than those after an invalid preview. Results underline the importance of considering parafoveal vision in ERP studies on reading.

Are individual differences in reading speed related to extrafoveal visual acuity and crowding?

Readers differ considerably in their speed of self-paced reading. One factor known to influence fixation durations in reading is the preprocessing of words in parafoveal vision. Here we investigated whether individual differences in reading speed or the amount of information extracted from upcoming words (the preview benefit) can be explained by basic differences in extrafoveal vision--i.e., the ability to recognize peripheral letters with or without the presence of flanking letters. Forty participants were given an adaptive test to determine their eccentricity thresholds for the identification of letters presented either in isolation (extrafoveal acuity) or flanked by other letters (crowded letter recognition). In a separate eye-tracking experiment, the same participants read lists of words from left to right, while the preview of the upcoming words was manipulated with the gaze-contingent moving window technique. Relationships between dependent measures were analyzed on the observational level and with linear mixed models. We obtained highly reliable estimates both for extrafoveal letter identification (acuity and crowding) and measures of reading speed (overall reading speed, size of preview benefit). Reading speed was higher in participants with larger uncrowded windows. However, the strength of this relationship was moderate and it was only observed if other sources of variance in reading speed (e.g., the occurrence of regressive saccades) were eliminated. Moreover, the size of the preview benefit--an important factor in normal reading--was larger in participants with better extrafoveal acuity. Together, these results indicate a significant albeit moderate contribution of extrafoveal vision to individual differences in reading speed.