Getting ahead of yourself: Parafoveal word expectancy modulates the N400 during sentence reading

Abstract

An important question in the reading literature regards the nature of the semantic information readers can extract from the parafovea (i.e., the next word in a sentence). Recent eye-tracking findings have found a semantic parafoveal preview benefit under many circumstances, and findings from event-related brain potentials (ERPs) also suggest that readers can at least detect semantic anomalies parafoveally (Barber, Van der Meij, & Kutas, Psychophysiology, 50(1), 48-59, 2013). We use ERPs to ask whether fine-grained aspects of semantic expectancy can affect the N400 elicited by a word appearing in the parafovea. In an RSVP-with-flankers paradigm, sentences were presented word by word, flanked 2° bilaterally by the previous and upcoming words. Stimuli consisted of high constraint sentences that were identical up to the target word, which could be expected, unexpected but plausible, or anomalous, as well as low constraint sentences that were always completed with the most expected ending. Findings revealed an N400 effect to the target word when it appeared in the parafovea, which was graded with respect to the target's expectancy and congruency within the sentence context. Furthermore, when targets appeared at central fixation, this graded congruency effect was mitigated, suggesting that the semantic information gleaned from parafoveal vision functionally changes the semantic processing of those words when foveated.

Keywords: ERPs; Lexical access; Parafoveal processing; Semantics.

Fig. 1

Diagrams depicting the structure of a single trial. a) Sentences were presented serially in triads, with the target word appearing in center of screen (Note: Interword spacing is not drawn to scale). Triads were visible for 100 ms, with a 350 ms interstimulus interval. b) The current word of the sentence was presented centrally, and each flanker word started 2° of visual angle from central fixation. c) The first set of analyses considers trials on which the target word appears in the parafovea, with the pre-target word at central fixation. On the next triad, which appeared 450 ms after the onset of the previous triad, the target word moved to central fixation, and a neutral post-target word appeared in the parafovea

Fig. 2

Grand-average ERPs at all 26 electrode sites for the parafoveal N400 congruency effect. The N400 effect is graded by parafoveal word expectancy, being the most negative for anomalous words and the most facilitated for the expected words with the highest cloze probability. The figure inset depicts the grand average ERP amplitude of the bipolar horizontal eye channel. Deflections of roughly 16 μV are associated with saccades of 1° of visual angle. There was very little activity in this channel, especially during the first 100 ms of processing (the duration that the stimuli were visible on the screen), suggesting that participants consistently maintained central fixation

Fig. 3

Grand-average ERPs at all 26 electrode sites for the foveal N400 congruency effect (presented from 100 ms prior to the target word appearing the in fovea). N400 expectancy effect is drastically reduced when target words appear in the parafovea, with only a numeric difference in N400 amplitude across these conditions

Fig. 4

a) Grand-average ERPs at the middle central electrode comparing the parafoveal N400 congruency effect (left panel) and foveal N400 congruency effect (right panel). Note that negative is plotted up. The same baseline period was used for both measurements: 100 ms prestimulus onset of the target-in-parafovea. As such, the foveal effect is simply plotted starting from the onset of the target word in the fovea, which occurred at 450 ms after the time-locking point (i.e., 450 ms after the target appeared in the parafovea, in the middle of the N400 to the parafoveal word). b) Plot of individual item-level N400 amplitude by cloze probability, overlaid with the slope of the cloze effect for the parafoveal N400 (red) and foveal N400 effect (blue). Note that negative is plotted up, for ease of comparison with the ERP plot in a. The steeper slope for the parafoveal effect indicates that parafoveal N400 amplitudes were graded with respect to cloze probability, whereas the flatter slope of the foveal N400 effect shows that this effect was largely eliminated in foveal processing