Revisiting the incremental effects of context on word processing: Evidence from single-word event-related brain potentials

Abstract

The amplitude of the N400-an event-related potential (ERP) component linked to meaning processing and initial access to semantic memory-is inversely related to the incremental buildup of semantic context over the course of a sentence. We revisited the nature and scope of this incremental context effect, adopting a word-level linear mixed-effects modeling approach, with the goal of probing the continuous and incremental effects of semantic and syntactic context on multiple aspects of lexical processing during sentence comprehension (i.e., effects of word frequency and orthographic neighborhood). First, we replicated the classic word-position effect at the single-word level: Open-class words showed reductions in N400 amplitude with increasing word position in semantically congruent sentences only. Importantly, we found that accruing sentence context had separable influences on the effects of frequency and neighborhood on the N400. Word frequency effects were reduced with accumulating semantic context. However, orthographic neighborhood was unaffected by accumulating context, showing robust effects on the N400 across all words, even within congruent sentences. Additionally, we found that N400 amplitudes to closed-class words were reduced with incrementally constraining syntactic context in sentences that provided only syntactic constraints. Taken together, our findings indicate that modeling word-level variability in ERPs reveals mechanisms by which different sources of information simultaneously contribute to the unfolding neural dynamics of comprehension.

Keywords: Event-related potentials (ERPs); Lexical processing; Linear mixed-effects model; N400; Sentence comprehension.

Figure 1

a. Linear word position effects on single-word ERPs to open-class words in the N400 epoch (300-500 ms) plotted separately for each sentence context. Error bars reflect the between-subject standard error of the mean computed across all subjects, words, and channels at each word position. b. Grand-average ERPs illustrating word position effects for open-class words in congruent sentences. Two-word bins are presented, color-coded by word position, over six central parietal electrodes. Negative is plotted up. c. Scalp topography of the best linear unbiased estimates of word position effects on N400 amplitude for open-class words in congruent sentences (see text for details). Electrode channel sites with grey circles are those for which data was included in the single-word mixed-effect models.

Figure 2

Fixed-effect parameter estimates and corresponding 95% profile confidence intervals from Model 2. Note: Estimates with intervals containing 0 (grey circles) do not meet traditional levels of statistical significance.

Figure 3

a. Model estimated partial-effects plots of the Frequency × Word Position × Context interaction. b. Model estimated partial-effects plots of the Orthographic Neighborhood × Word Position × Context interaction.

Figure 4

a. Linear word position effects on single-word ERPs to closed-class words in the N400 epoch (300-500 ms) plotted separately for each sentence context. Error bars reflect the between-subject standard error of the mean computed across all subjects, words, and channels. b. Grand-average ERPs illustrating word position effects for closed-class words in syntactic prose. Two-word bins are presented, color-coded by word position, over six central parietal electrodes. Negative is plotted up. c. Scalp topography of the best linear unbiased estimates of word position effects on N400 amplitude for closed-class words in syntactic prose (see text for details). Electrode channel sites with grey circles are those for which data was included in the single-word mixed-effect models.