Time for prediction? The effect of presentation rate on predictive sentence comprehension during word-by-word reading

Abstract

Predictive processing is a core component of normal language comprehension, but the brain may not engage in prediction to the same extent in all circumstances. This study investigates the effects of timing on anticipatory comprehension mechanisms. Event-related brain potentials (ERPs) were recorded while participants read two-sentence mini-scenarios previously shown to elicit prediction-related effects for implausible items that are categorically related to expected items ('They wanted to make the hotel look more like a tropical resort. So along the driveway they planted rows of PALMS/PINES/TULIPS.'). The first sentence of every pair was presented in its entirety and was self-paced. The second sentence was presented word-by-word with a fixed stimulus onset asynchrony (SOA) of either 500 msec or 250 msec that was manipulated in a within-subjects blocked design. Amplitudes of the N400 ERP component are taken as a neural index of demands on semantic processing. At 500 msec SOA, implausible words related to predictable words elicited reduced N400 amplitudes compared to unrelated words (PINES vs TULIPS), replicating past studies. At 250 msec SOA this prediction-related semantic facilitation was diminished. Thus, timing is a factor in determining the extent to which anticipatory mechanisms are engaged. However, we found evidence that prediction can sometimes be engaged even under speeded presentation rates. Participants who first read sentences in the 250 msec SOA block showed no effect of semantic similarity for this SOA, although these same participants showed the effect in the second block with 500 msec SOA. However, participants who first read sentences in the 500 msec SOA block continued to show the N400 semantic similarity effect in the 250 msec SOA block. These findings add to results showing that the brain flexibly allocates resources to most effectively achieve comprehension goals given the current processing environment.

Keywords: Event-related potentials; N400; Prediction; Sentence processing; Timing.

Figure 1

Grand average ERPs for the three sentence ending types in the 500 ms and 250 ms SOA conditions, shown for the 26 scalp recording sites. Negative is plotted up. The schematic head (nose at top) shows the arrangement. The N400 effect of expectancy (between-category vs. expected) is similar for the both SOA conditions, but the N400 effect of semantic similarity (between-category vs. within-category violation) is apparent for the 500 ms SOA and not the 250 ms SOA. (Electrode site abbreviations: Midline Prefrontal (MiPf), Left and Right Medial Prefrontal (LMPf and RMPf), Lateral Prefrontal (LLPf and RLPf), Medial Frontal (LMFr and RMFr), Mediolateral Frontal (LDFr RDFr), Lateral Frontal (LLFr and RLFr), Midline Central (MiCe), Medial Central (LMCe and RMCe), Mediolateral Central (LDCe and RDCe), Midline Parietal (MiPa), Mediolateral Parietal (LDPa and RDPa), Lateral Temporal (LLTe and RLTe), Midline Occipital (MiOc), Medial Occipital (LMOc and RMOc), and Lateral Occipital (LLOc and RLOc))

Figure 2

Topographic maps (based on spherical spline interpolation) of the expectancy effect and the similarity effect in each SOA condition show a medial central-parietal distribution typical of the N400.

Figure 3

Mean N400 amplitudes for the semantic similarity effect difference wave (Between category minus Within-category) in the 300–500 ms window post-stimulus onset, for the 250 ms SOA and the 500 ms SOA as a function of SOA block order. ERPs from the right mediolateral parietal site are shown below the bar graph for the two groups in both SOA conditions. Whereas both groups show the semantic similarity effect for the 500 ms SOA, only the group of participants who received the 250 ms SOA block after the 500 ms SOA shows evidence of a semantic similarity effect at the faster presentation rate. Negative is plotted up. Error bars represent standard error of the grand mean.