Predictability's aftermath: Downstream consequences of word predictability as revealed by repetition effects

Abstract

Stimulus processing in language and beyond is shaped by context, with predictability having a particularly well-attested influence on the rapid processes that unfold during the presentation of a word. But does predictability also have downstream consequences for the quality of the constructed representations? On the one hand, the ease of processing predictable words might free up time or cognitive resources, allowing for relatively thorough processing of the input. On the other hand, predictability might allow the system to run in a top-down "verification mode", at the expense of thorough stimulus processing. This electroencephalogram (EEG) study manipulated word predictability, which reduced N400 amplitude and inter-trial phase clustering (ITPC), and then probed the fate of the (un)predictable words in memory by presenting them again. More thorough processing of predictable words should increase repetition effects, whereas less thorough processing should decrease them. Repetition was reflected in N400 decreases, late positive complex (LPC) enhancements, and late alpha/beta band power decreases. Critically, prior predictability tended to reduce the repetition effect on the N400, suggesting less priming, and eliminated the repetition effect on the LPC, suggesting a lack of episodic recollection. These findings converge on a top-down verification account, on which the brain processes more predictable input less thoroughly. More generally, the results demonstrate that predictability has multifaceted downstream consequences beyond processing in the moment.

Keywords: Alpha power; Repetition; Sentence comprehension; Word predictability.

Figure 1

Schematic of the electrode montage with labels.

Figure 2

Grand-average ERPs time-locked to words upon initial presentation. Words were predictable (presented in strongly constraining sentence contexts) or unpredictable (presented in weakly constraining sentence contexts). Negative is plotted up in all ERP figures. A) All scalp electrode sites; the position of the channels in the figure approximates the position on the head, with the nose at the top. B) Close-ups of a central channel (MiCe) showing the N400, and of a frontal channel (LMPf) showing the post-N400 effect. Shading reflects unbiased within-subjects SEM (Cousineau, 2005; Morey, 2008). Insets show scalp topographies of the difference (Unpredictable – Predictable).

Figure 3

Grand-average ERPs time-locked to sentence-final words in the critical weakly constraining sentences. The words were either repetitions (Previously Predictable, Previously Unpredictable) or unseen words presented in the same sentence contexts (Not Previously Seen). A) All scalp electrode sites. B) Close-up of a right medial channel (RMCe) showing the N400 and LPC. Shading reflects unbiased within-subjects SEM (Cousineau, 2005; Morey, 2008). Scalp topographies show the repetition effect for previously unpredictable words, the repetition effect for previously predictable words, and the effect of prior predictability.

Figure 4

Grand-average time-frequency representations of power and inter-trial phase clustering (ITPC) time-locked to word onset at initial presentation. Spectrograms of individual conditions and their difference are shown along with the scalp topography of the difference. A) Power changes relative to a −500 to −150 ms baseline at a frontal channel (LMFr; indicated with a black dot in the scalp map). Power was similar for Predictable and Unpredictable words, as shown in the bottom panel (difference relative to the average across all conditions). B) Inter-trial phase clustering at a parietal channel (MiPa; indicated with a black dot in the scalp map). The contour line in the spectrogram indicates cluster extent in permutation tests of the difference.

Figure 5

Grand-average time frequency representations of power time-locked to final words in the critical sentences, at an occipital channel (LLOc; indicated with a black dot in the scalp maps). The top panels show power changes relative to a −500 to −150 ms baseline within each condition. The bottom panels show power differences (relative to the average across all conditions) and their scalp topography. Contour lines indicate cluster extent in permutation tests. A) Repetition effect for previously unpredictable words. B) Repetition effect for previously predictable words. C) Numerical effect of prior predictability.