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The Effects of Predictability and Stimulus Quality on Lexical Processing: Evidence from the Coregistration of Eye Movements and EEG

A word’s predictability has been shown to influence its processing. Two methodologies have demonstrated this time and again: eye tracking while reading and Event Related Potentials (ERPs). In eye tracking while reading, words that are made predictable by their contexts (as operationalized by the cloze task; Taylor, 1953) receive shorter first fixation times (Staub, 2015, for a review) as well as shorter gaze duration and increased skipping rate. In ERPs, the N400 component’s amplitude has also been shown to inversely correlate with a word’s predictability (Kutas and Federmeier, 2011, for a review). Despite the similarities, there is much reason to suspect that these two measures are reflections of different underlying cognitive processes, both modulated by a word’s predictability. We utilized the simultaneous collection of EEG and eye tracking data to investigate the differential effects of lexical predictability and stimulus quality on these measures. We found that these two manipulations had additive effects in the eye movement record, but yet only the manipulation of predictability influenced the N400 Fixation Related Potential (FRP) amplitude, with stimulus quality influencing neither the amplitude nor the latency of the N400. These findings provide no evidence for there being a role for predictability in early visual processing, and thus call into question the relative ordering of lexical processing effects laid out in Staub and Goddard (2019). Our findings also suggest that the N400’s underlying process is strictly temporally fixed and indexes the lexical processing difficulty left after there has already been a convergence of evidence towards the identity of the observed stimulus.
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