Early correlates of word recognition in fixation-related and event-related potentials: A comparison using simultaneous eye-tracking and EEG

Electrophysiological correlates of visual word recognition have typically been studied with single-word paradigms, or using word-by-
word presentation (RSVP). An alternative approach to study word recognition under more natural conditions is to record fixation-related potentials (FRPs) time-locked to individual fixations during saccadic reading. While previous research has demonstrated the feasibility of this approach, existing FRP studies have focused on late and comparatively easy-to-measure components in the N400 latency range. The goal of the present study was to test for early effects of word frequency in FRPs and to compare their timing to effects in conventional event-related potentials (ERPs). Eye movements and EEG were simultaneously recorded while participants read lists of unrelated German nouns, which varied in terms of their word frequency. In half of the trials, participants read the lists in a normal, left-to-right fashion. In the other half, lists were presented in RSVP at a pace matched to reading speed in the FRP condition. To control for influences of correlated word properties (e.g. length) and oculomotor behavior, linear mixed models (LMMs) were specified for each sampling point of the event-related EEG. Word frequency modulated fixation duration and had two temporally separable effects in the FRP: One peaking at 550 ms after fixation onset, and one around 200 ms, that is, during the duration of the first fixation. Both effects were replicated with traditional RSVP presentation. Results suggest that it is feasible to identify early EEG correlates of lexical processing under natural reading conditions, allowing direct comparisons between EEG measures and fixation time.