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Effects of word length and frequency on the human event-related potential
Clinical Neurophysiology, 115(5), 1090-1103
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We investigated the influence of the length and frequency of printed words on the amplitude and peak latencies of event-related potentials (ERPs). This served two goals, namely (I) to clarify their possible effects as confounds in ERP experiments employing word-stimuli, and (II) to determine the point in time of lexical access in visual word recognition. EEG was recorded from 64 scalp sites while subjects (n=12) performed a lexical decision task. Word length and frequency were orthogonally varied between stimulus groups, whereas variables including regularity of spelling and orthographic tri-gram frequency were kept constant. Long words produced the strongest brain response early on (~100ms after stimulus onset), whereas those to short words became strongest later (150-360ms). Lower ERP amplitudes were elicited by words with high frequency compared with low frequency words in the latency ranges 150-190ms and 320-360ms. However, we did not find evidence for a robust alteration of peak latencies with word frequency. We conclude that length and frequency of word stimuli have independent and additive effects on the amplitude of the ERP. Studies on the precise time course of cognitive processes should consider their potentially confounding character. Our data support the view that lexical access takes place as early as 150ms after onset of written word stimuli.