Effects of word length and frequency on the human event-related potential

Objective: 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. Methods: 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. Results: Long words produced the strongest brain response early on ( 100 ms after stimulus onset), whereas those to short words became strongest later (150–360 ms). Lower ERP amplitudes were elicited by words with high frequency compared with low frequency words in the latency ranges 150–190 ms and 320–360 ms. However, we did not find evidence for a robust alteration of peak latencies with word frequency. Conclusions: 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 150 ms after onset of written word stimuli.