Abstract
Fluent reading may require rapid and automatic processing of letter strings. To examine this automaticity, Okumura et al. (2014) recorded event-related potentials in response to rapidly-presented and task-irrelevant letter-strings (word, nonword) and symbols. They found a negative enhancement specific to letter strings at bilateral posterior temporal sites in 150-200 ms after stimulus onsets (bilateral N170). However, the presentation frequency of letters and non-letters was not the same in this experiment (2:1), which may have confounded the results. Thus, the present study conducted an improved similar experiment at this point, and the results differed considerably: we observed a word-specific positive enhancement in 80-120 ms over posterior temporal sites, which was followed by the typical letter-specific left-lateralized N170 and a novel enhanced parietal negativity for nonwords in 150-200 ms. These results suggest that there are multiple early stages of processing for letter strings, which are driven by stimulus context.
