Interaction of top-down category-level expectation and bottom-up sensory input in early stages of visual-orthographic processing

Abstract

How and when top-down information modulates visual-orthographic processing is an essential question in reading research. In a previous study, we showed that task modulation of print-tuning started at around 170 ms after stimulus presentation in the N1 offset of the ERP, while the N1 onset was yet unaffected. Here we test how prior category-level expectation affects visual-orthographic processing. Familiar, left/right-structured Chinese characters and stroke number matched, unfamiliar Korean characters were presented, while expectation about the upcoming stimuli was manipulated with green and blue colored frames (high Chinese vs. high Korean expectation). EEG data of 18 native Chinese speakers were recorded while participants performed an expectation judgment task. Results from occipito-temporal and whole map analyses revealed that effects of prior expectation changed throughout the N1. Accordingly in the N1 onset, a print tuning main effect was found, with a stronger N1 to Chinese characters than Korean characters, irrespective of expectation. In the N1 offset, an expectation-by-character interaction was observed at the whole map level, with a more negative N1 to Korean characters than Chinese characters when expecting a Chinese character, but no such difference when expecting a Korean character. Moreover, the expectation-by-character interaction continued to the N250, with similar responses to Chinese and Korean characters under the Chinese expectation condition, while less negative N250 to Korean than Chinese under the Korean expectation condition. Taken together, the current study provides evidence that prior category-level expectation starts to take effect at an early stage even within 200 ms by facilitating the processing of expected stimuli, suggesting that category-level expectation can influence early visual-orthographic processing during word recognition.