Psycholinguistic research based on the recording of eye movements during natural sentence reading has revealed that lexical processing involves activation of the current words that are being fixated on, as well as of upcoming words in readers’ parafoveal vision. The chapter discusses a fundamental issue in the reading of continuously written texts: Whether semantic, phonological, and morphological information from upcoming words is accessible during the reading of Korean sentences. Prime words that were related to the target word were presented parafoveally in the position of the target word. A saccade towards the target word triggered a display change, where the target word replaced the preview word immediately. Phonological, semantic, and morphological than unrelated previews led to shorter viewing time on the target word. Moreover, the readers exhibited a stronger phonological than semantic priming effect. Results indicate that readers adjust to different types of information from the linguistic environment to optimize reading.