Parafoveal preview effects depend on both preview plausibility and target predictability.

Recent studies using the boundary paradigm have shown that readers benefit from a parafoveal preview of a plausible continuation of the sentence. This plausibility preview effect occurs irrespective of the semantic or orthographic relatedness of the preview and target word, suggesting that it depends on the degree to which a preview word fits the preceding context. The present study tested this hypothesis by examining the impact of contextual constraint on processing a plausible word in the parafovea. Participants' eye movements were recorded as they read sentences in which a target word was either highly predictable or unpredictable. The boundary paradigm was used to compare predictable, unpredictable, and implausible previews. The results showed that target predictability significantly modulated the effects of identical and plausible previews. Identical previews yielded significantly more benefit than plausible previews for highly predictable targets, but for unpredictable targets a plausible preview was as beneficial as an identical preview. The results shed light on the role of contextual predictability in early lexical processing. Furthermore, these data support the view that readers activate a set of appropriate words from the preceding sentence context, prior to the presentation of the target word.