Mask-related costs in measuring preview benefit: Evidence from a distributional analysis based on target word reading times.

Skilled reading involves processing the upcoming word in parafoveal vision before it is fixated, leading to shorter fixations on that word. This phenomenon, parafoveal preview benefit, is a key component of theoretical models of reading; it is measured using the invisible boundary paradigm, in which reading times on a target word are compared for instances when preview is accurate and when the target word is masked while in the parafovea. However, parafoveal masks have been shown to induce unintentional processing costs, thereby inflating measures of preview benefit. The degraded mask has been explored as a potential solution to this problem, leading to mixed results. While previous work has analyzed the preview effect by comparing mean reading times on the target word, the present study provides a more comprehensive analysis by examining the distribution of the preview effect across target word fixation times for unrelated and degraded masks. Participants read sentences containing target words whose preview was either identical, unrelated, or degraded, and their eye movements were recorded. Analyses revealed that although there were no mean differences between reading times for the unrelated and degraded conditions, the pattern of the effects varied as a function of target word fixation times. Unrelated masks resulted in positively sloped generally linear delta plots, while degraded masks resulted in relatively flat delta plots for fixations longer than 200 ms. These differences suggest that different cognitive mechanisms are involved in the processing of the two mask types. Implications for understanding and measuring preview benefit are discussed.