The resulting χ 2 statistic indicates the extent to which each surprisal estimate accounts for RT, and can thus serve as a measure of the psychological accuracy of each model.
this kind of analysis assumes that RT for a word reflects processing of only that word, but spill-over effects (in which processing difficulty at word w t shows up in the RT on w t+1 ) have been found in self-paced and natural reading (Just et al., 1982;Rayner, 1998;Rayner and Pollatsek, 1987).