  Surprisal theory has provided a unifying framework for understanding many
phenomena in sentence processing (Hale, 2001; Levy, 2008a), positing that a
word's conditional probability given all prior context fully determines
processing difficulty. Problematically for this claim, one local statistic,
word frequency, has also been shown to affect processing, even when conditional
probability given context is held constant. Here, we ask whether other local
statistics have a role in processing, or whether word frequency is a special
case. We present the first clear evidence that more complex local statistics,
word bigram and trigram probability, also affect processing independently of
surprisal. These findings suggest a significant and independent role of local
statistics in processing. Further, it motivates research into new
generalizations of surprisal that can also explain why local statistical
information should have an outsized effect.
