  Human reading behavior is tuned to the statistics of natural language: the
time it takes human subjects to read a word can be predicted from estimates of
the word's probability in context. However, it remains an open question what
computational architecture best characterizes the expectations deployed in real
time by humans that determine the behavioral signatures of reading. Here we
test over two dozen models, independently manipulating computational
architecture and training dataset size, on how well their next-word
expectations predict human reading time behavior on naturalistic text corpora.
We find that across model architectures and training dataset sizes the
relationship between word log-probability and reading time is (near-)linear. We
next evaluate how features of these models determine their psychometric
predictive power, or ability to predict human reading behavior. In general, the
better a model's next-word expectations, the better its psychometric predictive
power. However, we find nontrivial differences across model architectures. For
any given perplexity, deep Transformer models and n-gram models generally show
superior psychometric predictive power over LSTM or structurally supervised
neural models, especially for eye movement data. Finally, we compare models'
psychometric predictive power to the depth of their syntactic knowledge, as
measured by a battery of syntactic generalization tests developed using methods
from controlled psycholinguistic experiments. Once perplexity is controlled
for, we find no significant relationship between syntactic knowledge and
predictive power. These results suggest that different approaches may be
required to best model human real-time language comprehension behavior in
naturalistic reading versus behavior for controlled linguistic materials
designed for targeted probing of syntactic knowledge.
