In the terms of our model's policy parameters α and β described above, non-regressive policies are exactly those with β = 0, and a policy that is faster on the left-to-right pass but does make regressions is one with a lower value of α but a non-zero β .
we tested the performance of our model on the reading of a corpus of text typical of that used in reading experiments at a range of reasonable non-regressive policies, as well as a set of regressive policies with lower α and positive β .