  When binocular rivalry is induced by opponent motion displays, perceptual
reversals are often associated with changed oculomotor behaviour (Frassle et
al., 2014; Fujiwara et al., 2017). Specifically, the direction of smooth
pursuit phases in optokinetic nystagmus (OKN) typically corresponds to the
direction of motion that dominates perceptual appearance at any given time.
Here we report an improved analysis that continuously estimates perceived
motion in terms of `cumulative smooth pursuit'. In essence, smooth pursuit
segments are identified, interpolated where necessary, and joined
probabilistically into a continuous record of `cumulative smooth pursuit'
(i.e., a probability of eye position disregarding blinks, saccades, signal
losses, and artefacts). The analysis is fully automated and robust in healthy,
developmental, and patient populations. To validate reliability, we compare
volitional reports of perceptual reversals in rivalry displays, and of physical
reversals in non-rivalrous control displays. `Cumulative smooth pursuit'
detects physical reversals and estimates eye velocity more accurately than
existing methods do (Frassle et al., 2014). It also appears to distinguish
dominant and transitional perceptual states, detecting changes with a precision
of $\pm100\,\mathit{ms}$. We conclude that `cumulative smooth pursuit'
significantly improves the monitoring of binocular rivalry by means of
recording OKN.
