Modulation of vergence during the vestibulo-ocular reflex

It is commonly believed that during the compensatory slow-phases of the vestibulo-ocular reflex (VOR), eyes move in a perfectly conjugate fashion (i.e. the vergence component is zero). Consequently, VOR measurements are often restricted to either conjugate recordings or to single eye recordings. During binocular recordings of the angular VOR in the dark, we observed a significant vergence component even in normal subjects. More interestingly, the measured vergence component modulated with head velocity. The modulation of vergence during the VOR in the dark could imply a vestibular contribution to vergence. These observations suggest a shared central controller for both version and vergence.