In labyrinthine deficiency, the vestibulo-ocular reflex (VOR) is supplemented by corrective saccades that bring gaze back toward the intended fixation target. These saccadic corrections may be triggered while the head is still rotating (covert saccades) or after it has stopped (overt saccades). Covert saccades are generally considered to be triggered open-loop, before the availability of visual information, based on vestibular and possibly proprioceptive signals. Here, we used an automated head impulse test device to reduce the variability of vestibular information and studied gaze error and covert saccade latencies in a population of acute unilateral vestibular patients in response to two paradigms: one in which the head impulse parameters were unpredictable and one in which the direction, timing, and amplitude of the head rotation were known to the patients. We found that predictability increased the gain of the VOR and reduced the gaze error at the onset and at the end of covert saccades, as well as at the end of the head rotation. Further, we found that covert saccades present with two subpopulations: those triggered before 90–100 ms and those triggered later. Covert saccades are more likely to occur in predictable than in unpredictable trials and the ratio of those occurring early, with a latency below 100 ms, increases in predictable head impulses. We analyzed the distributions of saccade latencies in the two paradigms with a Linear Approach to Threshold with Ergodic Rate (LATER) analysis approach and successfully interpreted the findings using a LATER model comprising two decision units, each producing a rise-to-threshold decision signal competing with the other to trigger the saccade. The change of early covert saccadic distribution in predictable trials was successfully modeled as an increase of the prior probability for the early decision mechanism, reflecting the greater confidence in the vestibular signal due to expectation.