A system, including: one or more sensors included in an apparatus wearable by a vehicle operator to measure ocular muscle movement； and a computer that includes a processor and a memory, the memory storing instructions executable by the computer such that the computer is programmed to: receive data indicating ocular muscle movement from the wearable sensor； determine, using the measurement, a gaze direction of the operator； use the gaze direction to determine a level of operator attentiveness； and actuate a vehicle operation if the level of operator attentiveness is below a predetermined threshold.
