A vestibular caloric test or caloric reflex test tests the reflex that allows the eyes to remain focussed on a subject by having the eyes automatically move in the opposite direction that the head moves. It involves irrigating the outer canal of the ear (between the eardrum and the opening of the ear) with either cold or warm water using a syringe.
The water is a different temperature than the body. As such, the water in the ear creates a convective current in the ear which the brain mistakes for movement of the head. Warm water is perceived as movement in the direction away from the ear being tested, and cold is perceived as movement in the direction towards the ear being tested. In a patient with a normal reflex, the eye will turn the opposite way. The acronym to remember this is COWS - Cold Opposite, Warm Same.