Polysynaptic pathways via the cerebellum are less efficient in transmitting such high acceleration vestibular stimuli.

Head impulses mainly drive the short latency, oligosynaptic VOR pathways from the semicircular canals to the extraocular muscles. This corrective saccade indicates a peripheral vestibular hypofunction on the side towards which the preceding head rotation occurred, provided ocular motor function is intact. If not (ie, in the case of a reduced gain of the VOR towards the side of the head impulse), a reflexive saccade back to the examiner's nose is performed after the end of the head thrust. If the peripheral vestibular system is intact and the vestibulo‐ocular reflex (VOR) operates normally, the patient's eyes keep their fixations approximately on target (ie, gaze is held relatively stable in space). The rotations are of low amplitude (10–20°) but of high acceleration (10000°/s 2). The patient is asked to fix upon a target straight ahead, usually the nose of the examiner, while the examiner turns the patient's head in the plane of a pair of semicircular canals. 1 Head impulses are rapid, passive, unpredictable rotations of the head relative to the trunk. The Halmagyi–Curthoys head impulse test is, at present, the only bedside examination that allows identification of the side of a unilateral hypofunction of the peripheral vestibular system.

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