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False perception of the motions of the self and/or external objects in the physical world may be provoked by neurological disease or by unusual conditions of motion and environmental structure. For example, peripheral vestibular disease may result in the illusion that self and the environmental surrounds are rotating. In contrast, a normal subject whilst flying an aircraft, blind in cloud, may feel that he is flying on a straight course when in fact he is in a prolonged turn.' In both cases, the sensory inputs which are normally combined to provide an accurate model of the physical world provide false information because either the stimuli are unphysiological or important sensory information is lacking or distorted. The resulting misleading sense of movement and disorientation may be associated with other somatic symptoms such as nausea, sweating and a sense of anxiety and panic.2 This article documents an unusual group of four patients with minimal symptoms of neuro-otological disease who become disorientated when they drive a car in particular environmental conditions. For comparison, two others in whom steering was impaired by vestibular disease are described. The four patients presented to

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We describe six patients who, as teenagers or adults, developed florid nystagmus with consequent visual symptoms without any other manifestation of disease. In three patients, previous ophthalmologic examination had excluded nystagmus, and there was medically informed witness to its onset. The remainder may or may not have had a milder, unsuspected nystagmus before the development of symptoms. Ophthalmologic and neurologic investigations were negative, and follow-up of 2 to 15 years has been uneventful. Eye movement recordings showed the characteristics of the nystagmus to be indistinguishable from congenital nystagmus, which normally becomes manifest in early infancy. We conclude that a congenital-type nystagmus can emerge or enhance in later life without apparent provocation and is probably associated with a benign pathophysiology.