A theory is presented supporting a geometrical explanation of physiological height vertigo as a 'distance vertigo' created by visual destabilization of posture when the distance between the observer and visible stationary contrasts becomes critically large. Though height vertigo is generally regarded as a psychopathological process, we hypothesize that it might instead result from an intersensory mismatch when visual information is at variance with vestibular and proprioceptive inputs. Psychophysical experiments confirming the hypothesis revealed that: 1) height vertigo is clearly related to body position, being the greatest in the upright stance; 2) it is the eye-object distance rather than the direction of gaze which is critical; 3) there is a saturation of height vertigo magnitude. Subjective vertigo increases with increasing altitude only below 20 metres. Physiological 'distance vertigo' must be distinguished from psychological 'acrophobia'. Its postural consequences may be ameliorated by strategies gleaned from knowledge of its mechanism such as providing nearby stationary contrasts in the peripheral visual field.

Adult↗

PubMedDate not supplied

The mechanism of physiological height vertigo. II. Posturography.

In order to validate the hypothesis that height vertigo is based on visual destabilization of free stance when the distance between eye and object becomes critically large, several of its consequences were demonstrated in posturographic experiments: (1) Visual signals conflicting with simultaneous vestibular and somatosensory inputs provided by sinusoidally tilting rooms may destabilize postural sway in the fore-aft as well as in the lateral direction. (2) In natural surrounding sway amplitudes increase with increasing eye-object distance up to 5 meters. Thus, teleologically, subjective height vertigo serves as an appropriate warning signal to withdraw the body from a stimulus situation inducing postural imbalance. (3) Postural height vertigo problems can be alleviated (a) by adjusting the head relative to the gravitational vector, and (b) by the presence of nearby stationary contrasts in the visual periphery according to the dominance of retinal periphery for dynamic spatial orientation.

Adult↗

PubMedDate not supplied

Cervico-vestibular and visuo-vestibular interaction. Self-motion perception, nystagmus, and gaze shift.

In 8 healthy subjects we studied self-motion perception and nystagmus due to sinusoidal stimulation (amplitude 90 degrees peak to peak, frequency 0.05 Hz) of the horizontal semicircular canals, the cervical proprioceptors, and the retina. We used an electrically driven rotatory chair and optokinetic drum combination. For cervical stimulation the subject's head was placed in a clamp, attached to the drum. Eye movements were recorded by means of electrooculography, d.c. amplification. Subjects signalled the estimated head position by means of a 'joystick'. In the present series of experiments the vestibular and cervical informations were played off against each other in combined stimulation conditions with an interstimulus phase lag of 0 to 315 degrees, in steps of 45 degrees. Similarly, the vestibular and visual informations were played off against each other. Concerning estimated head position, our main finding is that both the visually and the cervically induced illusion of head rotation overrule the vestibular sensation of head motion. The ocular response to combined vestibular plus cervical stimulation shows that both nystagmus slow phases and saccades of the cervical and the vestibular responses add up by vectorial summation.

Adult↗

PubMedDate not supplied

Compensation for labyrinthine defects examined by use of a tilting room.

Visual compensation for vestibular deficiency was demonstrated by stabilometry inside a laterally tilting room. Labyrinthless patients showed a predominance of vision over the somatosensory system for a rather long time: in contrast to the controls, the labyrinthless subjects experienced the tilting room often as stationary and the stationary stabilometer as tilting, which resulted in vertical postural instability.

Humans↗

PubMedDate not supplied

Somatosensory compensation for loss of labyrinthine function.

Somatosensory compensation for vestibular deficiency was demonstrated by stepping in circles in the dark. Stepping around in small circles provides a complex pattern of afferent somatosensory signals, which in combination represent the actual movement. Labyrinthless patients, i.e. patients devoid of labyrinthine function, reported during real as well as during apparent stepping around (on a rotating platform without stimulation of the canals) a strong sensation of rotation, as did the healthy subjects; they had a stronger somatosensory nystagmus than the healthy controls. In controls, the somatosensory and vestibular aftersensations cancelled, while the vestibular slightly outweighed their somatosensory afternystagmus . Labyrinthless subjects had no vestibulo- culomotor integrator function.

Electrooculography↗

PubMedDate not supplied

Arthrokinetic information affects linear self-motion perception.

A sensation of linear self-motion can be induced in a blindfolded stationary sitting subject, who keeps contact with a linearly moving platform (acceleration 0.1 m/s2) in the frontoparallel plane by means of a hand-over-hand walking action. When discordant suprathreshold vestibular information from the otoliths is added by moving the subject laterally (acceleration 0.1 m/s2) in the same direction as the platform (acceleration of the platform 0.2 m/s2, so the arthrokinetic stimulus is also an acceleration of 0.1 m/s2, but into the opposite direction), the arthrokinetic information was found to have a predominant effect on the perceived direction of self-motion.

Humans↗