Biomedical subjects
G de Wit
Publications and source records attributed to G de Wit.
Posturography as an auxiliary in vestibular investigation.
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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.
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.
The "marche-en-étoile" revised. The influence of after-images and prism-glasses on starwalks.
An analysis of the role that casual after-images play in starwalk (marche-en-étoile) tests, shows that these can be turned from unreliable into reliable tests. The vestibular function test described in this article is as follows: (a) the individual walks with open eyes to a point of reference 5 m distant. On arrival, he closes his eyes and walks backward and forward according to the marche-en-étoile procedure. (b) Same procedure as (a), but now the orientation point is replaced by a light source that is switched off when the patient reaches it. (c) Same procedure as (b), but now the patient is wearing prism-glasses. It turns out, the deviations in the starwalk are caused mainly by drifting of the after-image. This drift is based on an oculogyral illusion, and it appears that it can be influenced by wearing prism-glasses. These investigations reveal the existence of hitherto too little known interactions between the vestibular and the visual system.