The Cause and Practical Importance of Oculogravic Illusions

Abstract

The oculogravic illusion can be interpreted as a specific otolith response to a stimulus consisting of linear acceleration. It has been suggested as a conclusive proof that the phenomenon does not occur in deaf subjects with labyrinthine areflexia. Two fresh cases of acquired labyrinthine areflexia have been examined in the human centrifuge, the illusion being measured by a special technique. Although abnormal illusion curves much unlike those recorded in the congenitally deaf may be obtained at the end of the “destruction stage”, complete compensation with illusion curves resembling those of healthy individuals developed in a comparatively short time. The logical conclusion would be that oculogravic illusion cannot be accepted straight off as a selective measure for otolith sensitivity. In connexion with a discussion of analogies, comparing oculogravic and oculogyral illusion, the author suggests that the “lag effect” (i.e., the time necessary for reorientation on rapid changes of the angle of incidence of the resultant vector) may offer a more adequate expression for static sensibility. The recent advances in the methods of observing these labyrinthine illusions should add to our somewhat unverified knowledge of vestibular physiology and pathology.