[The eyes of the labyrinth]

Reliable knowledge of one's space is a prerequisite for effective action, and only sensory experience, although not alone sufficient, can provide access to knowledge of reality. All the diferent sensory modalities help to make sense of this mental construct, but visual information, when available, is predominant. This requires stable images and constant updating of one's awareness of gaze direction and position in space at the moment of acquisition. The vestibular system is sensitive to angular and linear accelerations and thus acts as a reference for stability--an inertial base which stabilizes and characterizes the gaze direction and encodes the subject's movement tracking. In clinical practice, loss of these capacities induces eye drift, nystagmus, oscillopsia, vertical eye misalignment and a shift in the representation of mental space, leading to dizziness, translational illusions, integration path error, and "senseless" perceptions of the self in space. The reaction time of the eye and of mental image stabilization is of the order of afew tens of milliseconds. Recent tools for vestibular exploration allow us to measure this reactivity, which is a determining factor for quality of life. The video head impulse test, dynamic visual acuity, and cervical vestibular evoked myogenic potentials explore the structures involved in gaze and image stabilization, while subjective visual vertical and ocular vestibular evoked myogenic potentials provide an approach to the utricular contribution. This clinical and instrumental semiology sometimes proves more sensitive than the most advanced and accurate medical imaging methods, but rational listening and multidisciplinary skills on the part of the physician remain necessary to identify "self in space perceptual alterations.