This illusion is quite rare and I can remember on my fingers the patients with it whom I met, generally in emergency settings. For the majority of them the illusion was transitory lasting generally minutes and was accompanied by other neurological symptoms and deficits (vestibular and not).
The room-tilt illusion consists of a clear and bright visual view of an upside down tilt (180 degree on a coronal plane) of the surroundings. Even if in an upside down way, the walls and the objects of the room are perfectly perceived, without probably no distortion (or some sort of rotation). The patients are usually frightened about that illusion and think to have stoke.
This illusion is generally considered the results of a lesion or dysfunction in the brainstem circuitries that connect the vestibular-otholitic system (the inner ear organ of equilibrium) to the higher brain associative visual areas (parieto-temporal regions and posterior insula). According to this last assumption, the room-tilt illusion is a syndrome of the higher central vestibular functions. However the exact neural mechanism of the room-tilt illusion is not yet known.
Finally for the majority of these patients (as the ones I met in my profession) the responsible lesion is ischemic (AIT or stroke) and located in the lower brainstem areas. However, the syndrome is known to occur less frequently with pure vestibular disorders (such as Meniere disease, bilateral vestibular affections or benign positional paroxysmal vertigo), and also as a partial epileptic crisis (vestibular epilepsy) in patients with cortical lesions.
I found the illusion also in a patient with multiple sclerosis whose neurological deficits worsened after a urinary infection, and in a patient with migraine who was hyperventilating during the migraine crisis. In the scientific literature, the illusion has been described also in isolated patients with Parkinson’s disease, cervical myelopathy, polyradiculoneuritis and cerebellar diseases (ischemic or degenerative).
Finally patients with the room-tilt illusion have an upside-down misperception of verticality. In normal conditions the dimension of verticality is assured by an accurate interaction between the vestibular system (together with other sensory afferent inputs) and the visual system. The results of such neural processing is adapted to 3-D coordinates of the self and of the visual scene. When there is a mismatch between vestibular peripheral inputs (altered by the lesion) and the other sensory systems, the higher cortical centers (visual associative areas) must re-calibrate these abnormal signals and could do it with the result of a complete scene inversion on the coronal roll plane.
The room-tilt illusion is a rare symptom, and generally it is transitory. Therefore, it would be quite difficult to study it with experimental paradigms, such as for example (the first one that came to my mind) measuring the speed and quality of reading of inverted and not inverted degraded words. We know that rotation of a furnished room in controlled conditions can reproduce the illusion only partially in normal subjects.
We are so accustomed to see the visual world as it is that we are not aware at all of the complexity of the information that the brain process (in multiple regions) in order to let things appear at the right places. When the brain is damaged in his visual association areas the visual world changes, then we realize how much fragile is the consciousness and the awareness of the self. Things probably do not exist as they appear when they are not processed correctly by a visual brain.
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