the otoconia shift, which stimulates the cupula to send false signals to the brain, producing vertigo and triggering nystagmus. In addition to vertigo, symptoms of BPPV include dizziness, imbalance, difficulty concentrating, and nausea. The otolithic membrane can be affected in patients with Ménière's disease. Sudden falls without loss of consciousness (drop attacks) may be experienced by some people in the later stages of the disease, when they are referred to as Tumarkin attacks, or as Tumarkin's otolithic crisis. Those who experience such attacks (probably less than 10% of people with Meniere's disease) may report a sensation of being pushed sharply to the floor from behind. The phenomenon is thought to be triggered by a sudden mechanical disturbance of the otolithic membrane that activates motoneurons in the vestibulospinal tract. Otolithic function can also be compromised after unilateral vestibular neurectomy. The illusion is that during centrifugal stimulation, a small luminous bar, fixed with respect to the observer, appears to be roll-tilited by the same amount that the observer feels to be roll-tilted. This illusion is felt symmetrically in normal patients, but after vestibular neuroectomy, patients perceive a reduce illusion when the force is directed toward their operated ear. Other animals Otolithic membrane structure has been frequently studied in amphibians and reptiles in order to elucidate the differences and to understand how the membrane has evolved in various otolith organs. Otolithic membranes of utricles in reptiles and amphibians represent thin plates of non-uniform structure, while the otolithic membrane in the saccule resembles a large cobble-stone-like conglomerate of otoconia. In fish, amphibians and reptiles there is also a third otolith organ that is not present in humans, and is called the lagena. The otolithic membrane in the lagena of amphibians is poorly differentiated, but well differentiated in reptiles. This difference corresponds to the fact that when vertebrates began to inhabit the earth surface there was a reorganization of the membrane. Over time, there was two changes that occurred in parallel when referring to the evolution of the otolithic membrane. First, otoliths that were present in amphibians and reptiles were replaced by a structurally differentiated otolithic membrane. Second, the spindle-shaped aragonitic otoconia were replaced by calcitic barrel-shaped otoconia. These two changes are referred to as the two directions of evolution of the otolithic membrane. Research Finite element models There are currently several techniques to model the otolithic membrane that all serve as a way for