Publisher's Synopsis
There are many different types of provocative motion that induce motion sickness syndrome. Most are associated with aids to locomotion-in particular, ships, hovercraft, aircraft, automobiles and trains; less commonly, elephants and camels. The complex accelerations generated by fairground amusements, such as swings, roundabouts (merry-go-rounds), roller-coasters and so on, can be highly provocative. In addition, many astronauts/cosmonauts suffer from motion sickness (space-motion sickness) when they first make head movements in the abnormal force environment (weightlessness) of orbital flight. The motion sickness syndrome is also produced by certain moving visual stimuli, without any physical motion of the observer; the external visual world display of fixed-base simulators (simulator sickness) or a large-screen projection of scenes taken from a moving vehicle (Cinerama or IMAX sickness) The essential characteristics of stimuli that induce motion sickness are that they generate discordant information from the sensory systems that provide the brain with information about the spatial orientation and motion of the body. The principal feature of this discord is a mismatch between the signals provided, principally, by the eyes and inner ear, and those that the central nervous system "expects" to receive and to be correlated.Several categories of mismatch can be identified. Most important is the mismatch of signals from the vestibular apparatus (labyrinth) of the inner ear, in which the semicircular canals (the specialized receptors of angular accelerations) and the otolith organs (the specialized receptors of translational accelerations) do not provide concordant information. For example, when a head movement is made in a car or aircraft which is turning, both the semicircular canals and the otoliths are stimulated in an atypical manner and provide erroneous and incompatible information, information that differs substantially from that generated by the same head movement in a stable, 1-G gravity environment. Likewise, low-frequency (below 0.5 Hz) linear accelerations, such as occur aboard ship in rough seas or in an aircraft during flight through turbulent air, also generate conflicting vestibular signals and, hence, are a potent cause of motion sickness.The mismatch of visual and vestibular information can also be an important contributory factor. The occupant of a moving vehicle who cannot see out is more likely to suffer from motion sickness than one who has a good external visual reference. The passenger below the deck or in an aircraft cabin senses motion of the vehicle by vestibular cues, but he or she receives visual information only of his or her relative movement within the vehicle. The absence of an "expected" and concordant signal in a particular sensory modality is also considered to be the essential feature of visually induced motion sickness, because the visual motion cues are not accompanied by the vestibular signals that the individual "expects" to occur when subjected to the motion indicated by the visual display.