Performance and sickness at sea

Human performance at sea generally decreases with increasing severity of seasickness. Seasickness predictions can be made, be it that motions are assumed to be translational along a vertical axis only and sinusoidal. Here, a deterministic model is presented based on physiological knowledge of the vestibular (equilibrium) system. This model is based on the facts that 1) people without a functioning inner ear do not get sick from motion, 2) motion sickness only arises when gravity changes with respect to a subject's head, and 3) expectation and experience play a key role. By analysing a systems theoretical concept restricted to vertical motions, vestibular inputs, and passengers only, this model predicts sickness incidence as it is observed. Theoretically it is, however, also capable of predicting motion sickness in response to any kind of motion. Because a mere description of sickness incidence in response to all different (spatio-temporal) kinds of motion is hardly attainable, this fundamental approach has great advantages.