Because we are psychologists studying the problem, we are often asked whether motion sickness is in the mind… “is it psychological?” The answer is that… “yes, it is.” But that's a qualified “yes.” It is in the mind in the same way that the central nervous system is the mind. Motion sickness is a disorder of the central nervous system, and it is believed to be due to sensory messages sent along input channels which either disagree with each other or with memory. We believe that to understand motion sickness we must understand how the stimulus is carried to the central nervous system and how it acts at the receptor level. Our view (that motion sickness is a result of decorrelated sensory channels) is in concert with the perceptual conflict theory. This theory states that any stimulus which causes a decorrelation to occur initiates the firing of the chemoreceptor trigger zone (CTZ), which leads to vomiting, the pathogmonic sign of motion sickness. This relationship can be schematized as follows:Decorrelated Receptors→CTZ→Motion SicknessWithin this perceptual conflict theory, correlations between sensory receptors build up over time. Decorrelation occurs when inputs are not in accord with what is expected from the neural store, or with the way in which that system is “hard-wired” to respond. This causes “trouble shooting” to begin. Trouble shooting may be analogous to the toxic reaction which develops when one is poisoned. Some people are more susceptible, perhaps analogous to being allergic, to certain toxic substances.Each sensory modality has channels and bandwidths of sensitivity. The conflict occurs when spatial (gain) and temporal (phase) aspects of the stimuli are not in accord. If the lack of accord occurs at places where the two channels are both sensitive, there is more disruption (poisoning) than at places where one or the other may be insensitive. Presumably, if discord occurs where both sensory modalities are insensitive, the stimuli are less toxic. This theoretical approach is in line with the ideas of other researchers. For example, Guedry (1968) asserts that there is a conflict within the vestibular system during head movements in space flight. It is also possible that there may be conflicts between two visual systems (Leibowitz & Post, 1982) during perceived forward motion in a flight simulator.