Behavioral contagion in an experimental motion environment.

BACKGROUND: It is generally understood that whole-body movement up and down can produce motion sickness. A standard reference, published in this journal in 1974, found that a frequency of 6 cycles per minute was most productive of motion sickness. The 1974 study used a vertical oscillator carrying two subjects at a time. The investigators were, of course, aware that the sight, sound, or smell of another person being ill might itself contribute to sickness. Accordingly, the two subjects were located in completely separate compartments, each soundproofed and with its own independent air-conditioning system. The sessions were scheduled to last 2 h. However, if a subject "pre-terminated" (became ill or requested removal), the oscillator was stopped while the subject debarked. METHODS: The present study is a secondary analysis of data elements not reported in the original study, namely, the frequency of pairs in which 0, 1, or 2 subjects pre-terminated. If knowing that the other subject had pre-terminated had no effect on whether the remaining subject pre-terminated, then the pairs in which 0, 1, or 2 subjects pre-terminated should be distributed binomially. RESULTS: Independent pre-termination of the two subjects in a pair was rejected (p < 0.001). The likelihood that a subject would pre-terminate increased strongly when the subject's partner pre-terminated. This effect was twice as large when the motions of the oscillator were severe as when they were less severe. CONCLUSIONS: Pre-termination by one subject legitimized pre-termination by example, and thereby increased the risk that the remaining subject would also pre-terminate (behavioral contagion).