Teleology of motion sickness.

We investigated motion sickness evoked by walking while wearing horizontally reversing goggles. The subjects were 36 healthy adults and 90 children aged 4 to 15 years. Most adults soon displayed not only severe sickness, but also dizziness and instability. Instability was certified by Graybiel's ataxia tests in 10 adults. Young children aged 4 to 5 years rarely became sick; however, they showed marked ataxia manifested as drunken gait, falling, or failure to stand up. In older children, autonomic nervous symptoms became manifest and more severe, but ataxia became less severe since locomotion was stopped by uncomfortable symptoms. The present study strongly suggests that motion sickness makes animals learn loss of spatial orientation, which inevitably produces loss of balance.