Vehicle motion characteristics differ between air, road, and sea environments, both vestibularly and visually. Effects of vision on motion sickness have been studied before, though less systematically in a naval setting. It is hypothesized that appropriate visual information on self-motion is beneficial in a naval setting and that task performance is likely reduced as sickness increases. Methods : Using a within-subjects design, 24 subjects were exposed to 30 min of motion in a ships bridge motion simulator with 3 visual conditions: an Earth-fixed outside view; an inside view that moved with the subjects; and a blindfolded condition. Subjective sickness symptoms and severity were rated repeatedly before, during, and after motion exposure. During the motion, subjects performed a mental task. Results : Though not excessive, sickness was highest in the inside viewing condition, intermediate in the outside viewing condition, and least in the blindfolded condition. The blindfolded condition was equally as bad as the inside viewing condition during the first 5-10 min of motion exposure. The overall temporal increase of sickness during motion was about equal to the decrease during recovery. No effect of sickness on task performance was observed. Discussion : Most sickness in a naval setting is observed when the visual environment moves with the subjects, as has been reported in other environments, such as cars. Only mild sickness, caused by moderate motions, was provoked in this study and was alleviated by the performance task. A non-linear brain mechanism integrating visual and vestibular information may explain why the least sickness was observed when subjects were blindfolded.