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. 2013 Jun 19;8(6):e66949.
doi: 10.1371/journal.pone.0066949. Print 2013.

Getting Your Sea Legs

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Free PMC article

Getting Your Sea Legs

Thomas A Stoffregen et al. PLoS One. .
Free PMC article

Abstract

Sea travel mandates changes in the control of the body. The process by which we adapt bodily control to life at sea is known as getting one's sea legs. We conducted the first experimental study of bodily control as maritime novices adapted to motion of a ship at sea. We evaluated postural activity (stance width, stance angle, and the kinematics of body sway) before and during a sea voyage. In addition, we evaluated the role of the visible horizon in the control of body sway. Finally, we related data on postural activity to two subjective experiences that are associated with sea travel; seasickness, and mal de debarquement. Our results revealed rapid changes in postural activity among novices at sea. Before the beginning of the voyage, the temporal dynamics of body sway differed among participants as a function of their (subsequent) severity of seasickness. Body sway measured at sea differed among participants as a function of their (subsequent) experience of mal de debarquement. We discuss implications of these results for general theories of the perception and control of bodily orientation, for the etiology of motion sickness, and for general phenomena of perceptual-motor adaptation and learning.

Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Figure 1
Figure 1. Experiment 1: Mean stance width (the distance between the midline of the heels) as a function of days.
The figure illustrates the statistically significant effect of days. The error bars represent standard error of the mean.
Figure 2
Figure 2. Setting and conditions for body sway testing.
A. Viewing of the nearby target and the horizon at the dock. B. Viewing of the nearby target and the horizon at sea.
Figure 3
Figure 3. Experiment 2: Mean positional variability of the COP as a function of days.
The figure illustrates the statistically significant effect of days. The error bars represent standard error of the mean.
Figure 4
Figure 4. Experiment 2: Mean positional variability of the COP during viewing of the nearby target and the horizon, as a function of days.
The figure illustrates the statistically significant interaction between target distance (nearby target vs. horizon) and days. The error bars represent standard error of the mean.
Figure 5
Figure 5. Experiment 2: Mean positional variability of the COP for the AP and ML axes, as a function of days.
The figure illustrates the statistically significant interaction between axes and days. The error bars represent standard error of the mean.
Figure 6
Figure 6. Experiment 2: Meanα of DFA as a function of days.
The figure illustrates the statistically significant effect of days. The error bars represent standard error of the mean.
Figure 7
Figure 7. Experiment 2: Meanα of DFA for the AP and ML axes as a function of days.
The figure illustrates the statistically significant interaction between axes and days. The error bars represent standard error of the mean.
Figure 8
Figure 8. Experiment 3: Mean symptom ratings for the three seasickness severity groups as a function of days.
The error bars represent standard error of the mean.
Figure 9
Figure 9. Experiment 3: Mean stance width (distance between the midlines of the heels) on Day 1 at sea, as a function of seasickness severity groups.
The figure illustrates the statistically significant effect of seasickness severity groups. The error bars represent standard error of the mean.
Figure 10
Figure 10. Experiment 3: Meanα of DFA on Day 0 (before the voyage began) for the three seasickness severity groups.
The figure illustrates the statistically significant effect of seasickness severity groups. The error bars represent standard error of the mean.
Figure 11
Figure 11. Experiment 3: Meanα of DFA on Day 0 (before the voyage began) during viewing of the nearby target and the horizon, for the three seasickness severity groups.
The figure illustrates the statistically significant interaction between seasickness severity groups and visual targets (near target vs. horizon). The error bars represent standard error of the mean.
Figure 12
Figure 12. Experiment 4: Mean positional variability in the AP and ML axes for participants who experienced mal de debarquement for less than 30 minutes (the Low-MD group) or more than 120 minutes (the High-MD group).
The figure illustrates the statistically significant main effect of groups (<30 minutes vs. >120 minutes), and the statistically significant interaction between groups and body axes (AP vs. ML). The error bars represent standard error of the mean.

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Supplementary concepts

Grant support

The study was supported by the University of Minnesota, the University of Montpellier-1, the University of Sao Paulo, and National Pingtung University of Science and Technology. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
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