Signal waveform examples under each of the experimental conditions for one participant.

<p>From top to bottom: trunk rotation velocity, head-trunk rotation velocity, head translation velocity, head rotation velocity, eye rotation velocity and retinal slip.</p

Retinal slip observed in the EFD-Stand, EFD-Walk, HFD-Stand, and HFD-Walk conditions.

<p>Error bars represent standard error.</p

Stimulus presentation material.

<p>(A) Numerical characters of the Digiface font; (B), a stimulus example; (C), the 500-ms mask.</p

Method used to calculate ideal eye pitch <i>β</i>_<i>xe</i> (see [2,27] for details and discussion).

<p><i>z</i>_<i>h</i>: vertical distance between the head rotation axis (black circle) and the target (black +), <i>α</i>_<i>x</i>: head pitch, <i>r</i>_<i>x</i>: distance between head rotation axis and eye rotation axis, <i>d</i>_<i>xz</i>: distance from the eye to the target.</p

Total relative variability observed in Experiment 1 (standard setting) and Experiment 2 (elastic force-field setting).

<p>Total relative variability (CVtotal) is expressed as the sum of temporal (CVtime) and spatial (CVspace) variabilities. Each task (Fitts and Schmidt) is presented separately.</p

Minimal stimulus presentation duration (MSPD) as a function of visual size for the EFD-Stand, EFD-Walk, HFD-Stand and HFD-Walk conditions.

<p>Error bars represent standard error. For each condition, the range of sizes revealing minimal duration thresholds is indicated by chequered textures.</p

Relations between temporal and spatial variabilities observed in Experiment 1 (standard setting) over the full movement and the constituent acceleration and deceleration phases.

<p>Space-time relations for absolute variability (A) and relative variability (B).</p

Analysis of Variance results for Experiment 1 (standard setting).

<p>ID =  Index of Difficulty. MTp =  prescribed movement time.</p

Relations between temporal and spatial variabilities observed in Experiment 2 (elastic force-field setting) over the full movement and the constituent acceleration and deceleration phases.

<p>Space-time relations for absolute variability (A) and relative variability (B).</p

Examples of hand positions used during wheel-throwing.

<p>The images were extracted from a video recording of an Indian Multani potter throwing a 2.25 kg sphere. From left to right and top to bottom, the positions were coded as numbers 1, 27, 28, 4, 5, 7, 23, 17, 11, and 20, respectively (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0081614#pone.0081614.s001" target="_blank">Supporting Information S1</a>).</p