Dynamic displacement trials were then collected to measure changes in inter-marker distance due to vertical elongation of the gel liner.
This experimental trial followed the displacement test.
Pursuit was controlled by moving the fixation task within a third of width and height of the screen with an unequal number of cycles of sinusoidal displacement per trial in horizontal and vertical axes, respectively (randomly assigned 3 or 4 cycles, each with random initial phases).
It was always the same pole that was displaced throughout a whole run although the displacement varied from trial to trial.
This design allowed us to directly compare the amount of illusory displacement on trials matched for angular disparity, but differing in biomechanical constraints.
At the trial displacement figure of 38400 LT, even 186,000 shp would be enough; the 210,000 figure was derived from a 12.5% overestimation to account for a fouled bottom or bad weather.
The total displacement of each trial was 20 cm.
We used a customized algorithm based on MATLAB® (The MathWorks, Inc., Natick, MA, USA) to calculate angular displacement for each trial.
The relative phase relationship between the time of maximum (up-on-the-beat trials) or minimum (down-on-the-beat trials) displacement for each movement cycle, and the metronome beat, was derived using standard methods [8].
As shown in Fig. 3b (left), there was substantially greater postural displacement in incongruent trials with mirror vision compared to other conditions, which led to a main effect of postural congruence (incongruent: M = 41.06°, SD = 28.44°; congruent: M = 3.54°, SD = 7.23°), p < 0.001, as well as a significant vision by postural congruence interaction, p < 0.001.
