Experimental conditions and procedure.

<p>Body and/or visual scene tilts are depicted for angles at which pointing movements were requested (i.e., 6, 12 and 18 deg) for each experimental condition (<b>S_fwd</b>, <b>S_bwd</b>, <b>B_fwdS</b>, <b>B_fwdS_bwd</b>, <b>B_fwdS_fwd</b>). Pink lines correspond to the visual scene orientations and dotted lines to the longitudinal body orientations. We mentioned the angle of visual scene orientation relative to the longitudinal body orientation (i.e., in a body-centered reference frame) as ‘S/b’ and relative to vertical as ‘S/v’ (i.e., in a gravity-centered reference frame). Associated single and combined conditions relative to the body-centered (i.e., body) and gravity-centered (i.e., g) reference frame are provided under each experimental condition. The lower panel of the figure illustrates the sequence of events including the different pointing blocks required during a trial (i.e., from 0 to 18 deg of body and/or visual scene tilt relative to the observer).</p

Final pointing position observed in combined conditions (solid lines) and associated predicted data (black dotted line) by the body-centered model.

<p><b>a</b>) Combined condition <b>B_fwdS_fwd</b> and predicted data by the unweighted sum. <b>b</b>) Combined condition <b>B_fwdS_bwd</b> and predicted data by this unweighted sum. Vertical bars denote positive standard errors. *: p<.05; ‡: p<.01; †: p<.001.</p

Kinematic parameters observed in conditions B_fwdS and B_fwdS_fwd (solid lines) and associated predicted data (black dotted line) by the gravity-centered model.

<p>Observed and predicted data for PA (<b>a,b</b>), rTPA (<b>c,d</b>), RT (<b>e,f</b>) and MD (<b>g,h</b>) were provided for both conditions (left panel: <b>B_fwdS_fwd</b>; right panel: <b>B_fwdS</b>). Vertical bars denote positive standard errors. The lines between conditions depict differences at a given angle. *: p<.05.</p

Kinematic parameters observed in combined conditions (solid lines) and associated predicted data (black dotted line) by the body-centered model.

<p>Observed and predicted data for PA (<b>a,b</b>), rTPA (<b>c,d</b>), RT (<b>e,f</b>) and MD (<b>g,h</b>) were provided for both combined conditions (left panel: <b>B_fwdS_fwd</b>; right panel <b>B_fwdS_bwd</b>). Vertical bars denote positive standard errors. The lines between conditions depict differences at a given angle and the bracket depicts an overall difference between conditions (i.e., effect of data type without interaction data type x angle of tilt). *: p<.05; ‡: p<.01; †: p<.001.</p

Theoretical gravitational torque at the centre of mass of the arm for each body tilt (0 to 18 deg) as a function of arm angular position relative to the shoulder horizon.

<p>Torque was provided from the arm starting position (mean arm position relative to the shoulder = -42 deg) to the final required arm position at eye level (mean arm position relative to the shoulder = 14 deg). Values correspond to an average subject of 70 kg with a 0.35 m upperarm, a 0.30 m forearm, a 0.20 m hand and eye-shoulder distance of 0.21 m.</p

Final pointing position observed in the conditions B_fwdS and B_fwdS_fwd (solid lines) and associated predicted data (black dotted line) by the gravity-centered model.

<p><b>a</b>) Combined condition <b>B_fwdS_fwd</b> and predicted data by this model. <b>b</b>) Combined condition <b>B_fwdS</b> and predicted data by this model. Vertical bars denote positive standard errors.</p

Peak acceleration (PA) as a function of condition and body and/or visual scene orientation (0 deg: white bars; tilted: coloured bars).

<p>Differences in planned comparisons between tilted vs. 0*: p<.05; ‡: p<.01; †: p<.001.</p

Movement pattern relative to orientation (0 deg vs. tilted).

<p><b>a</b>) Typical normalized acceleration profile relative to MD as a function of orientation (mean of all conditions). Differences in planned comparisons between tilted vs. 0 deg orientations were provided on the right panel for rTPA (<b>b</b>), RT (<b>c</b>), and MD (<b>d</b>). Vertical bars denote positive standard errors. *: p<.05; ‡: p<.01; †: p<.001.</p