Article Figures & Data
Figures
- Figure 1.
Experimental methods. (A) Experimental setup. Participants performed reaching movements in the horizontal plane while holding on to the handles of the robotic manipulandum. (B) Example bimanual nonchannel trial of experiment 1. Participants were instructed to fixate on the left or right reach target. Reach targets could be both narrow (in blue) or wide (in red). On a subset of trials, one of the hand cursors was visually displaced to the left or right after it passed under a visual occluder, requiring a correction of the movement trajectory. (C) Cursor paths from an example participant in response to a leftward (in green), zero (in gray), and rightward (in blue) shift of the left-hand cursor during bimanual reaching to narrow targets in nonchannel trials. (D) Same as C, but with reaching to wide targets (orange, leftward cursor shift; gray, no cursor shift; red, rightward cursor shift). (E) Example bimanual force channel trial of experiment 1. Participants’ hand movements were constrained along a straight line from start to target position, allowing us to measure the forces applied into the virtual wall of the channel (depicted by the black dashed lines). In cursor perturbation trials, the cursor automatically moved back to this line 250 ms after the perturbation. (F) Example bimanual force channel trial of experiment 2. Participants were instructed to fixate on a central fixation target. On a subset of trials, a single or both hand cursors were visually displaced to the left or right.
- Figure 2.
Visuomotor responses in experiment 1. (A) Raw forces measured in channel trials in response to a leftward (–3 cm; in green and orange) and rightward (3 cm; in blue and red) displacement of the visual cursor during reaches to narrow (top row) and wide targets (bottom row) of the same example participant as in Fig. 1. (B) Difference in force responses to leftward and rightward cursor perturbations during reaches to narrow (in blue) and wide targets (in red), averaged across participants. Blue and red shaded areas indicate ±1 SEM. The black vertical line indicates the average onset of the corrective response (see Methods). The gray shaded area indicates the 180- to 230-ms interval across which the force differences were averaged to obtain a single measure of the strength of the response. (C) Mean force differences averaged across the 180- to 230-ms interval following the cursor perturbation. Error bars represent ±1 SEM. (D) Mean force differences at the nonperturbed hand in bimanual conditions.
- Figure 3.
Visuomotor responses in experiment 2. Bars represent the mean force differences at a single hand averaged across the 180- to 230-ms interval following the cursor perturbation. Error bars represent ±1 SEM. Target sizes in parentheses indicate the size of the target of the other hand.
Tables
Experiment Variable Statistical test Factor or comparison Test values 1 Corrective force differences 2 × 2×2 repeated-measures ANOVA TWFSHTW×FIXTW×HFIX×H F(1,13) = 173.0, p < 0.001, OP = 1.0F(1,13) = 59.0, p < 0.001, OP = 1.0F(1,13) = 17.6, p = 0.001, OP = 0.97F(1,13) = 33.4, p < 0.001, OP = 1.0F(1,13) = 1.5, p = 0.238, OP = 0.21F(1,13) = 1.4, p = 0.262, OP = 0.19 1 Ratio of corrective force differences 2 × 2 repeated-measures ANOVA FIXHFIX×H F(1,13) < 0.1, p = 0.976, OP = 0.05F(1,13) = 0.1, p = 0.746, OP = 0.06F(1,13) = 0.27, p = 0.611, OP = 0.08 1 Corrective force differences at nonperturbed hand One-sample t-tests (corrected α = 0.0125) nt+fixnt+nfixwt+fixwt+nfix t(13) = 4.2, p = 0.001, CI [0.06–0.19]t(13) = 3.7, p = 0.003, CI [0.04–0.15]t(13) = 2.2, p = 0.050, CI [<0.0001–0.15]t(13) = 1.5, p = 0.157, CI [–0.02 to 0.11] 1 Correction onsets (t-test method) 2 × 2 repeated-measures ANOVA FIXHFIX×H F(1,13) = 120.4, p < 0.001, OP = 1.0F(1,13) = 2.1, p = 0.166, OP = 0.27F(1,13) = 0.23, p = 0.643, OP = 0.07 1 Correction onsets (extrapolation method) 2 × 2 repeated-measures ANOVA FIXHFIX×H F(1,13) = 70.9, p < 0.001, OP = 1.0F(1,13) = 2.9, p = 0.113, OP = 0.35F(1,13) = 1.0, p = 0.344, OP = 0.15 1 Gaze position 2 × 2×2 repeated-measures ANOVA TWFSHTW×FIXTW×HFIX×H F(1,13) = 14.8, p = 0.002, OP = 0.94F(1,13) = 4.0, p = 0.067, OP = 0.46F(1,13) = 43.9, p < 0.001, OP = 1.0F(1,13) = 16.1, p = 0.001, OP = 0.96F(1,13) = 17.2, p = 0.001, OP = 0.97F(1,13) = 0.09, p = 0.766, OP = 0.06 2 Corrective force differences 2 × 2×2 repeated-measures ANOVA TWTW-OPCTW×TW-OTW×PCTW-O×PC F(1,13) = 99.9, p < 0.001, OP = 1.0F(1,13) = 10.4, p = 0.007, OP = 0.85F(2,26) = 9.7, p = 0.001, OP = 0.97F(1,13) = 19.6, p = 0.001, OP = 0.98F(2,26) = 1.9, p = 0.170, OP = 0.36F(2,26) = 0.5, p = 0.620, OP = 0.12 2 Corrective force differences Planned comparisons nt(nt) vs. nt(wt)wt(nt) vs. wt(wt) p = 0.211, OP = 0.23p < 0.001, OP = 0.99 2 Corrective force differences Pairwise comparisons sp vs. dp-ssp vs. dp-odp-s vs. dp-o p = 0.001, CI [0.06–0.18]p = 0.161, CI [–0.03 to 0.18]p = 0.002, CI [0.08–0.31] 2 Correction onsets (t-test method) One-way ANOVA PC F(2,26) = 0.8, p = 0.441, OP = 0.18 2 Correction onsets (extrapolation method) One-way ANOVA PC F(2,26) = 0.2, p = 0.856, OP = 0.072 2 Corrective force differences at nonperturbed hand One-sample t-tests (corrected α = 0.0125) nt(nt)+spnt(wt)+spwt(nt)+spwt(wt)+sp t(13) = –0.29, p = 0.775, CI [–0.10 to 0.08]t(13) = –0.30, p = 0.767, CI [–0.14 to 0.10]t(13) = –0.23, p = 0.821, CI [–0.13 to 0.10]t(13) = 2.2, p = 0.051, CI [–0.0002 to 0.15] OP, observed power; CI, 95% confidence interval; TW, target width; TW-O, target width, other hand; FS , fixation side; H, hands; PC, perturbation condition; nt/wt, narrow/wide target; fix/nfix, fixation/nonfixation side; sp/dp-s/dp-o, single/double-same/double-opposite perturbation.
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