65 lines
4.1 KiB
TeX
65 lines
4.1 KiB
TeX
\subsection{Grasp Task}
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\label{grasp}
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\paragraph{Completion Time}
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On the time to complete a trial,
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a \LMM \ANOVA with by-participant random intercepts indicated one statistically significant effect
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of \factor{Target} (\anova{7}{3385}{34.3}, \pinf{0.001})
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but not of \factor{Hand} (\anova{5}{3385}{1.7}, \p{0.1}).
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Targets on the back and the left (\level{B}, \level{LB}, and \level{L}) were slower than targets on the front (\level{LF}, \level{F}, and \level{RF}, \p{0.003}) {except for} \level{RB} (back-right) which was also fast.
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\paragraph{Contacts}
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On the number of contacts,
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a \LMM \ANOVA with by-participant random intercepts indicated two statistically significant effects:
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\factor{Hand} (\anova{5}{3385}{4.9}, \pinf{0.001}, see \figref{results/Grasp-ContactsCount})
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and \factor{Target} (\anova{7}{3385}{20.0}, \pinf{0.001}).
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Fewer contacts were made with \level{Tips} than with \level{None} (\percent{-13}, \p{0.02}) and \level{Occlusion} (\percent{-15}, \p{0.004});
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and less with \level{Mesh} than with \level{None} (\percent{-15}, \p{0.006}) and \level{Occlusion} (\percent{-17}, \p{0.001}).
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This result suggests that having no visible visual hand increased the number of failed grasps or cube drops.
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But, surprisingly, only \level{Tips} and \level{Mesh} were statistically significantly better, not \level{Contour} nor \level{Skeleton}.
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Targets on the back and left were more difficult (\level{B}, \level{LB}, and \level{L}) than targets on the front (\level{LF}, \level{F}, and \level{RF}, \pinf{0.001}).
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\paragraph{Time per Contact}
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On the mean time spent on each contact,
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a \LMM \ANOVA with by-participant random intercepts indicated two statistically significant effects:
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\factor{Hand} (\anova{5}{3385}{9.1}, \pinf{0.001}, see \figref{results/Grasp-MeanContactTime})
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and \factor{Target} (\anova{7}{3385}{5.4}, \pinf{0.001}).
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It was shorter with \level{None} than with \level{Tips} (\percent{-15}, \pinf{0.001}), \level{Skeleton} (\percent{-11}, \p{0.001}) and \level{Mesh} (\percent{-11}, \p{0.001});
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shorter with \level{Occlusion} than with \level{Tips} (\percent{-10}, \pinf{0.001}), \level{Skeleton} (\percent{-8}, \p{0.05}), and \level{Mesh} (\percent{-8}, \p{0.04});
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shorter with \level{Contour} than with \level{Tips} (\percent{-8}, \pinf{0.001}).
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As for the \level{Push} task, the lack of visual hand increased the number of failed grasps or cube drops.
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The \level{Tips} rendering seemed to provide one of the best feedback for the grasping, maybe thanks to the fact that it provides information about both position and rotation of the tracked fingertips.
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This time was the shortest on the front \level{F} than on the other target volumes (\pinf{0.001}).
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\paragraph{Grip Aperture}
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On the average distance between the thumb's fingertip and the other fingertips during grasping,
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a \LMM \ANOVA with by-participant random intercepts and random slopes for \factor{Hand} indicated two statistically significant effects:
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\factor{Hand} (\anova{5}{19}{6.7}, \pinf{0.001}, see \figref{results/Grasp-GripAperture})
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and \factor{Target} (\anova{7}{3270}{4.1}, \pinf{0.001}).
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It was shorter with \level{None} than with \level{Occlusion} (\pinf{0.001}), \level{Contour} (\pinf{0.001}), \level{Skeleton} (\pinf{0.001}) and \level{Mesh} (\pinf{0.001}).
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This result is an evidence of the lack of confidence of participants with no visual hand augmentation: they grasped the cube more to secure it.
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The \response{Grip Aperture} was longer on the right-front (\level{RF}) target volume, indicating a higher confidence, than on back and side targets (\level{R}, \level{RB}, \level{B}, \level{L}, \p{0.03}).
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\begin{subfigs}{grasp_results}{Results of the grasp task performance metrics for each visual hand augmentation.}[
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Geometric means with bootstrap \percent{95} \CI
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and Tukey's \HSD pairwise comparisons: *** is \pinf{0.001}, ** is \pinf{0.01}, and * is \pinf{0.05}.
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][
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\item Number of contacts with the cube.
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\item Time spent on each contact.
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\item Distance between thumb and the other fingertips when grasping.
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]
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\subfig[0.32]{results/Grasp-ContactsCount}
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\subfig[0.32]{results/Grasp-MeanContactTime}
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\subfig[0.32]{results/Grasp-GripAperture}
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\end{subfigs}
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