\subsection{Discrimination of Vibration Techniques}
\label{technique_results}

Seven participants were able to correctly discriminate between the two vibration techniques, which they described as the contact vibration (being the Impact technique) and the continuous vibration (being the Distance technique) respectively.
%
Seven participants said they only felt differences of intensity with a weak one (being the Impact technique) and a strong one (being the Distance technique).
%
Six participants did not notice the difference between the two vibration techniques.
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There was no evidence that the ability to discriminate the vibration techniques was correlated with the participants' haptic or AR/VR expertise (\pearson{0.4}), nor that it had a statistically significant effect on the performance in the tasks.
%
As the tasks had to be completed as quickly as possible, we hypothesize that little attention was devoted to the different vibration techniques.
%
Indeed, some participants explained that the contact cues were sufficient to indicate whether the cube was being properly pushed or grasped.
%
Although the Distance technique provided additional feedback on the interpenetration of the finger with the cube, it was not strictly necessary to manipulate the cube quickly.


\subsection{Questionnaire}
\label{questions}

\begin{subfigswide}{questions}{%
        Experiment \#2. Boxplots of the questionnaire results of each vibrotactile positioning
        %
        and pairwise Wilcoxon signed-rank tests with Holm-Bonferroni adjustment: *** is \pinf{0.001}, ** is \pinf{0.01}, and * is \pinf{0.05}.
    }
    \subfig[0.24]{results/Question-Vibration Rating-Positioning-Overall}
    \subfig[0.24]{results/Question-Workload-Positioning-Overall}
    \subfig[0.24]{results/Question-Usefulness-Positioning-Overall}
    \subfig[0.24]{results/Question-Realism-Positioning-Overall}
\end{subfigswide}

\figref{questions} shows the questionnaire results for each vibrotactile positioning.
%
Questionnaire results were analyzed using Aligned Rank Transform (ART) non-parametric analysis of variance (\secref{metrics}).
%
Statistically significant effects were further analyzed with post-hoc pairwise comparisons with Holm-Bonferroni adjustment.
%
Wilcoxon signed-rank tests were used for main effects and ART contrasts procedure for interaction effects.
%
Only significant results are reported.


\subsubsection{Vibrotactile Rendering Rating}
\label{vibration_ratings}

There was a main effect of Positioning (\anova{4}{171}{27.0}, \pinf{0.001}).
%
Participants preferred Fingertips more than Wrist (\p{0.01}), Opposite (\pinf{0.001}), and No Vibration (\pinf{0.001});
%
Proximal more than Wrist (\p{0.007}), Opposite (\pinf{0.001}), and No Vibration (\pinf{0.001});
%
And Wrist more than Opposite (\p{0.01}) and No Vibration (\pinf{0.001}).


\subsubsection{Positioning \x Hand Rating}
\label{positioning_hand}

There were two main effects of Positioning (\anova{4}{171}{20.6}, \pinf{0.001}) and of Hand (\anova{1}{171}{12.2}, \pinf{0.001}).
%
Participants preferred Fingertips more than Wrist (\p{0.03}), Opposite (\pinf{0.001}), and No Vibration (\pinf{0.001});
%
Proximal more than Wrist (\p{0.003}), Opposite (\pinf{0.001}), and No Vibration (\pinf{0.001});
%
Wrist more than Opposite (\p{0.03}) and No Vibration (\pinf{0.001});
%
And Skeleton more than No Hand (\pinf{0.001}).


\subsubsection{Workload}
\label{workload}

There was a main of Positioning (\anova{4}{171}{3.9}, \p{0.004}).
%
Participants found Opposite more fatiguing than Fingertips (\p{0.01}), Proximal (\p{0.003}), and Wrist (\p{0.02}).


\subsubsection{Usefulness}
\label{usefulness}

There was a main effect of Positioning (\anova{4}{171}{38.0}, \p{0.041}).
%
Participants found Fingertips the most useful, more than Proximal (\p{0.02}), Wrist (\pinf{0.001}), Opposite (\pinf{0.001}), and No Vibrations (\pinf{0.001});
%
Proximal more than Wrist (\p{0.008}), Opposite (\pinf{0.001}), and No Vibrations (\pinf{0.001});
%
Wrist more than Opposite (\p{0.008}) and No Vibrations (\pinf{0.001});
%
And Opposite more than No Vibrations (\p{0.004}).


\subsubsection{Realism}
\label{realism}

There was a main effect of Positioning (\anova{4}{171}{28.8}, \pinf{0.001}).
%
Participants found Fingertips the most realistic, more than Proximal (\p{0.05}), Wrist (\p{0.004}), Opposite (\pinf{0.001}), and No Vibrations (\pinf{0.001});
%
Proximal more than Wrist (\p{0.03}), Opposite (\pinf{0.001}), and No Vibrations (\pinf{0.001});
%
Wrist more than Opposite (\p{0.03}) and No Vibrations (\pinf{0.001});
%
And Opposite more than No Vibrations (\p{0.03}).
