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Fix vh-hand chapter

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Erwan Normand
2024-09-25 09:00:03 +02:00
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20
3-manipulation/visuo-haptic-hand/1-introduction.tex
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@@ -1,6 +1,20 @@
\section{Introduction}
\label{introduction}
%Providing haptic feedback during free-hand manipulation in \AR is not trivial, as wearing haptic devices on the hand might affect the tracking capabilities of the system.
%Moreover, it is important to leave the user capable of interacting with both virtual and real objects, avoiding the use of haptic interfaces that cover the fingertips or palm.
%For this reason, it is often considered beneficial to move the point of application of the haptic rendering elsewhere on the hand.% (\secref{haptics}).
% Conjointly, a few studies have explored and compared the effects of visual and haptic feedback in tasks involving the manipulation of virtual objects with the hand.
% \textcite{sarac2022perceived} and \textcite{palmer2022haptic} studied the effects of providing haptic feedback about contacts at the fingertips using haptic devices worn at the wrist, testing different mappings.
% Results proved that moving the haptic feedback away from the point(s) of contact is possible and effective, and that its impact is more significant when the visual feedback is limited.
% Results proved that moving the haptic feedback away from the point(s) of contact is possible and effective, and that its impact is more significant when the visual feedback is limited.
%A final question is whether one or the other of these (haptic or visual) hand renderings should be preferred \cite{maisto2017evaluation, meli2018combining}, or whether a combined visuo-haptic rendering is beneficial for users.
%In fact, both hand renderings can provide sufficient sensory cues for efficient manipulation of virtual objects in \AR, or conversely, they can be shown to be complementary.
The contributions of this chapter are:
\begin{itemize}
\item The evaluation in a user study with 20 participants of the effect of providing a vibrotactile feedback of the fingertip contacts with \VOs, during direct manipulation with bare hand in \AR, at four different delocalized positionings of the haptic rendering on the hand and with two contact vibration techniques.
\item The comparison of these vibrotactile positionings and renderings techniques with the two most representative visual renderings of the hand established in the \chapref{visual_hand}.
\end{itemize}
\fig[0.6]{method/locations}{Setup of the vibrotactile positionings on the hand. }{
To ensure minimal encumbrance, we used the same two motors throughout the experiment, moving them to the considered positioning before each new experimental block (in this case, on the co-located proximal phalanges, \emph{Prox}).
Thin self-gripping straps were placed on the five considered positionings during the entirety of the experiment.
}

82
3-manipulation/visuo-haptic-hand/2-method.tex
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@@ -1,70 +1,52 @@
\section{User Study}
\label{method}
Providing haptic feedback during free-hand manipulation in \AR is not trivial, as wearing haptic devices on the hand might affect the tracking capabilities of the system.
%
Moreover, it is important to leave the user capable of interacting with both virtual and real objects, avoiding the use of haptic interfaces that cover the fingertips or palm.
%
For this reason, it is often considered beneficial to move the point of application of the haptic rendering elsewhere on the hand.% (\secref{haptics}).
This second experiment aims to evaluate whether a visuo-haptic hand rendering affects the performance and user experience of manipulation of virtual objects with bare hands in \AR.
%
The chosen visuo-haptic hand renderings are the combination of the two most representative visual hand renderings established in the first experiment, \ie Skeleton and None, described in \secref[visual_hand]{hands}, with two contact vibration techniques provided at four delocalized positions on the hand.
\subsection{Vibrotactile Renderings}
\section{Vibrotactile Renderings of the Hand-Object Contacts}
\label{vibration}
The vibrotactile hand rendering provided information about the contacts between the virtual object and the thumb and index fingers of the user, as they were the two fingers most used for grasping in our first experiment.
%
The vibrotactile hand rendering provided information about the contacts between the \VO and the thumb and index fingers of the user, as they are the two fingers most used for grasping (\secref[related_work]{grasp_types}).
We evaluated both the delocalized positioning and the contact vibration technique of the vibrotactile hand rendering.
\subsubsection{Vibrotactile Positionings}
\subsection{Vibrotactile Positionings}
\label{positioning}
\fig[0.30]{method/locations}{%
Experiment \#2: setup of the vibrotactile devices.
%
To ensure minimal encumbrance, we used the same two motors throughout the experiment, moving them to the considered positioning before each new experimental block (in this case, on the co-located proximal phalanges, \emph{Prox}).
%
Thin self-gripping straps were placed on the five considered positionings during the entirety of the experiment.
}
We considered five different positionings for providing the vibrotactile rendering as feedback of the contacts between the virtual hand and the \VO, as shown in \figref{method/locations}.
They are representative of the most common locations used by wearable haptic devices in \AR to place their end-effector, as found in the literature (\secref[related_work]{vhar_haptics}), as well as other positionings that have been employed for manipulation tasks.
For each positioning, we used two vibrating actuators, for the thumb and index finger, respectively.
They are described as follows, with the corresponding abbreviation in parentheses:
\begin{itemize}
\item \textit{Fingertips (Tips):} Vibrating actuators were placed right above the nails, similarly to \cite{ando2007fingernailmounted}. This is the positioning closest to the fingertips.
%
\item \textit{Proximal Phalanges (Prox):} Vibrating actuators were placed on the dorsal side of the proximal phalanges, similarly to \cite{maisto2017evaluation, meli2018combining, chinello2020modular}.
%
\item \textit{Wrist (Wris):} Vibrating actuators providing contacts rendering for the index and thumb were placed on ulnar and radial sides of the wrist, similarly to \cite{pezent2019tasbi, palmer2022haptic, sarac2022perceived}.
%
\item \textit{Opposite fingertips (Oppo):} Vibrating actuators were placed on the fingertips of contralateral hand, also above the nails, similarly to \cite{prattichizzo2012cutaneous, detinguy2018enhancing}.
%
\item \textit{Nowhere (Nowh):} As a reference, we also considered the case where we provided no vibrotactile rendering.
\item \level{Fingertips} (Tips): Vibrating actuators were placed right above the nails, similarly to \cite{ando2007fingernailmounted}. This is the positioning closest to the fingertips.
\item \level{Proximal} Phalanges (Prox): Vibrating actuators were placed on the dorsal side of the proximal phalanges, similarly to \cite{maisto2017evaluation,meli2018combining,chinello2020modular}.
\item \level{Wrist} (Wris): Vibrating actuators providing contacts rendering for the index and thumb were placed on ulnar and radial sides of the wrist, similarly to \cite{pezent2019tasbi,palmer2022haptic,sarac2022perceived}.
\item \level{Opposite} Fingertips (Oppo): Vibrating actuators were placed on the fingertips of contralateral hand, also above the nails, similarly to \cite{prattichizzo2012cutaneous,detinguy2018enhancing}.
\item \level{Nowhere} (Nowh): As a reference, we also considered the case where we provided no vibrotactile rendering, as in \chapref{visual_hand}.
\end{itemize}
\subsubsection{Contact Vibration Techniques}
\subsection{Contact Vibration Techniques}
\label{technique}
When a fingertip contacts the virtual cube, we activate the corresponding vibrating actuator.
%
We considered two representative contact vibration techniques, \ie two ways of rendering such contacts through vibrations:
%
\begin{itemize}
\item \textit{Impact (Impa):} a \qty{200}{\ms}--long vibration burst is applied when the fingertip makes contact with the object; the amplitude of the vibration is proportional to the speed of the fingertip at the moment of the contact.
\item \textit{Distance (Dist):} a continuous vibration is applied whenever the fingertip is in contact with the object; the amplitude of the vibration is proportional to the interpenetration between the fingertip and the virtual cube surface.
\item \level{Impact} (Impa): a \qty{200}{\ms}--long vibration burst is applied when the fingertip makes contact with the object.
The amplitude of the vibration is proportional to the speed of the fingertip at the moment of the contact.
This technique is inspired by the impact vibrations modelled by tapping on real surfaces, as described in \secref[related_work]{hardness_rendering}.
\item \level{Distance} (Dist): a continuous vibration is applied whenever the fingertip is in contact with the object.
The amplitude of the vibration is proportional to the interpenetration between the fingertip and the virtual cube surface.
\end{itemize}
%
The implementation of these two techniques have been tuned according to the results of a preliminary experiment.
%
Three participants were asked to carry out a series of push and grasp tasks similar to those used in the actual experiment.
%
Results showed that 95~\% of the contacts between the fingertip and the virtual cube happened at speeds below \qty{1.5}{\m\per\s}.
%
We also measured the perceived minimum amplitude to be 15~\% (\qty{0.6}{\g}) of the maximum amplitude of the motors we used.
%
For this reason, we designed the Impact vibration technique (Impa) so that contact speeds from \qtyrange{0}{1.5}{\m\per\s} are linearly mapped into \qtyrange{15}{100}{\%} amplitude commands for the motors.
%
Similarly, we designed the distance vibration technique (Dist) so that interpenetrations from \qtyrange{0}{2.5}{\cm} are linearly mapped into \qtyrange{15}{100}{\%} amplitude commands for the motors, recalling that the virtual cube has an edge of \qty{5}{\cm}.
\section{User Study}
\label{method}
This user study aims to evaluate whether a visuo-haptic hand rendering affects the user performance and experience of manipulation of \VOs with bare hands in \OST-\AR.
The chosen visuo-haptic hand renderings are the combination of the two most representative visual hand renderings established in the first experiment, \ie \level{Skeleton} and \level{None}, described in \secref[visual_hand]{hands}, with the two contact vibration techniques provided at the four delocalized positions on the hand described in \secref{vibration}.
\subsection{Experimental Design}
\label{design}
@@ -94,20 +76,18 @@ Similarly, we designed the distance vibration technique (Dist) so that interpene
\subfig[0.24]{results/Push-TimePerContact-Hand-Overall-Means}
\end{subfigs}
We considered the same two tasks as in Experiment \#1, described in \secref[visual_hand]{tasks}, that we analyzed separately, considering four independent, within-subject variables:
We considered the same two tasks as described in \secref[visual_hand]{tasks}, that we analyzed separately, considering four independent, within-subject variables:
\begin{itemize}
\item \emph{{Vibrotactile Positioning}:} the five positionings for providing vibrotactile hand rendering of the virtual contacts, as described in \secref{positioning}.
\item \emph{Contact Vibration Technique}: the two contact vibration techniques, as described in \secref{technique}.
\item \emph{visual Hand rendering}: two visual hand renderings from the first experiment, Skeleton (Skel) and None, as described in \secref[visual_hand]{hands}; we considered Skeleton as it performed the best in terms of performance and perceived effectiveness and None as reference.
\item \emph{Target}: we considered target volumes located at NW and SW during the Push task, and at NE, NW, SW, and SE during the Grasp task (\figref{tasks}); we considered these targets because they presented different difficulties.
\item \emph{visual Hand rendering}: two visual hand renderings from the first experiment, \level{Skeleton} (Skel) and \level{None}, as described in \secref[visual_hand]{hands}; we considered \level{Skeleton} as it performed the best in terms of performance and perceived effectiveness and \level{None} as reference.
\item \emph{Target}: we considered target volumes located at \level{LB} and \level{LF} during the \factor{Push} task, and at \level{RB}, \level{LB}, \level{LF}, and \level{RF} during the \factor{Grasp} task (\figref{tasks}); we considered these targets because they presented different difficulties.
\end{itemize}
To account for learning and fatigue effects, the positioning of the vibrotactile hand rendering (positioning) was counter-balanced using a balanced \numproduct{10 x 10} Latin square.
%
In these ten blocks, all possible Technique \x Hand \x Target combination conditions were repeated three times in a random order.
%
As we did not find any relevant effect of the order in which the tasks were performed in the first experiment, we fixed the order of the tasks: first, the Push task and then the Grasp task.
As we did not find any relevant effect of the order in which the tasks were performed in the first experiment, we fixed the order of the tasks: first, the \factor{Push} task and then the \factor{Grasp} task.
This design led to a total of 5 vibrotactile positionings \x 2 vibration contact techniques \x 2 visual hand rendering \x (2 targets on the Push task + 4 targets on the Grasp task) \x 3 repetitions $=$ 420 trials per participant.
@@ -155,7 +135,7 @@ When a phalanx collider of the tracked hand contacts the virtual cube,
%
a spring with a low stiffness is created and attached between the cube and the collider.
%
The spring pulls gently the cube toward the phalanxes in contact with the object so as to help maintain a natural and stable grasp.
The spring pulls gently the cube toward the phalanxes in contact with the object to help maintain a natural and stable grasp.
%
When the contact is lost, the spring is destroyed.
%

18
3-manipulation/visuo-haptic-hand/3-1-push.tex
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@@ -8,13 +8,13 @@ On the time to complete a trial, there were two statistically significant effect
Positioning (\anova{4}{1990}{3.8}, \p{0.004}, see \figref{results/Push-CompletionTime-Location-Overall-Means}) %
and Target (\anova{1}{1990}{3.9}, \p{0.05}).
%
Fingertips was slower than Proximal (\qty{+11}{\%}, \p{0.01}) or Opposite (\qty{+12}{\%}, \p{0.03}).
\level{Fingertips} was slower than \level{Proximal} (\qty{+11}{\%}, \p{0.01}) or \level{Opposite} (\qty{+12}{\%}, \p{0.03}).
%
There was no evidence of an advantage of Proximal or Opposite on No Vibrations, nor a disadvantage of Fingertips on No Vibrations.
There was no evidence of an advantage of \level{Proximal} or \level{Opposite} on \level{Nowhere}, nor a disadvantage of \level{Fingertips} on \level{Nowhere}.
%
Yet, there was a tendency of faster trials with Proximal and Opposite.
Yet, there was a tendency of faster trials with \level{Proximal} and \level{Opposite}.
%
The NW target volume was also faster than the SW (\p{0.05}).
The \level{LB} target volume was also faster than the \level{LF} (\p{0.05}).
\subsubsection{Contacts}
\label{push_contacts_count}
@@ -22,7 +22,7 @@ The NW target volume was also faster than the SW (\p{0.05}).
On the number of contacts, there was one statistically significant effect of %
Positioning (\anova{4}{1990}{2.4}, \p{0.05}, see \figref{results/Push-Contacts-Location-Overall-Means}).
%
More contacts were made with Fingertips than with Opposite (\qty{+12}{\%}, \p{0.03}).
More contacts were made with \level{Fingertips} than with \level{Opposite} (\qty{+12}{\%}, \p{0.03}).
%
This could indicate more difficulties to adjust the virtual cube inside the target volume.
@@ -34,12 +34,12 @@ Positioning (\anova{4}{1990}{11.5}, \pinf{0.001}, see \figref{results/Push-TimeP
and of Hand (\anova{1}{1990}{16.1}, \pinf{0.001}, see \figref{results/Push-TimePerContact-Hand-Overall-Means})%
but not of the Positioning \x Hand interaction.
%
It was shorter with Fingertips than with Wrist (\qty{-15}{\%}, \pinf{0.001}), Opposite (\qty{-11}{\%}, \p{0.01}), or NoVi (\qty{-15}{\%}, \pinf{0.001});
It was shorter with \level{Fingertips} than with \level{Wrist} (\qty{-15}{\%}, \pinf{0.001}), \level{Opposite} (\qty{-11}{\%}, \p{0.01}), or NoVi (\qty{-15}{\%}, \pinf{0.001});
%
and shorter with Proximal than with Wrist (\qty{-16}{\%}, \pinf{0.001}), Opposite (\qty{-12}{\%}, \p{0.005}), or No Vibrations (\qty{-16}{\%}, \pinf{0.001}).
and shorter with \level{Proximal} than with \level{Wrist} (\qty{-16}{\%}, \pinf{0.001}), \level{Opposite} (\qty{-12}{\%}, \p{0.005}), or \level{Nowhere} (\qty{-16}{\%}, \pinf{0.001}).
%
This showed different strategies to adjust the cube inside the target volume, with faster repeated pushes with the Fingertips and Proximal positionings.
This showed different strategies to adjust the cube inside the target volume, with faster repeated pushes with the \level{Fingertips} and \level{Proximal} positionings.
%
It was also shorter with None than with Skeleton (\qty{-9}{\%}, \pinf{0.001}).
It was also shorter with \level{None} than with \level{Skeleton} (\qty{-9}{\%}, \pinf{0.001}).
%
This indicates, as for the first experiment, more confidence with a visual hand rendering.

31
3-manipulation/visuo-haptic-hand/3-2-grasp.tex
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@@ -8,14 +8,13 @@ On the time to complete a trial, there were two statistically significant effect
Positioning (\anova{4}{3990}{13.6}, \pinf{0.001}, see \figref{results/Grasp-CompletionTime-Location-Overall-Means}) %
and Target (\anova{3}{3990}{18.8}, \pinf{0.001}).
%
Opposite was faster than Fingertips (\qty{+19}{\%}, \pinf{0.001}), Proximal (\qty{+13}{\%}, \pinf{0.001}), Wrist (\qty{+14}{\%}, \pinf{0.001}), and No Vibrations (\qty{+8}{\%}, \p{0.03}).
\level{\level{Opposite}} was faster than \level{Fingertips} (\qty{+19}{\%}, \pinf{0.001}), \level{Proximal} (\qty{+13}{\%}, \pinf{0.001}), \level{Wrist} (\qty{+14}{\%}, \pinf{0.001}), and \level{Nowhere} (\qty{+8}{\%}, \p{0.03}).
%
No Vibrations was faster than Fingertips (\qty{+11}{\%}, \pinf{0.001}).
\level{Nowhere} was faster than \level{Fingertips} (\qty{+11}{\%}, \pinf{0.001}).
%
SE was faster than NE (\pinf{0.001}), NW (\pinf{0.001}), and SW (\pinf{0.001});
\level{RF} was faster than \level{RB} (\pinf{0.001}), \level{LB} (\pinf{0.001}), and \level{LF} (\pinf{0.001});
%
and SW was faster than NE (\p{0.03}).
and \level{LF} was faster than \level{RB} (\p{0.03}).
\subsubsection{Contacts}
\label{grasp_contacts_count}
@@ -24,12 +23,11 @@ On the number of contacts, there were two statistically significant effects: %
Positioning (\anova{4}{3990}{15.1}, \pinf{0.001}, see \figref{results/Grasp-Contacts-Location-Overall-Means}) %
and Target (\anova{3}{3990}{7.6}, \pinf{0.001}).
%
Fewer contacts were made with Opposite than with Fingertips (\qty{-26}{\%}, \pinf{0.001}), Proximal (\qty{-17}{\%}, \pinf{0.001}), or Wrist (\qty{-12}{\%}, \p{0.002});
Fewer contacts were made with \level{Opposite} than with \level{Fingertips} (\qty{-26}{\%}, \pinf{0.001}), \level{Proximal} (\qty{-17}{\%}, \pinf{0.001}), or \level{Wrist} (\qty{-12}{\%}, \p{0.002});
%
but more with Fingertips than with Wrist (\qty{+13}{\%}, \p{0.002}) or No Vibrations (\qty{+17}{\%}, \pinf{0.001}).
but more with \level{Fingertips} than with \level{Wrist} (\qty{+13}{\%}, \p{0.002}) or \level{Nowhere} (\qty{+17}{\%}, \pinf{0.001}).
%
It was also easier on SW than on NE (\pinf{0.001}), NW (\p{0.006}), or SE (\p{0.03}).
It was also easier on \level{LF} than on \level{RB} (\pinf{0.001}), \level{LB} (\p{0.006}), or \level{RF} (\p{0.03}).
\subsubsection{Time per Contact}
\label{grasp_time_per_contact}
@@ -38,12 +36,11 @@ On the mean time spent on each contact, there were two statistically significant
Positioning (\anova{4}{3990}{2.9}, \p{0.02}, see \figref{results/Grasp-TimePerContact-Location-Overall-Means}) %
and Target (\anova{3}{3990}{62.6}, \pinf{0.001}).
%
It was shorter with Fingertips than with Opposite (\qty{+7}{\%}, \p{0.01}).
It was shorter with \level{Fingertips} than with \level{Opposite} (\qty{+7}{\%}, \p{0.01}).
%
It was also shorter on SE than on NE, NW or SW (\pinf{0.001});
It was also shorter on \level{RF} than on \level{RB}, \level{LB} or \level{LF} (\pinf{0.001});
%
but longer on SW than on NE or NW (\pinf{0.001}).
but longer on \level{LF} than on \level{RB} or \level{LB} (\pinf{0.001}).
\subsubsection{Grip Aperture}
\label{grasp_grip_aperture}
@@ -53,10 +50,10 @@ statistically significant effects: %
Positioning (\anova{4}{3990}{30.1}, \pinf{0.001}, see \figref{results/Grasp-GripAperture-Location-Overall-Means}) %
and Target (\anova{3}{3990}{19.9}, \pinf{0.001}).
%
It was longer with Fingertips than with Proximal (\pinf{0.001}), Wrist (\pinf{0.001}), Opposite (\pinf{0.001}), or No Vibrations (\pinf{0.001});
It was longer with \level{Fingertips} than with \level{Proximal} (\pinf{0.001}), \level{Wrist} (\pinf{0.001}), \level{Opposite} (\pinf{0.001}), or \level{Nowhere} (\pinf{0.001});
%
and longer with Proximal than with Wrist (\pinf{0.001}) or No Vibrations (\pinf{0.001}).
and longer with \level{Proximal} than with \level{Wrist} (\pinf{0.001}) or \level{Nowhere} (\pinf{0.001}).
%
But, it was shorter with NE than with NW or SW (\pinf{0.001});
But, it was shorter with \level{RB} than with \level{LB} or \level{LF} (\pinf{0.001});
%
and shorter with SE than with NW or SW (\pinf{0.001}).
and shorter with \level{RF} than with \level{LB} or \level{LF} (\pinf{0.001}).

38
3-manipulation/visuo-haptic-hand/3-3-questions.tex
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@@ -1,9 +1,9 @@
\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 were able to correctly discriminate between the two vibration techniques, which they described as the contact vibration (being the \level{Impact} technique) and the continuous vibration (being the \level{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).
Seven participants said they only felt differences of intensity with a weak one (being the \level{Impact} technique) and a strong one (being the \level{Distance} technique).
%
Six participants did not notice the difference between the two vibration techniques.
%
@@ -13,7 +13,7 @@ As the tasks had to be completed as quickly as possible, we hypothesize that lit
%
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.
Although the \level{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}
@@ -44,54 +44,54 @@ Only significant results are reported.
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});
Participants preferred \level{Fingertips} more than \level{Wrist} (\p{0.01}), \level{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});
\level{Proximal} more than \level{Wrist} (\p{0.007}), \level{Opposite} (\pinf{0.001}), and No Vibration (\pinf{0.001});
%
And Wrist more than Opposite (\p{0.01}) and No Vibration (\pinf{0.001}).
And \level{Wrist} more than \level{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});
Participants preferred \level{Fingertips} more than \level{Wrist} (\p{0.03}), \level{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});
\level{Proximal} more than \level{Wrist} (\p{0.003}), \level{Opposite} (\pinf{0.001}), and No Vibration (\pinf{0.001});
%
Wrist more than Opposite (\p{0.03}) and No Vibration (\pinf{0.001});
\level{Wrist} more than \level{Opposite} (\p{0.03}) and No Vibration (\pinf{0.001});
%
And Skeleton more than No Hand (\pinf{0.001}).
And \level{Skeleton} more than No Hand (\pinf{0.001}).
\subsubsection{Workload}
\label{workload}
There was a main effect 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}).
Participants found \level{Opposite} more fatiguing than \level{Fingertips} (\p{0.01}), \level{Proximal} (\p{0.003}), and \level{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});
Participants found \level{Fingertips} the most useful, more than \level{Proximal} (\p{0.02}), \level{Wrist} (\pinf{0.001}), \level{Opposite} (\pinf{0.001}), and \level{Nowhere} (\pinf{0.001});
%
Proximal more than Wrist (\p{0.008}), Opposite (\pinf{0.001}), and No Vibrations (\pinf{0.001});
\level{Proximal} more than \level{Wrist} (\p{0.008}), \level{Opposite} (\pinf{0.001}), and \level{Nowhere} (\pinf{0.001});
%
Wrist more than Opposite (\p{0.008}) and No Vibrations (\pinf{0.001});
\level{Wrist} more than \level{Opposite} (\p{0.008}) and \level{Nowhere} (\pinf{0.001});
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And Opposite more than No Vibrations (\p{0.004}).
And \level{Opposite} more than \level{Nowhere} (\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});
Participants found \level{Fingertips} the most realistic, more than \level{Proximal} (\p{0.05}), \level{Wrist} (\p{0.004}), \level{Opposite} (\pinf{0.001}), and \level{Nowhere} (\pinf{0.001});
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Proximal more than Wrist (\p{0.03}), Opposite (\pinf{0.001}), and No Vibrations (\pinf{0.001});
\level{Proximal} more than \level{Wrist} (\p{0.03}), \level{Opposite} (\pinf{0.001}), and \level{Nowhere} (\pinf{0.001});
%
Wrist more than Opposite (\p{0.03}) and No Vibrations (\pinf{0.001});
\level{Wrist} more than \level{Opposite} (\p{0.03}) and \level{Nowhere} (\pinf{0.001});
%
And Opposite more than No Vibrations (\p{0.03}).
And \level{Opposite} more than \level{Nowhere} (\p{0.03}).

2
3-manipulation/visuo-haptic-hand/3-results.tex
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@@ -7,7 +7,7 @@
\item Time to complete a trial.
\item Number of contacts with the cube.
\item Time spent on each contact.
\item Distance between thumb and the other fingertips when grasping.
\item \level{Distance} between thumb and the other fingertips when grasping.
]
\subfig[0.24]{results/Grasp-CompletionTime-Location-Overall-Means}
\subfig[0.24]{results/Grasp-Contacts-Location-Overall-Means}

26
3-manipulation/visuo-haptic-hand/4-discussion.tex
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@@ -3,7 +3,7 @@
We evaluated sixteen visuo-haptic renderings of the hand, in the same two virtual object manipulation tasks in \AR as in the first experiment, as the combination of two vibrotactile contact techniques provided at four delocalized positions on the hand with the two most representative visual hand renderings established in the first experiment.
In the Push task, vibrotactile haptic hand rendering has been proven beneficial with the Proximal positioning, which registered a low completion time, but detrimental with the Fingertips positioning, which performed worse (\figref{results/Push-CompletionTime-Location-Overall-Means}) than the Proximal and Opposite (on the contralateral hand) positionings.
In the \factor{Push} task, vibrotactile haptic hand rendering has been proven beneficial with the \level{Proximal} positioning, which registered a low completion time, but detrimental with the \level{Fingertips} positioning, which performed worse (\figref{results/Push-CompletionTime-Location-Overall-Means}) than the \level{Proximal} and \level{Opposite} (on the contralateral hand) positionings.
%
The cause might be the intensity of vibrations, which many participants found rather strong and possibly distracting when provided at the fingertips.
%
@@ -13,19 +13,19 @@ Another reason could be the visual impairment caused by the vibrotactile motors
We observed different strategies than in the first experiment for the two tasks.
%
During the Push task, participants made more and shorter contacts to adjust the cube inside the target volume (\figref{results/Push-Contacts-Location-Overall-Means} and \figref{results/Push-TimePerContact-Location-Overall-Means}).
During the \factor{Push} task, participants made more and shorter contacts to adjust the cube inside the target volume (\figref{results/Push-Contacts-Location-Overall-Means} and \figref{results/Push-TimePerContact-Location-Overall-Means}).
%
During the Grasp task, participants pressed the cube 25~\% harder on average (\figref{results/Grasp-GripAperture-Location-Overall-Means}).
During the \factor{Grasp} task, participants pressed the cube 25~\% harder on average (\figref{results/Grasp-GripAperture-Location-Overall-Means}).
%
The Fingertips and Proximal positionings led to a slightly larger grip aperture than the others.
The \level{Fingertips} and \level{Proximal} positionings led to a slightly larger grip aperture than the others.
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We think that the proximity of the vibrotactile rendering to the point of contact made users to take more time to adjust their grip in a more realistic manner, \ie closer to the surface of the cube.
%
This could also be the cause of the higher number of failed grasps or cube drops: indeed, we observed that the larger the grip aperture, the higher the number of contacts.
%
Consequently, the Fingertips positioning was slower (\figref{results/Grasp-CompletionTime-Location-Overall-Means}) and more prone to error (\figref{results/Grasp-Contacts-Location-Overall-Means}) than the Opposite and Nowhere positionings.
Consequently, the \level{Fingertips} positioning was slower (\figref{results/Grasp-CompletionTime-Location-Overall-Means}) and more prone to error (\figref{results/Grasp-Contacts-Location-Overall-Means}) than the \level{Opposite} and \level{Nowhere} positionings.
In both tasks, the Opposite positioning also seemed to be faster (\figref{results/Push-CompletionTime-Location-Overall-Means}) than having no vibrotactile hand rendering (Nowhere positioning).
In both tasks, the \level{Opposite} positioning also seemed to be faster (\figref{results/Push-CompletionTime-Location-Overall-Means}) than having no vibrotactile hand rendering (\level{Nowhere} positioning).
%
However, participants also felt more workload (\figref{questions}) with this positioning opposite to the site of the interaction.
%
@@ -35,17 +35,17 @@ Overall, many participants appreciated the vibrotactile hand renderings, comment
%
However, the closer to the contact point, the better the vibrotactile rendering was perceived (\figref{questions}).
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This seemed inversely correlated with the performance, except for the Nowhere positioning, \eg both the Fingertips and Proximal positionings were perceived as more effective, useful, and realistic than the other positionings despite lower performance.
This seemed inversely correlated with the performance, except for the \level{Nowhere} positioning, \eg both the \level{Fingertips} and \level{Proximal} positionings were perceived as more effective, useful, and realistic than the other positionings despite lower performance.
Considering the two tasks, no clear difference in performance or appreciation was found between the two contact vibration techniques.
%
While the majority of participants discriminated the two different techniques, only a minority identified them correctly (\secref{technique_results}).
%
It seemed that the Impact technique was sufficient to provide contact information compared to the Distance technique, which provided additional feedback on interpenetration, as reported by participants.
It seemed that the Impact technique was sufficient to provide contact information compared to the \level{Distance} technique, which provided additional feedback on interpenetration, as reported by participants.
No difference in performance was found between the two visual hand renderings, except for the Push task, where the Skeleton hand rendering resulted again in longer contacts.
No difference in performance was found between the two visual hand renderings, except for the \factor{Push} task, where the \level{Skeleton} hand rendering resulted again in longer contacts.
%
Additionally, the Skeleton rendering was appreciated and perceived as more effective than having no visual hand rendering, confirming the results of our first experiment.
Additionally, the \level{Skeleton} rendering was appreciated and perceived as more effective than having no visual hand rendering, confirming the results of our first experiment.
%
Participants reported that this visual hand rendering provided good feedback on the status of the hand tracking while being constrained to the cube, and helped with rotation adjustment in both tasks.
%
@@ -55,9 +55,9 @@ Indeed, receiving a vibrotactile hand rendering was found by participants as a m
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This result suggests that providing a visual hand rendering may not be useful during the grasping phase, but may be beneficial prior to contact with the virtual object and during position and rotation adjustment, providing valuable information about the hand pose.
%
It is also worth noting that the improved hand tracking and grasp helper improved the manipulation of the cube with respect to the first experiment, as shown by the shorter completion time during the Grasp task.
It is also worth noting that the improved hand tracking and grasp helper improved the manipulation of the cube with respect to the first experiment, as shown by the shorter completion time during the \factor{Grasp} task.
%
This improvement could also be the reason for the smaller differences between the Skeleton and the None visual hand renderings in this second experiment.
This improvement could also be the reason for the smaller differences between the \level{Skeleton} and the \level{None} visual hand renderings in this second experiment.
In summary, the positioning of the vibrotactile haptic rendering of the hand affected on the performance and experience of users manipulating virtual objects with their bare hands in \AR.
%
@@ -75,7 +75,7 @@ This behavior has likely given them a better experience of the tasks and more co
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On the other hand, the unfamiliarity of the contralateral hand positioning caused participants to spend more time understanding the haptic stimuli, which might have made them more focused on performing the task.
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In terms of the contact vibration technique, the continuous vibration technique on the finger interpenetration (Distance technique) did not make a difference to performance, although it provided more information.
In terms of the contact vibration technique, the continuous vibration technique on the finger interpenetration (\level{Distance} technique) did not make a difference to performance, although it provided more information.
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Participants felt that vibration bursts were sufficient (Impact technique) to confirm contact with the virtual object.
%