Fix vh-hand chapter

3-manipulation/visuo-haptic-hand/2-method.tex

@@ -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.
 %