erwan/phd-thesis
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

Remove comments

Browse Source
This commit is contained in:
Erwan Normand
2025-04-10 16:14:23 +02:00
parent 49c33a5a37
commit 93a47df0f8
4 changed files with 10 additions and 117 deletions
Download Patch File Download Diff File Expand all files Collapse all files

58
2-related-work/4-visuo-haptic-ar.tex
View File

@@ -5,10 +5,7 @@ Perception and manipulation of objects with the hand typically involves both the
Each sense has unique capabilities for perceiving certain object properties, such as color for vision or temperature for touch, but they are equally capable for many properties, such as roughness, hardness, or geometry \cite{baumgartner2013visual}.
Both \AR and wearable haptic systems integrate virtual content into the user's perception as sensory illusions.
It is essential to understand how a visuo-haptic rendering of a virtual object is perceived as a coherent object property, and how wearable haptics have been integrated with immersive \AR.%, especially in immersive \AR where the haptic actuator is moved away so as not to cover the inside of the hand.
% spatial and temporal integration of visuo-haptic feedback as perceptual cues vs proprioception and real touch sensations
% delocalized : not at the point of contact = difficult to integrate with other perceptual cues ?
It is essential to understand how a visuo-haptic rendering of a virtual object is perceived as a coherent object property, and how wearable haptics have been integrated with immersive \AR.
\subsection{Visuo-Haptic Perception of Virtual and Augmented Objects}
\label{vh_perception}
@@ -36,32 +33,23 @@ and the integrated variance $\sigma^2$ is the inverse of the sum of the individu
\end{equation}
This was demonstrated by \textcite{ernst2002humans} in a user study where participants estimated the height of a virtual bar using a fixed-window \OST-\AR display (\secref{ar_displays}) and force-feedback devices worn on the thumb and index finger (\secref{wearability_level}), as shown in \figref{ernst2002humans_setup}.
%They first measured the individual variances of the visual and haptic estimates (\figref{ernst2002humans_within}) and then the combined variance of the visuo-haptic estimates (\figref{ernst2002humans_visuo-haptic}).
On each trial, participants compared the visuo-haptic reference bar (of a fixed height) to a visuo-haptic comparison bar (of a variable height) in a \TIFC task (one bar is tested first, a pause, then the other) and indicated which was taller.
The reference bar had different conflicting visual $s_v$ and haptic $s_h$ heights, and different noise levels were added to the visual feedback to increase its variance.
The objective was to determine a \PSE between the comparison and reference bars, where the participant was equally likely to choose one or the other (\percent{50} of the trials).
%\figref{ernst2002humans_within} shows the discrimination of participants with only the haptic or visual feedback, and how much the estimation becomes difficult (thus higher variance) when noise is added to the visual feedback.
\figref{ernst2004merging_results} shows that when the visual noise was low, the visual feedback had more weight, but as visual noise increased, haptic feedback gained more weight, as predicted by the \MLE model.
\begin{subfigs}{ernst2002humans}{
Visuo-haptic perception of height of a virtual bar \cite{ernst2002humans}.
}[][
\item Experimental setup.%: Participants estimated height visually with an \OST-\AR display and haptically with force-feedback devices worn on the thumb and index fingers.
%\item with only haptic feedback (red) or only visual feedback (blue, with different added noise),
%\item combined visuo-haptic feedback (purple, with different visual noises).
\item Experimental setup.
\item Proportion of trials (vertical axis) where the comparison bar (horizontal axis) was perceived taller than the reference bar as function of increase variance (inverse of reliability) of the visual feedback (colors).
The reference had different conflicting visual $s_v$ and haptic $s_h$ heights.
]
\subfig[.34]{ernst2002humans_setup}
\subfig[.64]{ernst2004merging_results}
%\subfig{ernst2002humans_within}
%\subfig{ernst2002humans_visuo-haptic}
\end{subfigs}
%Hence, the \MLE model explains how a (visual) virtual object in \AR can be perceived as coherent when combined with real haptic sensations of a tangible or a wearable haptic feedback.
The \MLE model implies that when seeing and touching a virtual object in \AR, the combination of visual and haptic stimuli, real or virtual, presented to the user can be perceived as a coherent single object property.
%As long as the user is able to associate the sensations as the same object property, and even if there are discrepancies between the sensations, the overall perception can be influenced by changing one of the stimuli, as discussed in the next sections.
%for example by including tangible objects, wearable haptic feedback, or even by altering the visual rendering of the virtual object, as discussed in the next sections.
\subsubsection{Influence of Visual Rendering on Haptic Perception}
\label{visual_haptic_influence}
@@ -75,7 +63,6 @@ The overall perception can then be modified by changing one of the sensory modal
In a similar setup, but in immersive \VST-\AR, \textcite{kitahara2010sensory} overlaid visual textures on real textured surfaces touched through a glove: many visual textures were found to match the real haptic textures.
\textcite{degraen2019enhancing} and \textcite{gunther2022smooth} also combined multiple virtual objects in \VR with \ThreeD-printed hair structures or with everyday real surfaces, respectively.
They found that the visual perception of roughness and hardness influenced the haptic perception, and that only a few real objects seemed to be sufficient to match all the visual virtual objects (\figref{gunther2022smooth}).
%Taken together, these studies suggest that a set of haptic textures, real or virtual, can be perceived as coherent with a larger set of visual virtual textures.
\fig{gunther2022smooth}{In a passive touch context in \VR, only a smooth and a rough real surfaces were found to match all the visual virtual objects \cite{gunther2022smooth}.}
@@ -93,9 +80,6 @@ For example, in a fixed \VST-\AR screen (\secref{ar_displays}), by visually defo
\subfig{ban2014displaying}
\end{subfigs}
%In all of these studies, the visual expectations of participants influenced their haptic perception.
%In particular, in \AR and \VR, the perception of a haptic rendering or augmentation can be influenced by the visual rendering of the virtual object.
\subsubsection{Perception of Visuo-Haptic Rendering in AR and VR}
\label{ar_vr_haptic}
@@ -116,18 +100,13 @@ Adding a visual delay increased the perceived stiffness of the reference piston,
\subfig[.55]{knorlein2009influence_2}
\end{subfigs}
%explained how these delays affected the integration of the visual and haptic perceptual cues of stiffness.
The stiffness $\tilde{k}(t)$ of the piston is indeed estimated at time $t$ by both sight and proprioception as the ratio of the exerted force $F(t)$ and the displacement $\Delta L(t)$ of the piston, following \eqref{stiffness}, but with potential visual $\Delta t_v$ or haptic $\Delta t_h$ delays.
%\begin{equation}{stiffness_delay}
% \tilde{k}(t) = \frac{F(t + \Delta t_h)}{D(t + \Delta t_v)}
%\end{equation}
Therefore, the perceived stiffness $\tilde{k}(t)$ increases with a haptic delay in force and decreases with a visual delay in displacement \cite{diluca2011effects}.
\textcite{gaffary2017ar} compared perceived stiffness of virtual pistons in \OST-\AR and \VR.
However, the force-feedback device and the participant's hand were not visible (\figref{gaffary2017ar}).
The reference piston was judged to be stiffer when seen in \VR than in \AR, without participants noticing this difference, and more force was exerted on the piston overall in \VR.
This suggests that the haptic stiffness of virtual objects feels \enquote{softer} in an augmented environment than in a full \VE.
%Two differences that could be worth investigating with the two previous studies are the type of \AR (visuo or optical) and to see the hand touching the virtual object.
Finally, \textcite{diluca2019perceptual} investigated the perceived simultaneity of visuo-haptic contact with a virtual object in \VR.
The contact was rendered both by a vibrotactile piezoelectric device on the fingertip and by a visual change in the color of the virtual object.
@@ -162,20 +141,16 @@ Another category of actuators relies on systems that cannot be considered as por
\subsubsection{Nail-Mounted Devices}
\label{vhar_nails}
\textcite{ando2007fingernailmounted} were the first to move the actuator from the fingertip to propose the nail, as described in \secref{texture_rendering}.
\textcite{ando2007fingernailmounted} were the first to move the actuator away from the fingertip.
They proposed to relocate it to the nail instead, as described in \secref{texture_rendering}.
This approach was later extended by \textcite{teng2021touch} with Touch\&Fold, a haptic device able to unfold its end-effector on demand to make contact with the fingertip when touching virtual objects (\figref{teng2021touch_1}).
This moving platform also contains a \LRA (\secref{moving_platforms}) and provides contact pressure and texture sensations.
%The whole system is very compact (\qtyproduct{24 x 24 x 41}{\mm}), lightweight (\qty{9.5}{\g}), and fully portable by including a battery and Bluetooth wireless communication. \qty{20}{\ms} for the Bluetooth
When touching virtual objects in \OST-\AR with the index finger, this device was found to be more realistic overall (5/7) than vibrations with a \LRA at \qty{170}{\Hz} on the nail (3/7).
Still, there is a high (\qty{92}{\ms}) latency for the folding mechanism and this design is not suitable for augmenting real objects.
% teng2021touch: (5.27+3.03+5.23+5.5+5.47)/5 = 4.9
% ando2007fingernailmounted: (2.4+2.63+3.63+2.57+3.2)/5 = 2.9
With Fingeret, \textcite{maeda2022fingeret} adapted the belt actuators (\secref{belt_actuators}) as a \enquote{finger-side actuator} that leaves the fingertip free (\figref{maeda2022fingeret}).
Two rollers, one on each side, can deform the skin: When rotated inward, they pull the skin, simulating a contact sensation, and when rotated outward, they push the skin, simulating a release sensation.
They can also simulate a texture sensation by rapidly rotating in and out.
%The device is also very compact (\qty{60 x 25 x 36}{\mm}), lightweight (\qty{18}{\g}), and portable with a battery and Bluetooth wireless communication with \qty{83}{\ms} latency.
In a user study not in \AR, but directly touching images on a tablet, Fingeret was found to be more realistic (4/7) than a \LRA at \qty{100}{\Hz} on the nail (3/7) for rendering buttons and a patterned texture (\secref{texture_rendering}), but not different from vibrations for rendering high-frequency textures (3.5/7 for both).
However, as with \textcite{teng2021touch}, finger speed was not taken into account when rendering vibrations, which may have been detrimental to texture perception, as described in \secref{texture_rendering}.
@@ -201,9 +176,6 @@ Recall that these devices have also been used to modify the perceived stiffness,
In a \VST-\AR setup, \textcite{scheggi2010shape} explored the effect of rendering the weight of a virtual cube placed on a real surface hold with the thumb, index, and middle fingers (\figref{scheggi2010shape}).
The middle phalanx of each of these fingers was equipped with a haptic ring of \textcite{minamizawa2007gravity}.
%However, no proper user study was conducted to evaluate this feedback.% on the manipulation of the cube.
%that simulated the weight of the cube.
%A virtual cube that could push on the cube was manipulated with the other hand through a force-feedback device.
\textcite{scheggi2010shape} reported that 12 out of 15 participants found the weight haptic feedback essential to feeling the presence of the virtual cube.
In a pick-and-place task in non-immersive \VST-\AR involving direct hand manipulation of both virtual and real objects (\figref{maisto2017evaluation}), \textcite{maisto2017evaluation} and \textcite{meli2018combining} compared the effects of providing haptic or visual feedback about fingertip-object contacts.
@@ -221,31 +193,9 @@ These two studies were also conducted in non-immersive setups, where users viewe
\subfig[.48][m]{maisto2017evaluation}
\end{subfigs}
%\subsubsection{Wrist Bracelet Devices}
%\label{vhar_bracelets}
With their \enquote{Tactile And Squeeze Bracelet Interface} (Tasbi), already mentioned in \secref{belt_actuators}, \textcite{pezent2019tasbi} and \textcite{pezent2022design} explored the use of a wrist-worn bracelet actuator.
It is capable of providing a uniform pressure sensation (up to \qty{15}{\N} and \qty{10}{\Hz}) and vibration with six \LRAs (\qtyrange{150}{200}{\Hz} bandwidth).
A user study was conducted in \VR to compare the perception of visuo-haptic stiffness rendering \cite{pezent2019tasbi}, and showed that the haptic pressure feedback was more important than the visual displacement.
%In a \TIFC task (\secref{sensations_perception}), participants pressed a virtual button with different levels of stiffness via a virtual hand constrained by the \VE (\figref{pezent2019tasbi_2}).
%A higher visual stiffness required a larger physical displacement to press the button (C/D ratio, see \secref{pseudo_haptic}), while the haptic stiffness control the rate of the pressure feedback when pressing.
%When the visual and haptic stiffness were coherent or when only the haptic stiffness changed, participants easily discriminated two buttons with different stiffness levels (\figref{pezent2019tasbi_3}).
%However, if only the visual stiffness changed, participants were not able to discriminate the different stiffness levels (\figref{pezent2019tasbi_4}).
%This suggests that in \VR, the haptic pressure is more important perceptual cue than the visual displacement to render stiffness.
%A short vibration (\qty{25}{\ms} \qty{175}{\Hz} square-wave) was also rendered when contacting the button, but kept constant across all conditions: It may have affected the overall perception when only the visual stiffness changed.
%\begin{subfigs}{pezent2019tasbi}{Visuo-haptic stiffness rendering of a virtual button in \VR with the Tasbi bracelet. }[][
% \item The \VE seen by the user: the virtual hand (in beige) is constrained by the virtual button. The displacement is proportional to the visual stiffness. The real hand (in green) is hidden by the \VE.
% \item When the rendered visuo-haptic stiffness are coherents (in purple) or only the haptic stiffness change (in blue), participants easily discrimated the different levels.
% \item When varying only the visual stiffness (in red) but keeping the haptic stiffness constant, participants were not able to discriminate the different stiffness levels.
% ]
% \subfigsheight{45mm}
% \subfig{pezent2019tasbi_2}
% \subfig{pezent2019tasbi_3}
% \subfig{pezent2019tasbi_4}
%\end{subfigs}
% \cite{sarac2022perceived,palmer2022haptic} not in \AR but studies on relocating to the wrist the haptic feedback of the fingertip-object contacts.
\subsection{Conclusion}
\label{visuo_haptic_conclusion}