Add intro section in chapters

2-perception/vhar-system/1-introduction.tex

@@ -1,5 +1,8 @@
-\noindent One approach to render virtual haptic textures consists in simulating the roughness of a periodic grating surface as a vibrotactile sinusoidal.
-The vibrations are rendered to a voice-coil actuator embedded in a hand-held tool or worn on the finger, but to create the illusion of touching a pattern with a fixed spatial period, the frequency of signal must be modulated according to the finger movement (\secref[related_work]{texture_rendering}).
+\section{Introduction}
+\label{intro}
+
+One approach to render virtual haptic textures consists in simulating the roughness of a periodic grating surface as a vibrotactile sinusoidal (\secref[related_work]{texture_rendering}).
+The vibrations are rendered to a voice-coil actuator embedded in a hand-held tool or worn on the finger, but to create the illusion of touching a pattern with a fixed spatial period, the frequency of signal must be modulated according to the finger movement.
 Previous work either used mechanical system to track the movement at high frequency \cite{strohmeier2017generating,friesen2024perceived}, or required the user to move at a constant speed  to keep the signal frequency constant \cite{asano2015vibrotactile,ujitoko2019modulating}.
 However, this method has not yet been integrated in an \AR context, where the user should be able to freely touch and explore the visuo-haptic texture augmentations.
 

2-perception/vhar-textures/1-introduction.tex

@@ -1,4 +1,7 @@
-\noindent When we look at the surface of an everyday object, we then touch it to confirm or contrast our initial visual impression and to estimate the properties of the object, particularly its texture \secref[related_work]{visual_haptic_influence}.
+\section{Introduction}
+\label{intro}
+
+When we look at the surface of an everyday object, we then touch it to confirm or contrast our initial visual impression and to estimate the properties of the object, particularly its texture \secref[related_work]{visual_haptic_influence}.
 Among the various haptic texture augmentations, data-driven methods allow to capture, model and reproduce the roughness perception of real surfaces when touched touched by a hand-held stylus \secref[related_work]{texture_rendering}.
 Databases of visuo-haptic textures have been developed in this way \cite{culbertson2014one,balasubramanian2024sens3}, but they have not yet been explored in an immersive and direct touch context with \AR and wearable haptics.
 

2-perception/xr-perception/1-introduction.tex

@@ -1,4 +1,7 @@
-\noindent Most of the haptic augmentations of tangible surfaces using with wearable haptic devices, including roughness of textures (\secref[related_work]{texture_rendering}), have been studied without a visual feedback, and none have considered the influence of the visual rendering on their perception or integrated them in \AR and \VR (\secref[related_work]{texture_rendering}).
+\section{Introduction}
+\label{intro}
+
+Most of the haptic augmentations of tangible surfaces using with wearable haptic devices, including roughness of textures (\secref[related_work]{texture_rendering}), have been studied without a visual feedback, and none have considered the influence of the visual rendering on their perception or integrated them in \AR and \VR (\secref[related_work]{texture_rendering}).
 Still, it is known that the visual rendering of a tangible can influence the perception of its haptic properties (\secref[related_work]{visual_haptic_influence}), and that the perception of same haptic force-feedback or vibrotactile rendering can differ between \AR and \VR, probably due to difference in perceived simultaneity between visual and haptic stimuli (\secref[related_work]{ar_vr_haptic}).
 Indeed, in \AR, the user can see their own hand touching, the haptic device worn and the \RE, while in \VR they are hidden by the \VE.