Face expressions done

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@@ -877,9 +877,35 @@ However, the perceived interruptions were reasonnable.
 
 \subsubsection{Discussion}
 
-Raycursor: issues with convex shapes, long shapes, dense areas.
-
-Emotions: trade-off between isomorphic and non isomorphic
+More than fifty years after the first virtual reality headsets, the use of immersive virtual reality is still in its early stages.
+Social media companies started investing massively on this topic in the last decade with the idea to implement alternative realities that break the barriers of the physical world.
+One of the obvious barriers to break is distance, by allowing people to be in the same room even if they are physically far from each other.
+But when people evolve in such virtual environments, they are free of the constraints of the physical world.
+Therefore when we design interaction techniques to enable people to perform actions in such virtual environments, we also think about ways to perform actions they could not in the physical world.
+The two techniques we discussed in this section allow users to perform two distinct actions: select objects and show a face expressions.
+However they both have in common that they enable users to perform these actions in ways they could not in the physical world.
+In the physical world it is impossible to select an object remotely and show a face expression different from their actual face expression.
+The choice of using these techniques in virtual reality systems is indeed a matter of trade-offs.
+
+Most of the benefits of Raycursor rely on proximity selection.
+The actual benefits of proximity selection was demonstrated with the bubble cursor in both 22 \cite{grossman05} and 3D with a virtual hand \cite{vanacken07}.
+What proximity selection means is that there is always a selectable object, and the area of influence of the targets is a Voronoi diagram.
+The first issue we overlooked in this work is the exact way to interpret the area of influence of 3D objects, as opposed to points.
+We conducted evaluations with spheres and, as a 3D extension to the bubble cursor, the distance to the shpere is the diwtance to the center minus the sphere radius.
+With arbitrary objects, it is unclear which point should be considered.
+This choice has a major effect on the area of influence.
+We identified issues with convex and oblong objects, as well as dense clusters of small objects surrounded by large objects.
+Solutions remain to be investigated for such cases.
+
+The main argument for using a non-isomorphic technique for selecting a face expression is to enable users to show a face expression different to their actual face expression.
+This is typically what we do when we use emojis in messaging or social media apps.
+In particular it allows people to show a specific face expression even if they are not able to perform it at will.
+Not everybody is an actor.
+%What we wanted to evaluate in this work is the ability of people to select face expressions during a conversation without 
+Now, isomorphic techniques also have benefits.
+They do not require a conscious control and they do not disrupt or interrupt a primary task, like talking.
+Moreover, new VR headset already include cameras for this purpose\footnote{\href{https://www.vive.com/eu/accessory/facial-tracker/}{https://www.vive.com/eu/accessory/facial-tracker/}}, which will make it easier to implement such interactions techniques.
+Therefore it would be interesting to investigare the combination of isomorphic and non-isometric techniques to get the best of both, to study the control/automation trade-off.
 
 \section{Conclusion}