\section{Conclusion}
\label{conclusion}

In this chapter, we investigated how users perceived simultaneous and co-localized visuo-haptic texture augmentations of real surfaces seen with an \OST-\AR headset and touched directly with the index finger.
Using the wearable visuo-haptic augmentation system presented in \chapref{vhar_system}, the haptic roughness texture was rendered with on the \HaTT data-driven models and finger speed.
In a user study, 20 participants rated the coherence, realism and perceived roughness of the combination of nine representative visuo-haptic texture pairs.

The results showed that participants consistently identified and matched clusters of visual and haptic textures with similar perceived roughness.
The texture rankings did indeed show that participants perceived the roughness of haptic textures to be very similar.
Conversely, there was less consensus on the perceived roughness of visual textures.
Regarding the final roughness perception ranking of the original visuo-haptic pairs, the haptic roughness sensation dominated the perception.
This suggests that \AR visual textures that augments real surfaces can be enhanced with a set of data-driven vibrotactile haptic textures in a coherent and realistic manner.

This paves the way for new \AR applications capable of augmenting a \RE with virtual visuo-haptic textures, such as visuo-haptic painting in artistic or object design context, or viewing and touching virtual objects in a museum or a showroom.
The latter is illustrated in \figref{experiment/use_case}, where a user applies different visuo-haptic textures to a wall, in an interior design scenario, to compare them visually and by touch.

We instinctively perceive the properties of everyday objects by touching and exploring them, but we essentially interact with them by grasping in order to manipulate them.
In this first part, we focused on the perception of virtual visuo-haptic textures that augment real surfaces when touched with the fingertip.
In the next part, we will propose to improve the direct manipulation with the hand of virtual object with wearable visuo-haptic interaction feedback.

\noindentskip The work described in \chapref{vhar_textures} was presented at the EuroHaptics 2024 conference:

Erwan Normand, Claudio Pacchierotti, Eric Marchand, and Maud Marchal. \enquote{Augmenting the Texture Perception of Tangible Surfaces in Augmented Reality using Vibrotactile Haptic Stimuli}. In: \textit{EuroHaptics}. Lille, France, July 2024. pp. 469--484.

\fig[0.65]{experiment/use_case}{
  Illustration of the texture augmentation in \AR through an interior design scenario.
}[
  A user wearing an \AR headset and a wearable vibrotactile haptic device worn on their index is applying different virtual visuo-haptic textures to a real wall to compare them visually and by touch.
]