\section{Conclusion}
\label{conclusion}

In this chapter, we studied how the perception of wearable haptic augmented textures is affected by the visual feedback of the virtual hand and the environment, being either real, augmented or virtual.
Using the wearable visuo-haptic augmentation system presented in \chapref{vhar_system}, we augmented the perceived roughness of real surfaces with virtual vibrotactile textures rendered on the finger.
With an \OST-\AR headset, that could be switched to a \VR only view, we considered three visual rendering conditions: (1) without visual augmentation, (2) with a realistic virtual hand rendering in \AR, and (3) with the same virtual hand in \VR.
We then evaluated the perceived roughness augmentation in these three visual conditions with a psychophysical user study involving 20 participants and extensive questionnaires.

Our results showed that the visual virtuality of the hand (real or virtual) and the environment (\AR or \VR) had a significant effect on the perception of haptic textures and the exploration behaviour of the participants.
The textures were on average perceived as \enquote{rougher} when touched with the real hand alone than with a virtual hand either in \AR, with \VR in between.
Similarly, the sensitivity to differences in roughness was better with the real hand, less good with \AR, and in between with \VR.
Exploration behaviour was also slower in \VR than with real hand alone, although subjective evaluation of the texture was not affected.
We hypothesized that this difference in perception was due to the \emph{perceived latency} between the finger movements and the different visual, haptic and proprioceptive feedbacks, which were the same in all visual renderings, but were more noticeable in \AR and \VR than without visual augmentation.

This study suggests that attention should be paid to the respective latencies of the visual and haptic sensory feedbacks inherent in such systems and, more importantly, to \emph{the perception of their possible asynchrony}.
Latencies should be measured \cite{friston2014measuring}, minimized to an acceptable level for users and kept synchronized with each other \cite{diluca2019perceptual}.
It seems also that the visual aspect of the hand or the environment on itself has little effect on the perception of haptic feedback, but the degree of visual virtuality can affect the asynchrony perception of the latencies, even though the latencies remain identical.
When designing for wearable haptics or integrating it into \AR/\VR, it seems important to test its perception in real (\RE), augmented (\AE) and virtual (\VE) environments.

In the next chapter we present a second user study where we investigate the perception of simultaneous and co-localised visual and haptic texture augmentation.
We will use the same system presented in \chapref{vhar_system} and a visual rendering condition similar to the \level{Real} condition of this study, in \AR without the virtual hand overlay.

\noindentskip The work described in \chapref{vhar_system} and \ref{xr_perception} was presented at the VRST 2024 conference:

Erwan Normand, Claudio Pacchierotti, Eric Marchand, and Maud Marchal.
\enquote{How Different Is the Perception of Vibrotactile Texture Roughness in Augmented versus Virtual Reality?}.
In: \textit{ACM Symposium on Virtual Reality Software and Technology}. Trier, Germany, October 2024. pp. 287--296.
