\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.
%we rendered virtual vibrotactile patterned textures on the voice-coil worn on the middle-phalanx of the finger to augment the roughness perception of the real surface being touched.
With an immersive \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} and with a higher sensitivity when touched with the real hand alone than with a virtual hand either in \AR, with \VR in between.
Exploration behaviour was also slower in \VR than with real hand alone, although subjective evaluation of the texture was not affected.
We hypothesised 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.

%We can outline recommendations for future \AR/\VR studies or applications using wearable haptics.
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 synchronised 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 reality-virtuality can affect the asynchrony sensation of the latencies, even though they remain identical.
When designing for wearable haptics or integrating it into \AR/\VR, it seems important to test its perception in real, augmented and virtual environments.
%With a better understanding of how visual factors influence the perception of haptically augmented real objects, the many wearable haptic systems that already exist but have not yet been fully explored with \AR can be better applied and new visuo-haptic renderings adapted to \AR can be designed.
%Finally, a visual hand representation in OST-\AR together with wearable haptics should be avoided until acceptable tracking latencies \are achieved, as was also observed for virtual object interaction with the bare hand \cite{normand2024visuohaptic}.

\noindentskip This work was presented and published at the VRST 2024 conference:

Erwan Normand, Claudio Pacchierotti, Eric Marchand, and Maud Marchal.
(2024).
\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}, pp. 287--296.
\textsc{doi}: \href{https://doi.org/10/g5rr49}{10/g5rr49}.
