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Erwan Normand
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3-perception/vhar-textures/1-introduction.tex
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\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}.
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 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.
In this chapter, we investigate whether simultaneous and \textbf{co-localized visual and wearable haptic texture augmentation of real surfaces} in \AR can be perceived in a coherent and realistic manner, and to what extent each sensory modality would contribute to the overall perception of the augmented texture.
We used nine pairs of \textbf{data-driven visuo-haptic textures} from the \HaTT database \cite{culbertson2014one}, which we rendered using the wearable visuo-haptic augmentatio nsystem presented in \chapref{vhar_system}. %, an \OST-\AR headset, and a wearable voice-coil device worn on the finger.
We used nine pairs of \textbf{data-driven visuo-haptic textures} from the \HaTT database \cite{culbertson2014one}, which we rendered using the wearable visuo-haptic augmentation system presented in \chapref{vhar_system}. %, an \OST-\AR headset, and a wearable voice-coil device worn on the finger.
In a \textbf{user study}, 20 participants freely explored in direct touch the combination of the visuo-haptic texture pairs to rate their coherence, realism and perceived roughness.
We aimed to assess \textbf{which haptic textures were matched with which visual textures}, how the roughness of the visual and haptic textures was perceived, and whether \textbf{the perceived roughness} could explain the matches made between them.

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3-perception/vhar-textures/3-results.tex
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@@ -58,7 +58,7 @@ Even though the consensus was high (\kendall{0.61}, \ci{0.58}{0.64}), the roughn
\paragraph{Visuo-Haptic Textures Ranking}
Also, almost all the texture pairs in the visuo-haptic textures ranking results were statistically significantly different (\chisqr{8}{20}{140}, \pinf{0.001}; \pinf{0.05} for each comparison), except for the following groups: \{\level{Sandpaper~100}, \level{Cork}\}; \{\level{Cork}, \level{Brick~2}\}; and \{\level{Plastic Mesh~1}, \level{Velcro Hooks}, \level{Sandpaper~320}\}.
The consezsus between the participants was also high \kendall{0.77}, \ci{0.74}{0.79}.
The consensus between the participants was also high \kendall{0.77}, \ci{0.74}{0.79}.
Finally, calculating the similarity of the three rankings of each participant, the \textit{Visuo-Haptic Textures Ranking} was on average highly similar to the \textit{Haptic Textures Ranking} (\kendall{0.79}, \ci{0.72}{0.86}) and moderately to the \textit{Visual Textures Ranking} (\kendall{0.48}, \ci{0.39}{0.56}).
A Wilcoxon signed-rank test indicated that this difference was statistically significant (\wilcoxon{190}, \p{0.002}).
These results indicate that the two haptic and visual modalities were integrated together, the resulting roughness ranking being between the two rankings of the modalities alone, but with haptics predominating.
@@ -85,7 +85,6 @@ Stiffness is indeed an important perceptual dimension of a material (\secref[rel
\fig[0.6]{results/matching_correspondence_analysis}{
Correspondence analysis of the confusion matrix of the \level{Matching} task.
}[
%The haptic textures are represented as green squares, the haptic textures as red circles. %
The closer the haptic and visual textures are, the more similar they were judged. %
The first dimension (horizontal axis) explains \percent{60} of the variance, the second dimension (vertical axis) explains \percent{30} of the variance.
The confusion matrix is \figref{results/matching_confusion_matrix}.
@@ -139,7 +138,7 @@ This shows that the participants consistently identified the roughness of each v
A non-parametric \ANOVA on an \ART model was used on the \response{Difficulty} and \response{Realism} question results, while the other question results were analyzed using Wilcoxon signed-rank tests.
On \response{Difficulty}, there were statistically significant effects of \factor{Task} (\anova{1}{57}{13}, \pinf{0.001}) and of \response{Modality} (\anova{1}{57}{8}, \p{0.007}), but no interaction effect \factor{Task} \x \factor{Modality} (\anova{1}{57}{2}, \ns).
The \level{Ranking} task was found easier (\mean{2.9}, \sd{1.2}) than the \level{Matching} task (\mean{3.9}, \sd{1.5}), and the Haptic textures were found easier to discrimate (\mean{3.0}, \sd{1.3}) than the Visual ones (\mean{3.8}, \sd{1.5}).
The \level{Ranking} task was found easier (\mean{2.9}, \sd{1.2}) than the \level{Matching} task (\mean{3.9}, \sd{1.5}), and the Haptic textures were found easier to discriminate (\mean{3.0}, \sd{1.3}) than the Visual ones (\mean{3.8}, \sd{1.5}).
Both haptic and visual textures were judged moderately realistic for both tasks (\mean{4.2}, \sd{1.3}), with no statistically significant effect of \factor{Task}, \factor{Modality} or their interaction on \response{Realism}.
No statistically significant effects of \factor{Task} on \response{Textures Match} and \response{Uncomfort} were found either.
The coherence of the texture pairs was considered moderate (\mean{4.6}, \sd{1.2}) and the haptic device was not felt uncomfortable (\mean{2.4}, \sd{1.4}).