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Erwan Normand
2025-05-01 22:31:51 +02:00
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7
3-perception/xr-perception/5-discussion.tex
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The results showed a difference in vibrotactile roughness perception between the three visual rendering conditions.
Given the estimated \PSEs, the textures were on average perceived as \enquote{rougher} in the \level{Real} rendering than in the \level{Virtual} (\percent{-2.8}) and \level{Mixed} (\percent{-6.0}) renderings (\figref{results/trial_pses}).
A \PSE difference in the same range was found for perceived stiffness, with the \VR perceived as \enquote{stiffer} and the \AR as \enquote{softer} \cite{gaffary2017ar}.
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%However, the difference between the \level{Virtual} and \level{Mixed} conditions was not significant.
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Surprisingly, the \PSE of the \level{Real} rendering was shifted to the right (to be "rougher", \percent{7.9}) compared to the reference texture, whereas the \PSEs of the \level{Virtual} (\percent{5.1}) and \level{Mixed} (\percent{1.9}) renderings were perceived as \enquote{smoother} and closer to the reference texture (\figref{results/trial_predictions}).
The sensitivity of participants to roughness differences also varied, with the \level{Real} rendering having the best \JND (\percent{26}), followed by the \level{Virtual} (\percent{30}) and \level{Mixed} (\percent{33}) renderings (\figref{results/trial_jnds}).
These \JND values are in line with and at the upper end of the range of previous studies \cite{choi2013vibrotactile}, which may be due to the location of the actuator on the top of the finger middle phalanx, being less sensitive to vibration than the fingertip.
@@ -23,11 +20,9 @@ The \level{Mixed} rendering had the lowest \PSE and highest perceived latency, t
Our wearable visuo-haptic texture augmentation system, described in \chapref{vhar_system}, aimed to provide a coherent visuo-haptic renderings registered with the \RE.
Yet, it involves different sensory interaction loops between the user's movements and the visuo-haptic feedback (\figref[vhar_system]{diagram} and \figref[introduction]{interaction-loop}), which may not feel to be in synchronized with each other or with proprioception.
%When a user runs their finger over a vibrotactile virtual texture, the haptic sensations and eventual display of the virtual hand lag behind the visual displacement and proprioceptive sensations of the real hand.
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Thereby, we hypothesize that the differences in the perception of vibrotactile roughness are less due to the visual rendering of the hand or the environment and their associated differences in exploration behaviour, but rather to the difference in the \emph{perceived} latency between one's own hand (visual and proprioception) and the virtual hand (visual and haptic).
The perceived delay was the most important in \AR, where the virtual hand visually lags significantly behind the real one, but less so in \VR, where only the proprioceptive sense can help detect the lag.
This delay was not perceived when touching the virtual haptic textures without visual augmentation, because only the finger velocity was used to render them, and, despite the varied finger movements and velocities while exploring the textures, the participants did not perceive any latency in the vibrotactile rendering (\secref{results_questions}).
\textcite{diluca2011effects} demonstrated similarly, in a \VST-\AR setup, how visual latency relative to proprioception increased the perception of stiffness of a virtual piston, while haptic latency decreased it (\secref[related_work]{ar_vr_haptic}).
Another complementary explanation could be a pseudo-haptic effect (\secref[related_work]{visual_haptic_influence}) of the displacement of the virtual hand, as already observed with this vibrotactile texture rendering, but seen on a screen \cite{ujitoko2019modulating}.
Such hypotheses could be tested by manipulating the latency and pose estimation accuracy of the virtual hand or the vibrotactile feedback. % to observe their effects on the roughness perception of the virtual textures.
Such hypotheses could be tested by manipulating the latency and pose estimation accuracy of the virtual hand or the vibrotactile feedback.