Hello everyone, my name is Sebastian Günther from the Technical University of Darmstadt
and today I‘m going to present you on the behalf my co-authors the results of our work titled:
"Smooth as Steel Wool –
Effects of Visual Stimuli on the Haptic Perception of Roughness in Virtual Reality".
Without much doubt, we all know: Virtual Reality is fun!
It allows us to explore amazing new worlds and to enjoy immersive experiences.
However, these experiences are still mostly visual and limited in haptics which is essential
for more lifelike sensations.
Although we are already able to simulate physical touch through vibrotactile or pressure-based
feedback, material characteristics of objects or the environment, such as temperature, stiffness,
stickiness, and roughness are less explored.
In this work, we investigated the aspect of roughness and took a deeper look into moving
stroke sensations along the arm with different levels roughness.
Further, we studied how haptic and visual stimuli affect the perception of roughness
in Virtual Reality for matching and realistic experiences.
For this, we first conducted a pre-study with 40 participants in order to identify
the expected roughness of 50 different items and potential visualizations.
Then, we took ten of these items clustered according to their expected roughness and
conducted a second user-study with 31 participants to investigate the interdependency of haptic
stroking stimuli and visualizations.
In addition, we compared the effects on perceived roughness, matching,
realism, and pleasantness with state-of-the-art vibrotactile phantom sensations and real-world
materials of the visualizations.
That being said, through our pre-study, we were able to gather 10 visualizations categorized
into five even levels of roughness.
A very smooth spoon and silk fabric.
A smooth cotton pad and fingertip.
A neither smooth or rough bottom-side of a sponge and toothbrush.
A rough wooden stick and edgy rock.
And a very rough piece of steel wool and sandpaper file.
All of them were then modelled in 3D, as you can see here, for the follow up study where
we explored how they interact with haptic stroke stimuli.
For the haptic stroke stimuli, therefore, we used different physical textures:
a very smooth high-gloss strip of polyethylene and four gradations of sandpaper with different
roughness.
Then, we mounted them on silicone actuators that could be moved along the arm on a guiding
rail.
The actuators thereby were inflatable in order to provide an even contact with the skin.
In addition to these five textures, we also designed actuators that were using the real-world
materials of each visualization as one of our baselines.
Overall, this resulted in nine haptic stimuli consisting of the five textures,
the real physical materials,
a state-of-the-art vibrotactile actuation using phantom sensations,
the silicone actuator without any texture, and a no-haptics baseline that did not apply
any haptic stimulus.
All of them were then combined with the ten previously selected visualizations and a no-visual
baseline for a total of 99 conditions.
So, how did this look like during the study?
As you can see here, we used a stationary setup that could move all physical actuators
along the arm to provide the haptic stroking stimuli depending on the condition.
The participant, however, was situated in a virtual environment seeing a similar room
and, most importantly, the current visualization of a condition moving synchronously to the
haptic stimulus along the arm of their virtual avatar.
After each condition, we then asked the participants to rank the following items on 5-Point scales
in questionnaires.
The perceived roughness of the haptic stimulus.
The roughness of the shown visualization.
The matching of the haptic stimulus and visualization.
The consistency of the actuation with real world experiences.
And the pleasantness of the actuation.
In total, we had 31 individuals participating during this study.
And we analyzed their responses with various statistical methods, which are described in
more detail in the paper.
The analyses revealed several interesting things, of which I would like to highlight
the most important.
Most interestingly, we found that two distinct textures were sufficient for a matching and
realistic experience.
Both, matching and realism ratings, were always high as long as the haptic stimulus was close
to the expected roughness of a visualization.
In particular, a very rough haptic stimulus could match all visualizations that were either
rough or very rough.
While on the other side, a smooth stimulus matched all visualizations that were very
smooth or smooth in their appearance.
As a consequence, future haptic devices could save physical space by providing less physical
textures and are still able to create the illusion of a matching and realistic experience.
Second, some visualizations had different expected roughness as the haptic stimulus
but were still rated high in their matching.
For example, the spoon only worked well with a smooth texture, but not with a rough one.
The steel wool, on the other side, only worked well with a rough texture, but not with a
smooth one.
However, it was different for the rock.
Although the visualization was visually perceived as rough when it was combined with a smooth
stimulus, the participants still gave a high matching rating.
Hereby we could observe, that this resulted by a change in the general notion of the rock
as participants could also interpret the rock as a rather smooth pebble instead of the edgy
rock they typically had in mind.
As a result, the haptic stimulus is able to override the anticipated roughness expectation
of visualizations on the other side of the roughness scale, as long as the object would
also occur naturally as smooth or rough even if the initial notion would be contrary.
Further, we could identify that the Pleasantness rating depends not only on the roughness but
also on the matching of a haptic stimulus and visualization.
In general, smooth stimuli are perceived more pleasant compared to rough stimuli which is
also in align with existing work.
However, we could also observe that also smoother visualizations felt significantly more unpleasant
when combined with rough or very rough stimuli than rougher visualizations with the same
rough haptic stimuli.
For example, when using a rough texture with a spoon, it was rated as unpleasant.
But combining the rough texture with a more matching toothbrush, the pleasantness of the
actuation was rated higher.
This is a particularly interesting result, as it can be used for future applications
to ensure pleasant experiences when using matching stimuli, however, also to intentionally
create unpleasant settings by opposing haptic and visual roughness.
To summarize, we investigated the effects of visual stimuli on the haptic perception
of roughness in virtual reality through two user studies,
and found that two levels of roughness are sufficient for a realistic and matching experience,
that visualizations can adapt to haptic stimuli, and that the pleasantness depends on roughness
and matching, along with other findings, which can be found
in the paper.
With that, I would like to thank you for your attention and if you have any questions or
comments, feel free to contact me.
Thank you!