Hello everyone!
I am Shao-Yu Chu from National Taiwan University.
Today, I would like to present
MotionRing: Creating Illusory Tactile Motion around the Head
using 360° Vibrotactile Headbands.
Haptic feedback enhances virtual experiences.
Let’s take a look at some commercial haptic devices.
For example, there are game controllers
like Xbox, PS5, and Nintendo Switch.
There are also wearable devices,
like TactSuit from bHaptics.
We can see that vibration motors
are common in commercial haptic devices.
However, these devices provide only static vibrations.
This kind of feedback is of single point
and non-moving.
This limits them from creating suitable haptic feedback
for game events that include the sensation of movement.
For example, objects passing by the avatar,
or the rapid movement relative to the environment.
This is why we came to apparent tactile motion.
Apparent tactile motion is an illusion that allows users
to perceive a single but moving actuator
when vibrotactile stimuli are placed nearby
and are actuated with overlapped time series.
Here we present MotionRing,
a vibrotactile headband
that creates the sensation of motion around the human head
through apparent tactile motion.
The system works as follows.
When certain game events happen,
they are mapped to feedback patterns.
MotionRing then performs these feedback patterns.
The Arduino board controls the motor drivers,
which then actuates the array of vibration actuators in the headband.
Now we have our device system ready.
We would like to investigate
the control space of apparent tactile motion on the head.
Assume that there are two adjacent vibration motors.
One vibrates first, then the other.
From the temporal aspect,
we have the duration of the two vibrations.
Also, we have their onset interval.
Here we define the parameter as interstimulus onset interval
or ISOI in abbreviation.
To perform the apparent tactile motion,
we let an array of vibration motors vibrate in sequence.
When the ISOI is too short,
the user perceives one single vibration burst,
which lacks the sense of motion.
When the ISOI is too long, the user perceives discrete vibrations.
the user perceives discrete vibrations.
Only when the ISOI falls in a specific interval,
the user can perceive a single moving vibration.
Therefore, we would like to answer the following research question.
What are the upper and lower thresholds of ISOI
to present smooth tactile motion on the head?
We conducted a user study to understand
how the thresholds are affected
by the angular spacing of actuators,
head regions, vibration durations, and vibration intensities.
For the angular spacing of the actuators,
we implemented our prototype with three different versions,
with 45°, 30°, and 22.5° angular spacing, respectively.
In our pilot study, users reported that with the 45° design,
they only perceive discrete vibrations.
So we only leave the 30°- and the 22.5°-design
for the formal study.
For each prototype design,
we recruited 24 participants to join the user study.
Combinations of head regions, vibration durations,
and vibration intensities are fully counter-balanced.
For each combination,
we first experiment on the lower threshold of the ISOI,
then the upper one.
We follow the study procedure mentioned in Tactile Brush.
The initial ISOI value is set as 0 ms.
In every iteration,
we ask the participants if they can feel a single vibration burst.
If the answer is yes, we increase the ISOI value.
Otherwise, we decrease it.
The trial ends after the ISOI value reverses six times,
then we record the average of the last four reversals.
The upper threshold is quite the same,
except that the initial ISOI value is set as 300 ms,
and that we ask if the participant can feel discrete actuators.
We hypothesize that all four factors
affect both the lower and the upper ISOI thresholds,
including the angular spacing of actuators, the head regions,
the vibration durations, and the vibration intensities.
We then apply 4-way ANOVA to test our hypotheses.
The result shows that the angular spacing of the actuators,
the vibration durations, and the vibration intensities
significantly affect both the lower
and the upper ISOI thresholds.
But the head regions do not.
Moreover, the interaction
between the angular spacing of the actuators
and the vibration intensities
is also a significant factor.
These plots show the relationship
between the ISOI thresholds
and the three single-variable factors.
We can see that the ISOI thresholds increase
as vibration duration or the angular spacing increases.
As the vibration intensity increases,
the ISOI thresholds decrease.
After knowing the control space of apparent tactile motion
on the head,
we want to further evaluate the user experience of MotionRing.
We selected two games events that contain motion:
teleportation and objects flying by.
For teleportation,
we designed a VR treasure hunting game with scenes
in Half-Life Alyx.
We instructed the participants to teleport around
to search for items.
As they teleport, MotionRing vibrates according to
the direction and distance of their movement.
For example, if they teleport straight forward,
the two vibration motors locating at the middle of the forehead
vibrate first, following by the others,
performing a symmetric tactile motion.
For objects flying by,
we built a third-person view football dodging game with Unity.
We instructed the participants to control the avatar
to dodge the footballs by moving left and right.
As the football fly past the avatar,
vibration motors on the corresponding side vibrate in sequence,
from the front to the back.
In this case,
MotionRing performs an asymmetric tactile motion.
For both motion event types,
we compare three haptic feedback conditions:
MotionRing, static vibration, and visual-only.
The motors that vibrate for the first two conditions are the same.
The only difference is that for static vibration,
they vibrate simultaneously instead of in sequence.
As for visual-only, no haptics are applied.
The three conditions are counterbalanced by a Latin square.
We recruited 12 participants
to rate directionality, enjoyment, realism, and immersion
using 7-point Likert scales,
and rate the three haptic feedback conditions
based on their preference.
This plot shows the result of teleportation.
We can see that MotionRing has significantly higher scores
on directionality and enjoyment
when comparing to static vibration.
And it scores significantly higher
on all four aspects when comparing to visual-only.
Participants also comment that
MotionRing can well simulate the wind pressure in teleportation.
in teleportation.
This plot shows the result of the football dodging game.
MotionRing has a significantly higher score on directionality
when comparing to static vibration.
Participants comment that
MotionRing did create the sensation of a football flying by.
For preference,
92% and 75% of the participants
choose MotionRing as their top choice
for teleportation and football dodging, respectively.
We present MotionRing, a vibrotactile headband
that creates the sensation of 360° tactile motion
around the head.
We summarize a perceptual model for
creating apparent tactile motion around the head
that includes vibration duration, vibration intensity,
and motor spacing.
We propose symmetric and asymmetric tactile motion patterns
around the head for virtual experiences.
User evaluation showed significant improvement
in directionality and enjoyment
as well as being the most preferred by users.
This is the end of my talk. Thank you for listening!