Hello, I'm Dr Maxime Reynal from the Multimodal Interaction Group
at the University of Glasgow, and i'm going to present a work done with Dr Euan Freeman
and Prof Stephen Brewster about Pseudo-Haptic Effects for acoustic levitation displays.
Acoustic levitation displays allows to levitate small particles and to provide mid-air haptics
using ultrasounds. It is possible to manipulate simultaneously and independently these physical
elements of content. However, approaching the hands too close from the levitation area
to perceive haptics can generate instability and can cause the particles to drop.
Therefore, we are looking for new ways to create haptic feedback outside of the levitation area.
Pseudo-haptic effects are a good candidate to solve this issue.
They are based on visual illusions and proprioception. They do not require to
complicate the technology while providing haptics away from the levitation area.
When the user is moving a particle with gestures to point, select, and drag it, pseudo-haptic
effects allow to trigger haptic sensations by creating variations between particle movement path
and user's gestures. This can be achieved by modulating the Control/Display ratio.
This research has two goals: providing haptics outside the levitation display,
and enriching interaction with this emerging technology.
The two of them are addressed by considering the principle of pseudo-haptic effects.
I'm now going to present how we have implemented, and how we plan to evaluate
a set of effects such as Friction, Slippery, Texture, Stickiness, Inertia and Stiffness.
Effects of Friction and Slippery can both be seen as first steps towards providing the
perception of textures. Their principle is to modulate the velocity of the control particle
according to user's gestures. We aim at providing a Friction effect by reducing
the Control/Display ratio and, for Slippery effect, by increasing it.
The animation on the left shows a use case of Friction, which is enabled within the red areas.
It can then be used to guide the user during a dragging operation over a levitating particle.
Texture effect is achieved by coupling Friction and Slippery effects, while manipulating particle
movement path. We intend to finely synchronize particle spatial position, with Friction effect
for climbs, and Slippery for descents, as it has previously been done for mouse pointers.
We plan to test different paths for the particles,
as shown here, to provide different sort of textures to the users.
Stickiness effect is for providing resistance. It has already been
implemented for on-screen manipulation. The animation here shows that our implementation
decelerates the particles starting from a first predefined point in the levitation area,
until a second point, where the particle will be eventually attracted to a third point.
For providing the users with an understandable way to decelerate particles velocity,
we intend to evaluate three different functions that reduce Control/Display ratio according to
particle x-position between points d and a, as shown on these graphs.
The last two effects are not surface properties like the other ones.
Inertia is intended to provide a mass to an object. We aim at reproducing physical laws
to provide the users with a sense of weight, and eventually, with realistic, predictable behaviors.
Finally, pseudo-haptic effects can also be a way to enrich the interaction with levitating objects,
by giving them progressive rigidity. from compliance to deformation. Stiffness effect
differs from the previous ones as it can only be applied to compound objects,
and not to one particle only.
To sum up, one of the main limitation of acoustic levitation displays is
that interacting with the content inside the levitation area can interfere with ultrasound
field and cause the content to collapse.
Pseudo-haptic effects would allow to get around this limitation by providing the users with
haptic sensations outside the levitation area, while offering a wide range of sensations,
ranging from Friction to the simulation of physical laws leading to known,
understandable behaviors. Next step is to evaluate these effects with a series of user studies.