YOU are playing a video game, and your avatar is creeping into a haunted house at the dead of night. Suddenly, you freeze in your chair. Something is crawling up your back...
Whether this idea appeals or not, researchers at Disney have made such sensations possible by inventing a system that fools players into thinking that objects are moving against their skin.
Their brainchild, known as Tactile Brush, creates the illusion of being touched by anything from falling rain to crawling insects.
One of the illusions the team employs is called apparent tactile motion. If two vibrating objects are placed close together on skin in quick succession, people often experience this as a single vibration moving between the two points of contact. In a related illusion, known as a phantom tactile sensation, a pair of stationary vibrations is sensed as a single stimulus placed in between the two.
Apparent motion has been around since the early 1900s and phantom sensation since 1957, but this is the first time anyone has used them to provide precise tactile feedback.
Ali Israr and Ivan Poupyrev at Disney Research Pittsburgh studied these illusions with the help of volunteers who sat in a chair backed by a grid of 12 vibrating coils. By operating the coils in different sequences and at different intensities, they worked out how to induce the sensations of apparent motion and also persuade the volunteers that they were feeling extra coils that didn't exist, which creates a more realistic effect. Israr and Poupyrev incorporated these two illusions into software that controlled the coils, which convinced the person sitting in the chair that shapes were moving across their back.
At the Conference on Human Factors in Computing Systems, held last week in Vancouver, Canada, the researchers demonstrated a driving game that makes use of Tactile Brush. Players feel a force from the chair that mimics the experiences of cornering and accelerating by activating the coils in sequence to sweep across the back.
In other early tests, Israr and Poupyrev have simulated the sensation of raindrops running down skin by tracing a vertical line downwards. Israr describes skin as an unexplored display surface. "Two metres squared - that's the total area of our skin," he says. "It's a big area."
The team is also working on a wearable device with vibrators in the sleeves and around the torso. Disney wants to develop systems that could augment the company's amusement park rides. Israr suggests that riders could experience the sensation of wind and rain sweeping over them, or insects crawling over their backs.
"I'd really like to get it into movie theatres," adds Poupyrev. He says it would help movies to compete with DVDs and home cinema. "3D is already there. Movie theatres will become more like amusement parks. Movies will engage all the senses."
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