Touch Screen With a Tactile Feel – A Magical User Experience

[dropcap]T[/dropcap]ouch screens are a great interface.  They lack, however, the elements of haptic/ tactile feedback.  We all enjoy watching videos and still images on it, so much so that at times we even want to touch it so as to have a real feel of the visual contents in front of us, but all we get back is a cold and bland smoothness.

This is going to change, thanks to Pittsburgh branch of Disney Research; a network of research laboratories supporting Walt Disney Company through scientific and technological innovation to further the company’s media and entertainment efforts.

Led by research engineer Ali Israr, the research team has developed an algorithm that creates 3D haptic effects by controlling the friction forces on finger tips sliding over the touch screen display.  One can now feel the bumps and curves of the hills and valleys of the displayed scene.  

The whole process of 3D tactile/ haptic effect is centered upon perception- a brain game.  When we slide our finger over a real physical bump, we get the “feel” of the bump because of the friction forces stretching and compressing the skin on our sliding finger.  This skin stretch/ compression sends signals to our brain. The brain precesses these signals and gives us back a sense of a 3D bump.  Aided by a visual signal this perception is further enhanced.

The Disney Research team has employed electro-vibration by using a capable display to vary the friction between the sliding finger and the touch screen with electrostatic forces.  This way they have successfully developed and validated a psychophysical model closely simulating the feel of a real bump.

Using this psychophysical model they further developed an algorithm that modulates in real time the frictional forces on a sliding finger.  The modulated frictional forces closely match the tactile properties of the visual content on the touch surface.  As a result the brain is fooled to perceive the image of a bump to have the feel of a real bump.

This algorithm has three main steps:

1. Computing the gradient of the visual content to be rendered.  For real objects depth maps are used.

2.  Determining the dot product of the gradient of the virtual surface and velocity of the sliding finger.

3.  Mapping the dot product to the voltage using the psychophysical model.

By using this clever algorithm in combination with an electro-vibration capable touch screen display, 2D images are believed  by the brain to be 3D objects which they are not.  A trick of perception! A cactus will feel thorny and a ball will feel round.

There are other complexities and mathematical details of this interesting research but the end result is simple; a believable tactile sensation matching the visual content for a great immersive user experience! 


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