A variety of devices currently on the market provide simple forms of touch feedback, but none is an unqualified success - they all lack some aspect of physical experience, a correspondence with the way we actually interact with the world. Current tactile solutions fall short either in reconfigurability or in pre-interaction feedback. This pre-interaction feedback would provide the physical feeling of a button which the user can press or not, rather than just a tactile confirmation that they have just pressed that button. Reconfigurability would allow physically felt controls to change with the content of the display. In short, it’s easy to make static physical buttons, but not to make them disappear when not needed. And it’s easy to provide a physical sensation after the user interacts, but not to provide buttons that can be physically felt *before* the interaction is committed.

Several tactile feedback solutions have been proposed, explored in concepts, and in some cases brought to market to try make tactile feedback more realistic:

Physical overlays
This is a vinyl sheet placed atop the display, with holes to physically simulate buttons. The overlay solution is the least flexible, since it doesn’t reconfigure when the display changes (say when you’re watching a movie instead of typing). But this solution is possible, present in the market, and in at least one test case (Nintendo Emulator overlay), does apparently add some utility.

Air or Liquid filled bladders
One device concept that seems to regularly make the rounds (reported early on by Gizmodo) suggests using liquid beneath the display surface to create real, touchable buttons on the surface of the device. While this solution may have some promise, no viable forms have yet appeared in the market, and several commenters have suggested the idea may not be implementable as described.

Piezoelectric mechanisms
A Nokia patent using piezoelectrics for a similar end was reported a few months back, and Apple has also patented some similar technologies. Market-ready versions of this technology have yet to be seen, but would likely have real promise as an apparently viable solution letting users feel buttons before they interact.

Pressable mechanical touchscreen
The Blackberry Storm touch-sensitive smartphone, whatever its other faults, did add a great tactile interaction. The entire screen presses in slightly (and evenly) when a button is pressed, giving the sensation of an actual button press. There is still no button-like tactile feedback prior to the press, but the press itself is surprisingly satisfying. And this approach lets the phone distinguish between ‘highlight’ and ‘press’ interactions, akin to the difference between ‘rollover’ and ‘click’ interactions when using the web on a PC. This clever and well-integrated tactile solution thus provides an additional level of control beyond that of competing devices.

The Band-aid display
A wearable flexible miniaturized tactile display also apparently uses piezoelectrics to deliver touch sensations directly to the fingertips. This solution could enable more flexible braille displays for the blind as well as enabling a ‘Minority Report’ style mid-air interaction (not that we’re convinced that’s actually the best ultimate solution for device interactions), but is still a ways off from commercial production.

Nanotech
More distant-future design concepts like Nokia’s ‘Morph’ nanotech phone concept also propose a physically reconfigurable tactile surface. Nanotech concepts will obviously take some time to come to market, when and if they do, but offer much more versatile solution, suggesting that devices can physically reconfigure to a much greated extent than in the solutions above.

Ultrasound
Even further out there (both in development time and in plausibility): ultrasound to simulate touch. This solution is complicated - the device has to track hand position in order to simulate feedback, and ultrasound has the potential to blow out eardrums if over-amplified. If current mobile devices interfere with pacemakers just imagine what mobile ultrasound devices could do. Here’s a Video of ultrasound interaction.

Summing Up
The implications for all these solutions are interesting but there are obvious potential drawbacks. Potential issues include the physical durability of the display, the protection of the display itself (How delicate would a piezoelectric screen be?), the safety of users (How can we ensure that ultrasound harms neither ears nor pacemakers?), and even the readability of visuals (Does reconfiguring the surface actually distort the image displayed?).

Personally, I would love to see mobile touch devices with real tactile sensations for buttons (and even more  for other interactions - sliders, checkboxes, etc.). I have yet to see a tactile feedback device that approaches this goal. I believe the team that ultimately solves the problem and creates a physically ‘real’ experience that is still reconfigurable will gain a profound competitive advantage in the mobile market and beyond. That this has not already been achieved speaks to the difficulty of the problem.

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