June 14, 2013
Vibrations Felt On Skin May Aid In Tactile Display Innovation
Brett Smith for redOrbit.com - Your Universe Online
Electronic distractions that can be dangerous while driving, such as a GPS system or text message, have created a need to convey information in a non-visual way.
MIT researcher Lynette Jones believes she has come up with a solution to that problem: tactile ℠displays´ that send information through vibrating pulses.
"If you compare the skin to the retina, you have about the same number of sensory receptors, you just have them over almost two square meters of space, unlike the eye where it's all concentrated in an extremely small area," Jones explained. "The skin is generally as useful as a very acute area. It's just that you need to disperse the information that you're presenting."
Conveying information through sense of touch presents a major problem: differences in sensitivity. Areas of the hand might be more sensitive than the forearm, or vice versa.
To answer this question of sensitivity, Jones built an array that determines a motor's vibrations through skin in three dimensions, according to her report in the journal IEEE Transactions on Haptics. Using eight tiny accelerometers and a single vibrating motor typically used in cellphones, Jones configured the array to measure motor vibrations in three different body regions: the palm, the forearm and the thigh.
Through performing experiments with eight healthy volunteers, Jones found that vibrations through skin drop off quickly in all three areas, within 8 millimeters (0.3 inches) from the vibrating source.
However, participants' perceptions of these vibrations showed something different. A separate experiment by Jones showed that although the skin stopped vibrating 0.3 inches from the source, most participants continued to recognize the vibrations as far away as an inch from the source.
Jones also asked participants to pick out a specific motor within a 3-by-3 array of phone motors. While participants were the most sensitive on their palm, they were better at picking out vibrations in the four outer corners of the array in all three test regions. Jones concluded people use the edges of their limbs to localize stimuli.
"For a lot of sensory modalities, you have to work out what it is people can process, as one of the dictates for how you design," Jones said. "There's no point in making things much more compact, which may be a desirable feature from an engineering point of view, but from a human-use point of view, doesn't make a difference."
In addition to creating an ℠eyes-free´ display for drivers, Jones said tactile information could be used by firefighters in a smoke-filled building or by emergency workers in a disaster site. Besides being used by first responders, Jones said tactile displays could help joggers or bikers traverse an unfamiliar route by receiving signals from a buzzing wristband.
Jones and her colleagues said they are currently designing arrays that can be worn on the back and around the wrist. These vibrating arrays could be activated from left to right to tell a driver to turn right or left.
"There's a lot of things you can do with these displays that are fairly intuitive in terms of how people respond," Jones said, "which is important because no one's going to spend hours and hours in any application, learning what a signal means."