[Nfbf-l] MIT Scientist Designs Wearable Tactile Displays for People With Vision and Hearing Disabilities

[Alan Dicey]

MIT Scientist Designs Wearable Tactile Displays for People With Vision and 
Hearing Disabilities
Jun 17, 2013
In the near future, a buzz in your belt or a pulse from your jacket may give 
you instructions on how to navigate your surroundings.

Vibrotactile displays mounted around the waist and back are used to study 
how people use vibrotactile cues to navigate in unfamiliar environments. 
(Photo courtesy of the researchers)

Think of it as tactile Morse code: vibrations from a wearable, GPS-linked 
device that tell you to turn right or left, or stop, depending on the 
pattern of pulses you feel. Such a device could free drivers from having to 
look at maps, and could also serve as a tactile guide for people with vision 
and hearing disabilities.

Lynette Jones, a senior research scientist in Massachusetts Institute of 
Technology's Department of Mechanical Engineering,
designs wearable tactile displays.
Through her work, she's observed that the skin is a sensitive - though 
largely untapped -
medium for communication.

"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 says. "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."

Knowing just how to disperse tactile information across the skin is tricky. 
For instance, people may be much more sensitive
to stimuli on areas like the hand, as opposed to the forearm, and may 
respond best to certain patterns of vibrations. Such information on skin 
responsiveness could help designers determine the best configuration of 
motors in a display, given where on the skin a device would be worn.

Now Jones has built an array that precisely tracks a motor's vibrations 
through skin in three dimensions. The array consists of eight miniature 
accelerometers and a single pancake motor - a type of vibrating motor used 
in cell phones. She used the array to measure motor vibrations in three 
locations: the palm of the hand, the forearm and the thigh. From her studies 
with
eight healthy participants, Jones found that a motor's mechanical vibrations 
through skin drop off quickly in all three locations, within 8 millimeters 
from where the vibrations originated.

Jones also gauged participants' perception of vibrations, fitting them with 
a 3-by-3 array of pancake motors in these three locations on the body. While 
skin generally stopped vibrating 8 millimeters from the source, most people 
continued to perceive the vibrations as far away as 24 millimeters.

When participants were asked to identify specific locations of motors within 
the array, they were much more sensitive on the palm than on the forearm or 
thigh. But in all three locations, people were better at picking out 
vibrations in the four corners of the array, versus the inner motors, 
leading Jones to posit that perhaps people use the edges of their limbs to 
localize vibrations and other 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," says Jones, whose 
results will appear in the journal IEEE
Transactions on Haptics. "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 measuring skin's sensitivity to vibrations, Jones and 
co-author Katherine Sofia '12 found that skin has a strong effect on motor 
vibrations. The researchers compared a pancake motor's frequency of 
vibrations when mounted on a rigid structure or on more compliant skin. They 
found that in general, skin reduced a motor's vibrations by 28 percent, with 
the forearm and thigh having a slightly stronger dampening effect than the 
palm of the hand.

The skin's damping of motor vibrations is significant, Jones says, if 
engineers plan to build tactile displays that incorporate different 
frequencies of vibrations. For instance, the difference between two motors - 
one slightly faster than the other - may be indistinguishable in certain 
parts of the skin.
Likewise, two motors spaced a certain distance apart may be differentiable 
in one area but not another.

"Should I have eight motors, or is four enough that 90 percent of the time, 
I'll know that when this one's on, it's this one and not that one?" Jones 
says. "We're answering those sorts of questions in the context of what 
information you want to present using a device."

Roberta Klatzky, a professor of psychology at Carnegie Mellon 
University,says that measurements taken by Jones' arrays can be used to set 
up displays in which the location of a stimulus - for example, a pattern to 
convey a letter - is important.

"A major challenge is to enable people to tell the difference between 
patterns applied to the skin as, for example, people who are blind do when 
reading Braille," says Klatzky, who specializes in the study of spatial 
cognition. "Lynette's work sets up a methodology and potential guidelines 
for effective pattern displays."

Jones sees promising applications for wearable tactile displays. In addition 
to helping drivers navigate, she says tactile stimuli may direct 
firefighters through burning buildings, or emergency workers through 
disaster sites. In more mundane scenarios, she says tactile displays may 
help joggers traverse an unfamiliar city, taking directions from a buzzing 
wristband, instead of having to look at a smartphone.

Using data from their mechanical and perceptual experiments, Jones' group is 
designing arrays that can be worn across the back and around the wrist, and 
is investigating various ways to present vibrations. For example, a row of 
vibrations activated sequentially from left to right may tell a driver to 
turn right; a single motor that buzzes with increasing frequency may be a 
warning to slow down.

"There's a lot of things you can do with these displays that are fairly 
intuitive in terms of how people respond," Jones says, "which is important 
because no one's going to spend hours and hours in any application, learning 
what a signal means."

Reproduced from
 http://globalaccessibilitynews.com/2013/06/17/mit-scientist-designs-wearable-tactile-displays-for-people-with-vision-and-hearing-disabilities/