This was written in 1987 or 1988 after learning that
somewhere in the Mid-Atlantic area was a deaf-blind man who crossed streets
using a vibrotactile device, the Tactaid,
to detect the sounds of approaching vehicles.
The company that invented and manufactures the Tactaid,
Audiological Engineering Corporation, graciously sent their current model, the Tactaid II, to be tested.
The Tactaid II is no longer available, as the Tactaid has been further developed and probably warrants
another investigation to see if it is (or can be adapted to become) an
effective option for deaf-blind people to detect approaching vehicles.
Testing the Effectiveness of a Vibrotactile Device for Crossing Streets by Deaf-Blind
People
By
Dona Sauerburger, COMS
The following data has been gathered using
a vibrotactile device to see if it can enable a
deaf-blind pedestrian to detect vehicles sufficiently to enable him to cross a
street safely. The vibrotactile
device is TACTAID II, manufactured by Audiological
Engineering Corporation in
The evaluator was a sighted hearing
person, not only using the vibration from the device but also the sound it
emits with even its most faint vibration.
A deaf-blind person, therefore, may not be able to detect the vibrations
as quickly, so that the results of this experiment will not only be different
for each intersection, as these trials show, but for each deaf-blind person, as
people’s ability to detect the vibrations may vary.
FIRST TRIAL:
Street: Inside a small
residential development, about a block from the entrance; halfway up a steep
hill. The speed limit is 30, and cars go
about 35 mph. It takes 5.7 seconds for
the evaluator to walk quickly across the street.
Time from the detection of the vehicle
until the vehicle’s arrival at the crosswalk:
From the left (coming uphill): 6:45 seconds
From the right (coming
downhill): 2:7 sec.
3:9
4:5
Conclusion: the car from the
left was detected far enough away, but none of the cars from the right were
detected in time to allow a crossing. If
the person had started to cross just before detecting any cars, the cars would
all have had to slow down to avoid hitting her, and one of the cars would have
been only 3 seconds away from impact, probably too close to have been able to
avoid a collision. Cars coasting down
steep hills are too quiet and fast to be detected safely using the vibrotactile device.
SECOND TRIAL:
Street: A two-lane
level highway, with a curve about a block to the right (the curve blocks
visibility but the cars are still audible).
Speed limit is 55, the cars go about 55 mph from the left, and almost
that fast from the right after making the curve. It took the e evaluator 5:8 seconds to walk
quickly across the street.
Time from the detection of the vehicle
until the vehicle’s arrival at the crosswalk:
From the right: 2:4 sec. From the left: 3:7 seconds
3:7 3:9
3:9 4:0
4:0 4:0
4:3 5:1
5:2 6:3
5:9 6:5
6:6 7:2
6:7 7:4
8:6
Conclusion: Eleven of the
19 vehicles reached the evaluator in much less time than required to complete a
crossing. Some of the vehicles were
going at such a speed that the drivers would probably have been unable to see
the pedestrian in time to stop for her.
Thus, the vibrotactile device did not provide
sufficient detection to cross this highway.
THIRD TRIAL:
Street: A residential street, slightly sloped uphill to the right, with the top of
the hill about a block and a half away, level on the left and curved slightly
but still visible and audible for about two blocks. Speed limit was 30, cars went about 30-40
mph. It took the evaluator 5:8 seconds
to walk quickly across the street.
From the left: 4:6 seconds From
the right: 3:9 seconds
5:1 4:3
5:5 4:7
6:4 5:9
7:2 6:0
8:6 6:5
8:8 7:2
Conclusion: The results
were better but still not perfectly safe.
Six of the 14 vehicles were able to reach the evaluator in less time
than was needed to cross. The vehicle
that arrived in the shortest time was 3:9 seconds. When that vehicle arrived, the pedestrian
would have been almost halfway across the second lane, and the vehicle would
have had to slow down to avoid hitting her.
The deaf-blind pedestrian, if he can detect the vibrations as well as
the evaluator did, can detect the majority of vehicles on this street safely, but
he must be aware that some vehicles will not be detected in time, and will hit
him if they don’t slow down. If he still
chooses to cross with this device, he should do everything possible to make himself visible, and to alert the driver of his intention of
crossing, since he is relying on the driver’s ability to see and avoid him.
NOTES:
The wind and other noises (such as other
pedestrians and chirping birds) also set off the Tactaid’s
vibration. The sounds from a
pedestrian’s footsteps and a bird’s chirping are regular and rhythmic, enabling
the user to detect other vibrations from vehicles between chirps and
footsteps. However, the wind must die
down for the vibrotactile device to be effective,
since the vibrations from the wind are at first indistinguishable from those of
approaching vehicles. Naturally, the
deaf-blind user will be aware that the wind is interfering, and can wait until
the wind dies down.
These trials were done with the device
facing perpendicular to the street, in a neutral position. It seemed to make little difference whether
the vibrotactile device was aiming toward the vehicle
or away – there was only a slight increase in sensitivity when it was facing
the vehicle. The advantage of it facing
the oncoming vehicle would probably be offset by the disadvantage that the
device might happen to be facing left when a vehicle approaches from the right,
and by the time it is turned to face the vehicle, the device would probably
have already detected the vehicle if it had been left in a neutral position.
June 24, 1988 – The device was tried by a totally blind man with
profound deafness. It took a maximum of
6:0 seconds for him to walk quickly across his street. The time it took vehicles to reach him after
he detected them with this device were:
3:0 seconds
3:6
4:1
4:3
5:0
6:0
6:1
He decided it was unsafe to
cross using the vibrotactile device, as the cars
would have reached him before he could complete the crossing, and he did not
want to rely on the drivers to stop for him.
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