Testing the Effectiveness of a Vibrotactile Device
for Crossing Streets by Deaf-Blind People
By Dona Sauerburger, COMS
NOTE from author: I wrote this unpublished report in 1987 or 1988 after learning that somewhere in the Mid-Atlantic area was a deaf-blind man who crossed streets using a vibrotactile device, the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 manufactured the Tactaid, Audiological Engineering Corporation, graciously sent their current model, the Tactaid II, to be tested.
The Tactaid II is no longer available -- it was further developed but by now, even the newer model has been discontinued.
The language of this report reveals my undeveloped understanding of analyzing uncontrolled crossings, for example using the word "safe" inappropriately, and reporting that a car was heard "far enough away" rather than "with enough warning."
Nevertheless, it remains an interesting example of using the TMAD to evaluate the effectiveness of tools or strategies to aid in the detection of approaching vehicles, although the more important factor is teaching our students to be able to evaluate situations and the effectiveness of their detection of vehicles themselves -- for more information, see the Self-Study Guide for uncontrolled crossings.
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 the Audiological Engineering Corporation. This device transforms most sounds into frequencies with vibrations that can be detected tactually with two receptors, placed either on the wrist or chest. The Timing Method for Assessing the Detection of Vehicles was used to test its effectiveness in detecting vehicles, and the figures below show how many seconds it took from the time the evaluator, using the device, detected the vehicle until the vehicle reached her.
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; in seconds): 6:45
From the right (coming downhill; in seconds): 2:7; 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 level, two-lane 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 (in seconds): 2:4; 3:7; 3:9; 4:0; 4:3; 5:2; 5:9; 6:6; 6:7
From the left (in seconds): 3:7; 3:9; 4:0; 4:0; 5:1; 6:3; 6:5; 7:2; 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.
Time from the detection of the vehicle until the vehicle's arrival at the crosswalk:
From the left (in seconds): 4:6; 5:1; 5:5; 6:4; 7:2; 8:6; 8:8
From the right (in seconds): 3:9; 4:3; 4:7; 5:9; 6:0; 6:5; 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.
UPDATE, 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 (in seconds):
3:0; 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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