Scanning for Cars
by Dona Sauerburger, COMS
People with less than 5 degrees of central
vision* usually need to scan
more slowly than they did when they had more vision because otherwise they’ll
miss seeing large objects. I realized
with alarm that this is also true when they look for cars -- if they glance too
quickly from right to left, they’ll usually miss seeing cars in what I call the
“blind spot,” which is about two car lengths to their left (where the driver
would be unable to stop if the student suddenly started to cross -- yikes!).
People with certain eye conditions such as
a central scotoma also have a problem with looking
quickly for cars, even after they’ve become skillful with eccentric viewing,
because they cannot see objects of low contrast at a distance unless the object
moves. Thus they cannot glance quickly
toward the left or right to see if there are any cars coming because they must
hold their gaze long enough to see the cars’ movement.
Most people can learn to scan
appropriately by using the following exercise:
1.
Find an appropriate street to practice:
For
narrow central vision,* the street should have only
one lane coming from the left, and lots of instances where only one or two cars
at a time come from the left (it can be a two-way street with traffic coming
from the right, but only one lane from the left – this is because it is
necessary to control the traffic that is presented and not have conflicting visual
information from other vehicles).
The student shouldn’t be able to hear cars
approaching closely -- a recorded masking sound and/or ear plugs can be used if
needed.
For
central scotoma, all that’s needed are lots of long gaps in
traffic from the right and the left (the number of lanes isn’t important).
2.
Have the student stand facing the street.
If the student is deaf and will rely on visual communication for this
exercise, have the student stand with the street on her left while the
instructor or interpreter faces the student with the street on his right.
3.
When the instructor gives the signal, the student turns to look for cars and
then looks back and reports whether there are any cars coming. The student should be instructed to look as
quickly as she can do so accurately, without missing any cars.
The instructor should give the signal to
look many times when there is nothing coming, and many times when there is a
car or cars that will be difficult to see without scanning properly:
For
narrow central vision,* the difficult situation is
when there is only one car and it’s in the “blind spot” (about 2 car lengths to
the left). The only practice needed is
for scanning to the left.
For
central scotoma, the difficult situation is when the only
cars visible are in the distance. These
students need to learn to scan to the right and to the left -- practice first
in one direction until the student is skillful, then the other direction; then
practice looking both ways.
4.
If the student misses seeing a car, she should realize she needs to improve and
try again:
For
the narrow central vision, scan more slowly;
For
the central scotoma, hold the glance a little
longer.
* This training is intended
only to prepare people to scan for crossing the street, but some people with
restricted visual fields also want to learn to scan the ground for obstacles. See “2) Override visual
information” in the article “Stages of Learning to Use a Cane” for
a discussion on the use of partial occlusion to encourage people to use their
cane for this information instead of their vision.
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