Click here for videos of training for people with low acuity to scan / glance for street crossings
Training to Scan and Glance with Restricted Visual Fields
People with visual fields restricted to about 5 degrees of central vision usually need to learn to:
scan systematically, to avoid missing any areas;
scan slowly because even if they cover every area with their systematic scanning, they'll miss seeing objects if they do it too fast.
This page outlines some suggestions for training people to develop these skills.
It starts with simple scanning techniques on a wall or board, and ends with training for the extremely important skill of looking for vehicles when preparing to cross streets.
Who needs this training?
This training is usually necessary only for people whose visual fields are smaller than about 10-15 degrees.
People with larger visual fields are usually able to scan and glance effectively the same as they did before the visual field was so restricted.
Regardless of the size of the students' visual field, it is essential that their ability to scan and look for vehicles be assessed during their training for street crossings.
Considerations of restricted visual fields
Before starting the training, it is important to realize that the further that people with restricted visual fields are from an object, the more of it they can see.
This is illustrated with 4 pictures that I took at various distances from my cat and his orange brush.
I used a camera (shown to the right) with a tube attached in front of the lens to simulate a restricted visual field.
The first photo below was taken very close and all we can see is the cat's face -- if we had wanted to see the brush, we'd have to scan around and find it.
Each successive photo was taken from further away and we can see more and more of the cat and his surroundings.
The last picture was taken from across the room, and we can see the cat and the brush and the couch around them.
That means the closer they are to the area they are scanning, the more challenging it will be for them to find things.
They can see vehicles in the distance but may miss the ones nearby in what I call the "blind spot" (as illustrated in the fourth scene in the video to the right and explained below).
When looking for something on a desk, they may find it more easily by standing up and stepping away from the desk.
So to make the scanning tasks more challenging, position students close to the area where the scanning area and targets are --
if they are further away, they may be able to find the targets without even scanning.
To make the tasks easier for students with a very small visual field, position them further from the scanning area.
Initial Training to Scan
This training (as seen from the perspective of the student with the restricted visual field) is demonstrated in the video to the left.
The demonstration is on a brick wall, which is not recommended because the prominent lines make it too easy for the student to scan horizontally / vertically, as you can see in the video simulations.
However this may be desirable in the early stage of training for students who struggle with scanning -- once they become more skilled, you can either move to a smooth wall or cover up the brick with paper or material.
The training usually takes less than half an hour.
Wall or board which is at least 3 feet by 3 feet and which has no lines or visual clutter (if it is a board, mount it to the wall or whatever surface will be used for the training);
Tape which will not damage the wall or board;
Two strips of paper an inch or two wide and about two feet long;
Pen or marker thick enough to draw lines that can be easily seen by the student from a few feet away;
Small targets (can be objects or pieces of paper or material) about an inch square which can be affixed to the surface of the wall or board.
You may want targets with a range of contrasts with the background, from targets with high contrast to targets that differ from the background only in texture.
Place a target on the wall or board and find out how large an area the students can see at the distance they are from the target (as explained above, this area becomes larger when they move further from the wall or board).
Ask them to look at a target while you move one of your hands slowly toward the target and tell you when they see your hand.
When they report seeing your hand, make note of where the edge of their visual field is in that direction, and do it again from another direction until you have outlined their visual field around the target.
Measure the height of the visual field, and then write consecutive numbers along both strips of paper, with the numbers spaced apart the same distance as the height of the visual field.
Tape the strips to the wall, one on each side of the scanning area as shown in the photos below.
Students then scan horizontally from the first number on the top of one strip to the strip on the other side of the scanning area.
If they scan correctly, when they reach the other strip they will see the same number as the one they started out with on the first strip.
If they start at a number on the first strip and end up above or below that number on the second strip, they were not scanning horizontally -- have them try again.
Once they reach the second strip, they scan down till they are looking at the next number on the second strip, and then start scanning horizontally back to the first strip.
By looking down to the next number before starting to scan back, they will be scanning just below their previous scan, covering new areas without missing anything.
When they reach the first strip, they should see the same number as the one they started from on the other strip.
They continue in this manner, following a grid pattern like the one illustrated to the right.
When they can scan systematically well with the assistance of the numbered strips, remove one of the strips and have them scan again, as shown in the photo to the right.
They will start at the top number on the remaining strip and scan horizontally to the other side, then look down
exactly far enough to start their scan back to see the area just below their first scan.
If they do that correctly, they will reach the next number on the original strip.
They then look down again to the next number and repeat their scan across, down and back again, following the grid pattern that is illustrated to the far right.
Each time they return to the strip, they check to see if they arrived at the next number -- if not, they need to figure out if they were not scanning horizontally or if they scanned down too far or not far enough before scanning back to the strip.
Once they can scan systematically without missing any areas, they are ready to learn to scan slowly enough to see targets in that area.
Start with a target that is easy to see (high contrast such as the target in the first two photos below, and/or large with bright colors).
Later introduce targets that are harder to see, such as the one with low contrast in the pictures to the right below.
If you keep the strips up for this exercise, it can help the students make sure they are still scanning systematically while they focus on scanning slowly.
The final exercise is to find the targets without the strips, as shown in the photo below.
If they miss a target, you can ask them to try again while scanning more slowly, and/or put the strips back up and review the scanning technique to be sure they aren't missing any areas.
1. Before I start the training, I always ask students what kind of grid pattern they prefer to scan. Most prefer a horizontal pattern like the one explained, but some prefer to look up and down
(one preferred scanning in up-and-down columns while zig-zagging sideways in the column).
If they prefer to scan vertically, you can accommodate them by having the strips of paper horizontally at the top and bottom of the scanning area,
with the numbers on the strips spaced apart the same distance as the width of their visual field.
Then have them practice scanning from the beginning of the top strip down to the beginning of the bottom strip, then look sideways to the next number and scan back up to the first strip and so forth, following a vertical grid pattern across the wall or board.
2. When students miss the target, it can sometimes be difficult to determine if it was because they were scanning too quickly, or they weren't scanning systematically and missed some areas (or both!).
3. The slower the scan, the more detail can be seen, such as differences in texture.
Thus, targets that are easy to see can be found with a faster scan than the targets that blend in with the background and require the ability to see the small differences between the target and the background.
Training to scan/glance for crossing streets
When crossing streets, pedestrians must usually look both left and right to be sure it is clear to cross in both directions at the same time.
People with severely restricted visual fields can usually see the vehicles approaching from a distance, but if they look too quickly, they may miss seeing vehicles that are near to them.
What is the problem?
Vehicles that are close and coming from the right are not much of a problem because by the time the person reaches their lanes, those vehicles are gone.
The primary concern is vehicles that are close and coming from the left in the nearest lane, in what I call the "blind spot" which is about two car lengths to their left (as shown in the photo to the left).
If you start to cross when drivers are that close to you, the drivers may be unable to stop and avoid hitting you.
What is the solution?
The video to the right uses two cameras to illustrate the problem and the solution.
Both cameras, scanning at the same speed to look at approaching vehicles, illustrate that with normal vision the closest vehicles are easy to see with a quick glance, but it's not so easy to see those same vehicles with a restricted visual field.
Then we look at approaching vehicles with one camera scanning quickly and the other scanning slowly, showing that vehicles which are difficult to see with a quick glance are easier to see when scanning slowly.
So it is important that our students learn how to scan slowly enough to ensure that if any vehicle is approaching close in the nearest lanes, they will see it.
Most people who have learned how to look for vehicles effectly can learn to do it while glancing/scanning left and right with about 10-15 minutes of training as explained below.
However some students have difficulty tracking along the street accurately, and may be looking above or below where the vehicles would be.
If this is a problem, then before having them practice scanning slowly enough to see the vehicles, have them practice following the lines of the street.
If this is difficult, they may benefit from additional exercises in following lines through a large area.
I sometimes draw a thick line on a poster-sized paper, making the line loop and squiggle, with letters along the line that spell out something fun.
If they lose track of the line and accidently go to another line, they won't find the correct letters, and will need to try again.
What follows is a suggestion for training to develop the skill of scanning slowly enough to see all the vehicles:
Street that has
only one lane for traffic coming from the left (number of lanes coming from the right doesn't matter);
lots of instances where only one vehicle at a time comes from the left
(if you ask students to look and they miss one vehicle but not the others, it is difficult to debrief and find out if they saw ALL the vehicles, including the one in the "blind spot");
Ear plugs and/or headphones that block or mask sounds (you want to assess and develop their ability to see the vehicles -- their sound could provide a hint that they're there).
Before training students to scan/glance for vehicles, make sure they are able to see approaching vehicles effectively in each direction when watching steadily (without scanning).
When the student is ready to learn to scan / glance to see the vehicles, position the student facing the street.
Tell the students that you want them to face forward and, when you give them a signal, turn to the left and look, then face forward again and report whether there were any vehicles approaching.
After giving them the instructions, occlude their hearing and position yourself to watch the traffic from the left and be ready to give them the signal.
Give them the signal when either
there is only one vehicle approaching, and it's about 2 car lengths to the left (in the "blind spot") or
there is nothing coming.
When you give the signal, the students should turn to look for vehicles and then look back and report whether there are any vehicles coming.
Students should look as quickly as they can without missing any cars.
Tell them if they were correct.
If a vehicle was approaching and they didn't see it, let them know that they were glancing too fast and encourage them to scan more slowly.
If the problem was difficulty following the line of the street, practice that skill before resuming the practice in scanning slowly.
Continue to practice until the student can reliably determine if there are any vehicles approaching.
This training process is illustrated with two examples.
The first example is shown in the video to the right, which has excerpts from videos that are copyrighted by The American Printing House for the Blind (APH) and cannot be reproduced without written permission from APH.
The video captured segments of training for Barbara, who has Retinitis Pigmentosa.
Before the training, she didn't see either of the cars approaching from the left.
That was a rather dramatic experience, and you can see that when she got the feedback and realized what happened, she improved her scanning immediately. In all the subsequent trials, she was able to see vehicles that were in the same place where she had missed them earlier.
This session was very short, taking only about 15 minutes, but apparently the lesson stuck because 4 months later, she applied her scanning skills at another street.
We were very pleased that she had retained her skill and was able to scan well enough to see all approaching vehicles reliably.
The second example is another person with Retinitis Pigmentosa, as shown in the video to the right.
I did not occlude his hearing because he is deaf (Usher syndrome).
He had the same experience that Barbara did, and missed seeing a vehicle because even though he was scanning relatively slowly, it was apparently not slow enough.
You can see that after that experience he scanned even more slowly, and was able to see other approaching vehicles reliably.
[Click here to read the narration for the introduction.]
AT TWO-WAY STREETS, IN WHICH DIRECTION DO YOU LOOK FIRST AND LAST?
For people who take longer than normal to scan or glance in each direction to determine that it is clear to cross, the situation can change drastically in one direction while they are checking in another.
For that reason, once they have determined that it is safe in all directions, it is important that the last place they look before starting to cross is toward the traffic approaching in the nearest lane, to make sure it is clear in the lane that they are about to enter.
For streets with two-way traffic, that means they look to the left, and after they start to cross, they should look again to the right
because in the time that passed while looking to the left, the situation to the right may also have changed.
GLANCING TO DETERMINE SPEED AND DISTANCE OF VEHICLES:
So far, I've been talking about developing the skill of glancing / scanning to determine if there are any vehicles approaching.
Click here to find out how this exercise can be adapted to develop the skill of glancing / scanning to determine
if the approaching traffic is too close or fast to allow enough time to cross.
Since this skill uses the hearing and vision together, the training should be done WITHOUT occluding the hearing.
Training to Scan and Glance for Vehicles with Low Acuity
These videos illustrate the principles explained in Section 4 of the Self-Study Guide, Preparing Visually Impaired Students for Uncontrolled Crossings.
The first video is a simulation of what a person with low visual acuity would see and the strategy for dealing with it, and the second video shows segments of training a Deaf man with low acuity to scan reliably for vehicles.