Challenges and strategies for scanning / glancing side to side
Pedestrians need to look both left and right to be sure it is clear to cross in both directions, but this can be difficult for some people with visual impairments. If they glance or scan incorrectly, they may miss seeing some of the vehicles.
The next page has suggestions for training students to scan or glance effectively, but first I'll explain the scanning challenges and suggested strategies for two common visual impairments:
- * Severely restricted visual field, such as with retinitis pigmentosa (RP) (using a telescope may also restrict visual fields)
* Central scotoma with loss of visual acuity, such as with macular degeneration
Severely restricted visual field
- May miss seeing vehicles that are nearby (especially vehicles in the "blind spot")
In addition to the problem with not being able to see details when scanning quickly with a small field of view, vehicles that are close are difficult for people with this visual condition to see. This is because the further that they are from an object, the more of it they can see -- illustrations of this principle are in Considerations of restricted visual fields.
The videos to the right simulate restricted visual fields. The first video shows that when glancing quickly with about 5 degrees of visual field, you can see the vehicles that are in the distance more easily than you can see those that are near to you. The second video compares glancing with normal vision and glancing with simulated visual field restriction. Both videos then show how much more effective it is to scan slowly.
NOTE: People with restricted visual fields also have problems with scanning when they cross at signalized intersections. When looking quickly to their left, they sometimes miss seeing a vehicle that is turning into their crosswalk.
BLIND SPOT:-
Although people with severely restricted visual fields might miss seeing approaching vehicles that are close, it is usually a problem only when the vehicle is in the nearest lane.
Vehicles in further lanes are usually not a problem because if they are approaching closely and are undetected when a person starts her crossing, those vehicles are likely to have passed by the time she reaches their lanes.
So there is only one place where it is extremely important that they not overlook vehicles -- a place which I call "the blind spot" for people with restricted visual fields. That place is in the nearest lane where the vehicle is so close that if they miss seeing it and they start to cross, the driver might be unable to stop -- yikes! The photo to the right shows a vehicle in the blind spot, about two car-lengths to the left of the person with the cane wearing a vision simulator.
(Click here if you want to read the scary story of how I discovered this.)
- scan slowly.
The videos above demonstrate that with a restricted visual field, when you scan slowly you can see vehicles that you missed when you scanned more quickly. Students need to learn how slowly they must scan to ensure that they don't miss seeing any vehicles in the "blind spot," as explained on the next page.
SUMMARY:
The most difficult vehicles for people with restricted visual fields to see are
in the nearest lane, about two car lengths to their left (in the "blind spot" as shown in the photo above).
The strategy to help see the vehicles better: scan slowly.
