As a child, when one is building his system for recognizing people, the face normally comes in many lengths ahead of the next contender. With the face out of the contest, though, any number of contenders in the pack behind are likely to win the race. People with good hearing often include the voices of people they know in their repertoire. This is a very strong-running horse, and face blind people who are able to reliably use this clue often have the mildest effects on their lives of us all. A significant percentage of face blind people, though, do not have much success with the voice, and they must fall back on other clues, which will usually be visual.
People have different visual abilities.
So among ourselves we do often perceive the visual world differently. Some face blind see motion best, while others see things best that aren't moving. Some have great depth perception, while others see everything more flat. Some are very attuned to colors, while others can be color blind. And when it comes to the face area, some of us see a lot less than we would otherwise, just because it is the face.