Persistence of Vision

One strange thing I've noticed along the way is how long the images of people I meet stay with me. As I ride I think about the chance encounters that have taken place and the faces are crystal clear in my mind. This morning I was thinking about someone I talked to on day 2 and it is still so clear. Is this an effect of being alone such a large part of the time? Is it a natural human response to the nomadic life, or is it just me?