I assumed a correlation between the people on my commute and wearing headphones. They all have headphones on, but none of them check their surroundings, which I assume would be due to the fact they are lost in the sounds of music. Also, it does not appear they are looking ahead in a manner to keep them from being hit, but more like a thousand-yard stare. They also fail to acknowledge me when I approach from behind, even when I say "to your left!" as I pass.

Everyone else I pass without headphones seem to acknowlege their surroundings, more so than their headphone-counterparts. Also, it makes me less wary of passing them because they tend to give me acknowledgement when I say "on the left!"