Ah. TIA, you dangle the bait, I'll bite.   What was the result of your testing?

For myself, I think we often are aware, but I suspect that this is because we are not aware just how much we are instinctively scanning our surroundings for threats when we believe we are concentrating on something else: that we scan, don't make even fleeting eye contact, perceive no threat, so return to task at hand. If we do make fleeting eye contact we still return to the task at hand, but rescan sooner, and are alert to the possibility of a specific direction of threat, if we then make eye contact again we lock onto it, and at this point become more consciously involved.

I see this as residual "prey species" behaviour, despite our vaunted role as man the hunter.