Irrespective of whether or not wearing headphones meaningfully reduces your ability to hear what is going on around you, and whether that would matter if the infrastructure was better, I'm also a bit surprised that no one has ever investigated it.
Chalk it up as another example for the sociology of unsubstantiated Political claims. (Known knowns, known unknowns, unknown unknowns and politically expedient suppositions about minority outgroups.)
Pete
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