Every time a siren shrieks on the street, our conscious minds might ignore it, but other brain regions behave as if that siren were a predator barreling straight for us.
It's worth mentioning that a siren is specifically meant to pull your attention. It's not really the same as a constant background susurrus.
I work in the heart of a city, and there's a constant babble of traffic and pedestrians a few floors below. That's fine and can be tuned out - the noise that's distracting me from concentration is random loud office noise. Noise that can't be filtered out as 'background'.
It's worth mentioning that a siren is specifically meant to pull your attention. It's not really the same as a constant background susurrus.
I work in the heart of a city, and there's a constant babble of traffic and pedestrians a few floors below. That's fine and can be tuned out - the noise that's distracting me from concentration is random loud office noise. Noise that can't be filtered out as 'background'.