It's doubtful we could function well (or at all) if this filtering mechanism were not in place.

Indeed, this inability to filter input seems to be one of the foundations of the pattern of disabilities we label "autism." People with autistic spectrum disorders seem to be unable to ignore sensory input, no matter how repetitive or trivial, and their perceptions also seem to be more sensitive. For instance, many autistic people are overwhelmingly distracted by fluorescent lights, because they can see the lights flicker, even though people of normal perception cannot detect the rapid flicker.