An NPR portrait of a very rare problem, phonagnosia, or voice blindness:
According to phonagnosia researcher Diana Sidtis, the part of the brain that allows people to distinguish things like age, gender and emotional content in a voice is different from the part of the brain that makes sense of whether or not the voice they’re hearing has “personal relevance.” That’s the part of the brain that’s able to relate to a voice and determine that it’s actually familiar.