“Based on the Beijing dialect” does not mean “identical to the Beijing dialect.” It also doesn’t mean that the Standard can’t be spoken properly by someone with a non-Beijing accent or that someone who speaks with a non-Beijing accent can’t be expert enough to critique Standard Mandarin.
Again, would you disqualify someone with a Georgia accent or a Devonshire accent from being a judge of Standard English?
Cracks me up that people who don’t speak the language are trying to explain this.
Based on the Beijing dialect is something akin to the English spoken in NY City. Think a heavy bronx accent as equivalent to the language of Beijing Hutongs. Whereas “standard Mandarin” might be more akin to Broadway performances.
As it happens, I know what the OP is referring to and as speculated by JoeyP and others, it is indeed two sounds that English speakers lose the ability to distinguish at some low age (like 2).
The experimental setup involved babies of varying ages sitting in a chair facing a certain direct and hearing sound 1 over and over. Then sound 2 plays and a toy to their side illuminates so the child can see it and the toy moves too I think. The experiment tracks which children anticipate the toy based on the sound. Children who can hear the sound turn to look at the spot where the toy will be before the light turns on. Children who can’t only turn to look when the light illuminates.
Something something brain development something something.