I've done experiments on my friends and myself, and when listening to chords, the note we end up hearing at the forefront (in other words the note we hum when reproducing the song) is actually the highest note in the chord. For example, in the C major chord of C,E,G, the note that will be hummed is G. I looked online to see if anyone else has the experience, and there appears to be a lack of information. Some people said that they guess you should head the root/dominant note (C in our example), but all my tests have shown otherwise. Is there any research that has been done about this, or anyone with different experience?
As a generalisation, the note heard best is often the highest being played. So, it will depend greatly on which inversion is being listened to. I suspect so far, as intimated from the question, that it's the root version being played. So no great surprise that the 5 is spotted. think about it - if you were harmonising a melody on, say, piano, you'd be putting the melody notes on top of the harmonies. that's because we tend to hear the highest notes better. If we lost that melody note inside the harmony, we wouldn't be hearing the tune we're supposed to.
The other end of the spectrum is also valid. In a full-blooded chord with maybe 6 or 7 notes, the lowest will quite often be the root - played by a low sounding instrument - maybe bass. Making it a root version, regardless of what's above. That note defines the chord best. In a C major or C minor, it's still that C. It's what I listen to initially when transcribing chords as it's going to be the first part of what I write down.
Well, as an example, play A2, A3, E4, A4, C♯5, E5, and G5 all at once. You can hear the other notes, but more likely the chord will sound like an A. So sometimes, it's definitely the root, other times it would depend, like for diminished 7th chords or any other chord in a context where it's easy to pick out individual notes.
It is the top pitch(highest note) that is heard normally.
Example) If all four voices in SATB are singing, Soprano is heard and hummed clearly compared to the other voices. Similarly with the C chord, G is the most heard/hummed note. However the Chord name or chord root note is the fundamental main note which is being supported/harmonized by the other notes (3rd note supports the root note's major/minor quality similarly 5th note harmonizes the root note), in other words we hum the top note to support the root note.