What sound did your brain refuse to hear when you started learning a new language?

There are tons of videos online where the same audio suddenly sounds like two completely different phrases depending on what word you look. For example: “green needle” / “brainstorm.” The recording doesn’t change — what you hear does.

In 1976, Harry McGurk and John MacDonald described a related effect. Participants watched a video of a speaker saying one syllable — for example “ga” — while the audio played a different one — “ba.” Many listeners didn’t report hearing either of them. They heard "da" instead.

Now I’m dealing with my own version of this. I just wanted to learn to read Hangul.

ㅗ / ㅜ
ㅔ / ㅐ
ㅖ / ㅒ

These are different vowels and should sound different. Right? But why do they collapse into the same thing in my ears? Why do I replay them again and again and still hear the same sounds? 🤯

I just don’t trust my ears anymore.