Zengum! A little Engrish explanation, please

[Clodfobble]

We used to know a Thai family who had been here for decades and also spoke perfect English, but the wife admitted to me once that she'd had to brute-force memorize which words had a "sh" sound and which ones had a "ch" sound based on their visual spelling--because while she had been taught how to form both sounds with her mouth, she still could not hear the difference. If she saw "shoes" or "choose" written, she knew which word was which, but if you said them out loud, she could only rely on context.

I think your conjecture is probably right, I just thought it was fascinating that a brain could completely lose the ability to hear certain sounds. I've read that babies start pruning neurons within the first few months, including those for phonemes they never hear.