No, but it's very hard to learn to make contrasts between pairs of sounds that aren't distinguished in your language.

That is, it's hard to add new phonemic buckets.

/l/ and /r/ is a classical example, of course, but there are lots of other challenges, like English having so many more vowels than Japanese.

Japanese /a/ encompasses a number of English vowels.

So they have to split one phonemic bucket up to hear those as different sounds in English.

Japanese learners of English do frequently substitute /s/ for /θ/ (th as in moth) and /z/ for /ð/ (th as in mother)

So I think it's a challenge all around adding new phonemic buckets

Well, sure, it takes time and effort to learn. But the original cause is that native speakers of any language are trained since birth to be very efficient at processing their own language, and so they don't pick up on contrasts that aren't present in that language. Part of being very efficient at processing your native language is throwing away useless information.

Um, I don't know. I've been kind of overwhelmed with stuff this week! :-)

Oh, what's your native language?

I'm a native speaker of English, so I've got 14 . . .

Finnish is a neat language! :-)

It's possible for Japanese speakers to mishear the th sounds as t and d

I don't know. Perception is really complicated.

If you're interested in the psycholinguistics underlying all of this, I highly recommend Native Listening

amazon.co.jp/Native-Listening-Language-Experience-Recognition/…

Oh!