I'm having a strange experience trying to reproduce a token of ɛ / æ from a native speaker of Thai. When I play my attempt back it sounds like a reasonable copy, but looking at it in Praat, the formants are quite a bit off. With some experimentation I can produce a vowel with similar formants, but it doesn't sound like the original token. This would seem to indicate that I'm latching onto something other than the formants in the original, that that quality is present in my initial attempt to copy the sound but not my later attempt to reproduce the formants, and that it's throwing my perception of the formants off... but what could it be?
Is there any research into the perception of foreign language sounds that might cast light on how the perception of vowels can be distorted by factors like (say) nasalisation or voice quality?