pudding cat Wrote:I'm a bit confused as to why people would get vowel lengths wrong because obviously if you can read the word you can see how long the vowels should be. Is it linked somehow to mispronunciation of vowels?Just because you know the written form of a long vowel doesn't mean you're going to flawlessly hit the 1.5-2 mora range every time you attempt to pronounce one. It's not a question of remembering the difference between と and とう, but a question of timing. You may still pronounce it as a long vowel, but if it falls outside the range natives maintain, it's going to sound like you have an accent. People do a similar thing with ん, generally shortening it instead of giving it a full mora, which makes something like せん sound more like a syllable than two mora. If your vowels aren't enunciated properly it may affect the length too, or at least the perceived length, as vonPeterhof was describing.
Perfecting mora rhythm in particular is no easy feat for somebody who grew up using syllables, so I have to disagree with nadiatims' suggestion that it's only a problem for beginners, especially since it's yet another thing that can go unnoticed indefinitely if the learner doesn't have the proper awareness. Try seeing how uniform the length of an intermediate student's vowels are in a word like 重症急性呼吸器症候群.
I don't think you can underestimate the influence of your first language when you're speaking freely. Even my Chinese friend who's studied since she was a teenager (5 years in Japan) was off a few times when we met. Clearly, it's nothing for her to worry about, but it shows you can't take anything for granted when you're relying on your English/Chinese/Russian-speaking brain to unconsciously produce a flawless Japanese accent.

, or it doesn't matter.
I'm one of those learners who really only became aware of pitch after years and years of studying Japanese. I felt confident about my pronunciation, but one time after giving a speech in class, my teacher handed me a sheet where she had marked everything I had gotten the intonation (not pronunciation) wrong on... I was shocked :O There were so many areas!