Well, you know, I'm Canadian, which means I speak North American English (NAE).
Originally Posted by LordJenkins
In North American English, all the <t>'s in your list, with the exception of the <t> in mental and dental, are pronounced as flap D. For example,
bottle - bo[D]le <[D] sounds just like [d], but quicker>That dental and mental, which have a phonetically lateralized /t/, are exceptions has to do with what's sitting in the preceding syllable's final slot, also known as the coda. Compare:
- me'[D]al / me'[tl] <both are NAE>
As you can see, the preceding coda in men'[t]al is filled by /n/, whereas it is empty in me'[D]al. Both forms, CVC'CVC (i.e., men'[t]al) and CV'CVC (i.e., me'[D]al), have primary stress on the vowel in the 1st syllable, which means stress isn't a factor determining /t/'s pronunciation. The determining factor appears to be the coda, and whether it's empty of filled:
That <t> in metal is pronunced with lateralization (i.e., me'[tl]) has to do with the phonological make up the lateral /l/: it's a liquid, you know, and as such is privy to vocalization, which in other terms means it is vocalic-- just like a vowel, you can sing it. The result is this: the 2nd vowel in metal is dropped and /l/ becomes vocalized: it takes the vowel slot.
/t/ is realized as flap [D] or as [t] if the preceding coda is empty:
- metal is pronounced me'[tl] wherein [l] is vocalic, not consonantal.
In short, when /l/ becomes vocalic its features bleed over to /t/, making /t/ sound lateralized. The process by which a sound takes on the features of an adjacent sound, specifically an immediately following sound, is called Regressive Assimilation:
- /t/ becomes [tl] before [l]
You may want to read this article: WHAT IS PHONOLOGY