From what I have read, the approximant /j/ (which used to be called a semivowel) in a word starts with something very like the vowel /i/ and quickly glides to the vowel after it. I can understand how this can work in words like "yes". But in "yeast", the vowel after /j/ is already /i/, how can it glide from /i/ to /i/?
I'd like to ask native speakers, do you feel a glide when saying "yeast"? If yes, in what direction is the glide? Thank you very much!