1. I haven't eaten xxx since I lived in China. * (Past tense - grammatically you would probably say "I have not eaten XXX since living in China". This would still imply that the last time you ate the particular food was when you lived in China, but does not imply any specific timeline. However, you could also say "I used to eat xxxx when I lived in China" or similar). If I understand correctly, sentence 1 is not identical to "2. I haven't eaten xxx since I left China" Because in sentence 1, the last time of my eating xxx could have been be at any time during my residence in China. While sentence 2 implies that the last time of my eating xxx is when I ate my last meal in China or on the last day of my living in China. * (You are correct in your assumption. Statement 2 implies a more exact timing. You could say "since leaving China, I have not eaten xxxx" although this is not as exact and is similar to statement 1). 3. I haven't heard any more noise since I slept. *(Again, In English, we do not tend to state facts in quite the same way. Grammatically it is okay but unnatural. Another way of writing the same would be - "Since I went to sleep, I have not heard any more noise" or "Since I have slept, I have not heard any more noise" or "I did not hear any more noise when I slept") If I understand correctly, sentence 3 is not identical to "4. I haven't heard any more noise since I woke up" Because in sentence 3, the last time of my hearing noise could have been be at any time during my sleep. While sentence 4 implies that the last time of my hearing noise is at the last minute of my sleep. (You are again correct in your argument).