"I am reasonably sure that I am a synaesthete. I have always perceived the week as an oval and the year as a circle."
Me too! I've tried explaining this to other people, and they always look at me like I'm crazy.
I also have a really good memory, and am good at placing dates. I think the reason is that I can place them on my visual circular calender.
Edited to add:
Just looking at this article, and this is completely how I think:
"For example, some see the months of the year in a running track shape, with, say, August and September taking up most of the right-hand side and the rest of the months squashed on the left." "People who experience a visual week or year are often able to use this information to recall times and dates extremely well."
So I guess my hypothesis was correct.
This is fascinating!