Quite a leap to diagnose such a condition over the internet. To me it just seemed like a bad example. His second example works though, if you try to force a visualisation in your mind:

"Another common example is the visual representation of the full year with four seasons"

True, I should say the author "may" have Synaesthesia. But the spacial appearance of a number line is an absolutely textbook example of it. The interesting thing about his choice of example is that's what he perceives and he assumes everyone else also has a spacial representation of numbers.

Most Synaesthestes don't realise there's anything different about their thinking until they hear about the condition. So, I just wanted to make the author (and others) aware of it for their interest.

Synesthesia proper is a whole other level than merely visualising abstractions (which tons of people do, if not everybody)...

It's a spectrum sure and sound/taste effects would be lot more difficult to deal with.

We all visualise abstractions, but adding fixed, and arbitrary, properties (the number line turning at 20) is different and more akin to:

https://en.wikipedia.org/wiki/Number_form

> I recall from very young period of my life that in our kindergarten there were numbers in a cloakroom, written along the wall, and number 20 was exactly at the corner.

Maybe this is why and not Synesthesia?

Childhood experience is thought to be one of the 'causes' of Synesthesia. For instance people who perceive letters as having colours (a is always red, b is blue), often find that these correspond to the colouring of alphabet fridge magnets or toys they had as children.

COoL!

I have tremendous trouble reading a list of color words on a whiteboard, if each is written in a different color from what the word is. E.g. write blue in black; write yellow in red; write red in blue etc.

Extra points - try to say what the color each word is written in, while looking at them. Maybe even harder.

That's the "Stroop effect"