No, I do think it is impossible to develop actual synesthesia as an adult. The impossible part is having a permanent result.
Studies have tried to mimick the experience by letting people for example read letter-colored books. The results often differ but even if the subjects experience some type of synesthetic experience, it is always short lived.
I do like the brain plasticity argument but it unfortunately doesn’t often hold because the thing with brain plasticity is that the brain is also inclined to go back to the way it was.
But this thread was about fogelmemory and his claim of having synesthetic experience.
We already know that a permanent result of synesthesia training has never been observed and that you either develop it as a child or get it through a brain damaging accident.
He didn’t mention having it in his youth and he didn’t say he was practising for synesthesia either.
However he did mention he had some mental illness in the past. I don’t know about the effects of it on the brain but that is the only way he perhaps could’ve developed synesthesia, on “accident” I guess.
He should see a professional if he wants to know for sure. It’s often very easy to test if your synesthetic experience is real by looking at the consistency and looking at your physical reactions during your synesthetic experience.
If I see multiple digits of the same number like 333 or 269993, I often feel uncomfortable and sometimes even cringe. It bothers me on a physical level. Those numbers are often harder for me to memorize but for other people those are the easiest.
While I am typing this, I am changing my mind about fogel’s synesthesia claim. It seems to really bother him which is a big sign of synesthesia.
4 years ago I had an autistic meltdown. My senses where overwhelmed and an ambulance and everything had to show up.
The trigger of my meltdown was actually my synesthesia.
I mentioned before how people with synesthesia often have synesthesia in multiple areas. I also have some synesthetic experience for random no-text images. This experience is often much intenser than my feelings for numbers. Stock photo’s and car commercials are the worst.
If fogel’s experience is that bothersome to him, I advice him to seek help. It can turn really bad.