I think it’s possible to train yourself to have synesthetic-like responses. You might be interested in the threads below.
- Study: Synesthesia Can Be Learned
- Can Synesthesia Be Learned?
- Synesthesia Training Program (Letters and Numbers)
- Synesthesia training for grapheme synesthesia
- New Insights Into Synesthesia
- Synesthesia Color Chart for Letters
- Alexander Scriabin and Artificial Synesthesia
I tried to associate the vowels in my number system to angles by running through them with hand movements, and I found that after a while I associated those sounds with the angles. 4/A goes down. 8/EI goes to the right, dipping down a little, etc. I think I already have some natural association between some ideas and angles/space, but I intentionally created those ones for my number images.