In other words… how to see letters as certain colors. I soooo want to try this.
An unexpected benefit to learning synesthesia, the participants found, was a sharply rising IQ level. Study volunteers registered a stunning twelve point increase on IQ exams while a control group, who was not taught synesthesia, registered no increase. Olympia Colizoli of the University of Amsterdam, who led one study in which synesthesia was taught under laboratory conditions, said that "people with spontaneous synaesthesia also have better memories for information relating to their mixed-up senses," perhaps accounting for the apparent rise in IQ.
This isn't the ONLY kind of synaesthesia and neuroscientist David Eagleman (BTW his book is excellent) explains more in this YouTube video from BigThink: https://www.youtube.com/watch?v=FTr1VnXKr4A