Adults Can Be Trained to Acquire Synesthetic Experiences

Fourteen non-synesthetic adults completed a structured training regime — roughly 30-minute sessions of 4–5 adaptive memory and reading tasks, five days a week, for nine weeks (~24 hours total) — designed to reinforce 13 specific letter–color associations. They were compared against a control group on a battery of behavioral and physiological tests before and after.

• ▸After training, participants showed standard behavioral and physiological markers of grapheme–color synesthesia, including synesthetic Stroop effects and skin-conductance responses.
• ▸Many participants reported color-like experiences for black letters during the training period — though these were often described as somewhat voluntary, not the fully automatic, involuntary percepts of lifelong synesthetes.
• ▸Honest caveat: the subjective experience was largely transient. Follow-up work found it faded in the months after training stopped, even though the automatic association lingered — i.e. it was not a permanent change.

This is the best evidence that association-based training can reshape perception-linked responses in adulthood — the same principle Chromesthesia applies. Two honest limits: the strong evidence is for letter→color (sound→color is a reasonable extension, not an identical proven result), and effects build with, and depend on, continued practice.