Synaesthesia seems to have a genetic basis and runs in families, the genetic predisposition play a important role in determining synesthesia, but it doesn't mean that the gene is the only factor to determine synesthesia. Current studies have showed that the development of synaesthesia in different age groups, and its development follows the inverted U shape curve. A related question with developmental aspects of synesthesia is: synesthesia can be learned? Some researches have been carried out

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... e paired-association training to non-synesthetes, but there are no direct or strong evidences that the paired-association obtained from training is a kind of synesthesia. On the contrary, more and more evidences indicate that non-synesthetes after the paired-association training can not become a true synesthetes.