单项选择题

Thousands, perhaps even millions, of people around the world are afflicted with a neurological condition called synesthesia. The word synesthesia comes from the Greek words syn, which means "together," and aisthesis, which means "perception or sensation." Those affected by the disorder experience an involuntary, simultaneous joining of two senses; for example, some synesthetes--people with synesthesia-- perceive words as colors. Researchers do not know the causes of synesthesia, nor do they fully understand the mechanisms of the disorder. However, some scientists believe that synesthesia results from crossed connections in the brain; synapses that are traditionally associated with one sensory system have somehow crossed over into another sensory system, which leads to a juxtaposition of two, typically unrelated senses. Synesthetic perceptions are idiosyncratic, and are as varied as the perceivers themselves. Theoretically, the number of types of synesthesia is bound only by the sensory pairings themselves, such as the color/sound pairing mentioned previously. Researchers estimate that there could be as many as 35 different broad pairings-- sound/touch, taste/hearing, and so on--each characterized by many permutations and unique features. Indeed the variations could be endless, with each synesthete perceiving a slightly different color or sensation, for example. Although the perceptions vary among individuals, according to Dr. Richard Cytowic, a leading synesthesia expert, the lifelong inter-sensory associations of the synesthetes remain stable, no matter what senses are joined in a given synesthete.
According to the passage, each of the following statements regarding synesthesia is true EXCEPT