THE ESSENTIAL
- About 3% of the population has synesthesia.
- There are many ways to perceive forms of synesthesia.
Researchers have just identified the first blind man able to feel the “texture” numbers and days of the week, the month of April making him think of plastic, for example. He has a rare form synesthesia, a harmless neurological phenomenon in which two or more senses are associated. For example, some may “hear the colors”, or associate a letter of the alphabet to a visual identity.
A man blind from birth
Regarding the new case presented in the journal Neuropsychologia, the patient was born totally blind to sighted parents because of rubella contracted by his mother when she was pregnant. At 40, he has a doctorate in computer science, reads Braille and has no neurological or psychiatric history.
He explained to the scientists that the numbers, letters, days and months of the year each represented a different texture to him. In order to test the veracity of his words, the researchers created a table made up of 40 squares of different materials. For each number, month, or day in the week, they asked her to determine which texture most closely resembled her feelings. “These textures – different variants of paper, metal, cotton, plastic, wood – were chosen to have a chance to match the textures previously indicated by the subject. This is the standard task for objectifying the synesthetic experience, which only exists in the imagination of the synesthete. For example, for number-color associations, the synesthete is asked to choose the color closest to the one she imagines from a palette. explains in Science and Future Jean-Michel Hupès, researcher at the Brain and Cognition Research Center (Cerco, University of Toulouse & CNRS), specialist in synesthesia.
10 witnesses
The researchers then asked a group of 10 control people to carry out the same experiment. Some time later, everyone had to start the same process again, to see if they found the same associations.
“This is also a standard procedure, to ensure that the synesthete does not give random answers: after having made the list of all the associations of the synesthete, he is asked to do it again much later, and without having warned him that we would test him again”, explains Jean-Michel Hupé. “If the associations were invented at the time, the synesthete is unlikely to remember them a month later. As he can remember a certain number, we use other participants, non-synesthetes, to have an idea of memorization abilities under similar conditions.To make the test more stringent, non-synesthetes are asked to memorize their choices and are warned that they will be retested later.The much higher identical association score for the synesthete allows to have confidence in his testimony”, he adds. Indeed, while the synesthete gave 75% similar responses to the first experiment, the participants without synesthesia topped out at 7%.