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Synesthesia: This person feels the texture of numbers and time – Science et Avenir

Some hear colors, others associate color with a letter of the alphabet. There are many ways to perceive forms of synesthesia, a non-pathological neurological phenomenon in which two or more sense organs are connected, and which is perceived by approximately 3% of the population. However, no case of synesthesia has been described so far in a person blind from birth. The first case has just been reported and studied at the University of Trento in Italy. The results are published in the journal Neuropsychologia.

“CB”, the nickname given to him in the study, is 40 years old and was born completely blind to sighted parents. Blindness due to congenital retinopathy caused by maternal rubella infection during pregnancy. With a PhD in Computer Science, CB reads Braille fluently and has no neurological or psychiatric history. CB has always said that he experiences synesthesia. Numbers, letters, days, months of the year have texture and fit into space for it. Her parents and her twin sister, also blind, had never felt anything like it.

Read alsoSynesthesia, what is it?

Velvet for the number 3, plastic for the month of April

To better describe his feelings, the researchers created a table of 40 squares of different textures and materials. For each day, month, or day of the week, the patient had to determine which texture most resembled his sensations. “These textures – different variations of paper, metal, cotton, plastic, wood – have been chosen to have a chance of matching the textures previously indicated by the subject. This is the standard task of objectifying a synesthetic experience that exists only in the imagination of a synesthete. For example, for the association of a number and the colors of the synesthete are asked to choose from the palette the color closest to what she imagines,” explains Jean-Michel Hupe, researcher at the Center for Brain and Cognition Research (Cerco, University of Toulouse and CNRS) and specialist in synesthesia. A way to approach his feelings in the most objective way. So, for example, synesthete 3 has a velvet texture, and the month of April makes you think about plastic.

A tray with 40 different textures is presented to a 40 year old blind subject. Photo credit: ROBERTO BOTTINI / NEUROPSYCHOLOGIA

In the second part of the study, a group of 10 people who were not synesthetes had to say what they think about with the same numbers, days of the week or months of the year. Neither the ten participants nor the 40-year-old synesthete were notified, and a second session was later arranged to see if they gave the same answers as the first time. “This is also a standard procedure so that the synesthete does not give random answers: after he has compiled a list of all the associations of the synesthete, he is asked to do this again much later, and without warning him that we will double-check it,” explains Jean-Michel Hupe “If the associations were made at one time, the synesthete is unlikely to remember them in a month. As he can remember a certain number, we use other participants, non-synesthetes, to have an idea of ​​the memory abilities in similar conditions. .To do the test is more rigorous, non-synesthetes are asked to remember their choice and warned that they will be tested later. The much higher identical association rate for a synesthete allows one to be confident in his testimony.”

Results: While participants without synesthesia gave the same answers only for numbers on average by 7%, a 40-year-old synesthete gave him 75% similar answers. The 40-year-old also had higher scores in other areas.

The (relative) importance of vision and colors

The authors of the study insist that vision has traditionally been a sense involved in synesthesia, which makes their findings particularly interesting. However, Jean-Michel Hupe is not surprised by the results of this study. “It is true that for many synesthetes this phase of learning is through a visual experience, most commonly colored alphabets at school, or colored magnets, or perhaps the alpha method (each letter is a symbol to help the child remember its shape). ). It is obvious that the blind man did not have all these visual stimuli in childhood.

In his study, researcher Roberto Bottini claims that 80 to 97% of synesthesia requires seeing colors. However,o present color concepts, for example vision is not a prerequisite. Colors can be imagined without seeing with the eyes. “The forms of synesthesia are very diverse, but in fact color is a very common induced property. However, this is not a matter of “vision”, strictly speaking, but of an imaginary color. The same is true for other stimuli that can induce synesthesia. “As for inductive stimuli, they can also be of a visual nature, such as reading words, letters or numbers. But most often, the synesthetic association also occurs when listening to words or even mentally reproducing them: in this case, the inductor is semantic, it is more of a concept. Some researchers have even suggested that the synesthetic inductor is in fact always conceptual.”

According to Jean-Michel Hupes, neither exceptional ability nor special power, synesthesia is sometimes too up in the air. This remains an illustration of how we can “function differently in our head.” “We don’t know, at least not yet, to determine differences in brain structure or function consistent with the experience of synesthesia.” However, this new study helps lift another veil on a neurological phenomenon that remains mysterious.

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