Synesthesia: This man feels the texture of numbers and time

Some feel colors, others associate a color with a letter of the alphabet. There are many ways to perceive the forms of synaesthesia, a non-pathological neurological phenomenon in which two or more senses are associated and which is perceived by about 3% of the population. However, until now, no cases of synaesthesia have been described in a person blind from birth. A first case has just been reported and studied by the University of Trento in Italy. Results published in the journal Neuropsychology.

CB“, nickname given to him in the study, he is 40 years old and was born totally blind to his sighted parents. Blindness due to congenital retinopathy caused by the mother’s contamination with rubella during pregnancy. With a PhD in computer science, CB reads braille. fluent and has no neurological or psychiatric history. CB has always said he experiences synaesthesia. Numbers, letters, days, months of the year have consistency and fit the space for him. His parents and twin sister, who is also blind. , I’ve never experienced anything like it.

Read alsoSynesthesia, what is it?

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

To better circumscribe his feelings, the researchers created a table made up of 40 squares of different textures and materials. For each number, month, or day of the week, the patient had to determine which consistency most resembled his feelings. These textures – different variants of paper, metal, cotton, plastic, wood – were chosen to have the possibility of combining the textures previously indicated by the subject. This is the standard task for objectifying the synaesthetic experience, which exists only in the synaesthete’s imagination. For example, for number-color associations, the synaesthete is asked to choose the closest color to the one she imagines from a palette.“, Explains Jean-Michel Hupès, researcher at the Brain and Cognition Research Center (Cerco, University of Toulouse & CNRS) and specialist in synaesthesia. A way to get closer to his feelings, in the most objective way possible. So, for example, for the synaesthete, 3 has the texture of velvet, and the month of April suggests plastic.

The tray with 40 different textures presented to the 40-year-old blind subject. Photo credit: ROBERTO BOTTINI / NEUROPSYCHOLOGIA

In a second part of the study, a panel of 10 people who are not synaesthetes had to say what the same numbers, days of the week or months of the year make them think. Neither the ten participants nor the 40-year-old synaesthete were notified and a second session was then organized to see if they had the same answers as the first time. “This is also a standard procedure, to ensure that the synaesthete does not give random answers: after having made the list of all the associations of the synaesthete, he is asked to do it again much later, and without having warned him that we would try it. new one”explains Jean-Michel Hupé. “If the associations were invented at that time, the synaesthetes are unlikely to remember them a month later. Since they can remember a certain number, we use other participants, not synaesthetes, to get an idea of ​​their memorization capabilities under similar conditions. to make the test more rigorous, non-synaesthetes are asked to memorize their choices and are warned that they will be re-examined later.The much higher identical association score for the synaesthetes allows them to have confidence in their testimony.

Results: While participants without synaesthesia only gave the same answers for numbers averaging 7%, the 40-year-old synaesthete gave them 75% similar answers. The 40-year-old also scored higher in the other domains.

The (relative) importance of sight and colors

The study authors insist that sight has traditionally been a sense involved in synaesthesia, which would make the results of their study particularly interesting. However, Jean-Michel Hupé is not surprised by the results of this research. “It is true that for many synaesthetes this learning phase passes through a visual experience, most often that of colored alphabets at school, or colored magnets, or perhaps the alpha method (each letter is a character, to help the child to memorize its shape). Obviously, a blind person did not have all of these visual stimuli in his childhood.This experience, however, shows that sight is not actually a necessary sense for synaesthesia.

In his study, researcher Roberto Bottini states that between 80 and 97% of synaesthesias require the sight of colors. However, por imagining concepts of color, for example, sight is not a prerequisite. Colors can be imagined without being seen by the eyes. “The forms of synaesthesia are very different, but in fact color is a very frequent induced property. However, it is not a question of” sight “in the strict sense, but of imagined color”. Ditto for other stimuli that could trigger synaesthesia. “As for inductive stimuli, they can also be of a visual nature, such as the reading of words, letters or numbers. But most of the time the synaesthetic association will also be made by listening to the words, or even by their mental evocation: in this case the inductor is semantic, it is rather the concept. Some researchers have even proposed that the synaesthetic inductor is actually still conceptual. ”

Neither exceptional faculties, nor special powers, synaesthesia is sometimes too pending according to Jean-Michel Hupès. It remains an illustration of how it can be “they work differently in our head. ” We do not know, at least for the moment, to identify differences in the structure or functioning of the brain corresponding to the experience of synaesthesia.This new study, however, helps to lift an extra veil on this neurological phenomenon, which remains mysterious.

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