There is a very peculiar "habit of the mind": synesthesia, a condition in which a stimulus characteristic of a sensory modality promotes sensations characteristic of other senses. One person every 2 thousand experience this condition in a particularly acute way although 1 out of every 300 have a less marked variant.
Different types of synaesthesia can be found, the first condition described in the scientific literature was discovered by Francis Galton and is called grapheme-color synaesthesia. People who suffered from this condition when faced with numbers or written letters could see specific colors. Richard Feynman, winner of the Nobel Prize in Physics said he could see the equations in colors.
Wassily Kandinsky, well-known impressionist artist, saw colors when he listened to musical tones. Thus, he tried to use this amalgam of senses to paint unique paintings where he expressed the visual equivalent to a symphony of colors.
Actually the surprising cases of synesthesia are many, now we will try to approach the why of this strange phenomenon.
As you can imagine most of the explanations seek the path of neurobiological mechanisms. One of the theories states that synesthesia is the result of unusual connections between different sensory regions of the cerebral cortex due to inadequate processes that took place during the development of the nervous system. Thus, the stimuli that would be designed to be decoded by a single sensory system generate an activity in other systems that evoke the synesthetic sensation. Thus, this theory asserts that the difference between a synaesthetic brain and a non-synesthetic brain is merely functional, not anatomical. New research based on Neuroimaging reaffirm this idea as they have been able to see that in the brains of the synaesthetic people there is a coactivation of the main area responsible for processing the stimulus and the adjacent regions, which suggests that this inappropriate interaction is the cause of experiencing sensations inadequate before stimuli.
Researchers from the University of Amsterdam have also come to the conclusion that these connections differ in their intensity. Thus, some people who present inadequate responses to graphemes (called projectors) can see colors related to letters or numbers while other people (called associates) only have the experience of colors at the mental level. As you can imagine, the projecting people present a connection between the areas (specifically between the v4 area and the fusiform gyrus) stronger than the associating people. However, it is not yet known if this connection strength is due to an increase in myelin in the axons or simply because there is a higher axonal number.
In the search for another explanation and moving away from the neurobiological theory, researchers from the University of Waterloo have asked if there is any peculiarity of graphemes that can be related to colors. The study involved 55 people suffering from grapheme-color synaesthesia and 254 non-synesthetes.
The participants had a monitor with color palettes where 36 graphemes appeared (from letter A to Z and from figures 0 to 9). The task was very simple: they had to position the mouse in the color that came closest to the one that evoked in their minds the grapheme they observed on the screen.
The results revealed that increasing the frequency of grapheme use also increases the luminosity of the color that is systematically associated. Thus, there is a relationship between the basic characteristic of color (luminosity) and a characteristic of grapheme (the frequency of use in everyday life). The most important conclusion is that this relationship is not only evident in synesthetes but also in non-synesthetes. In other words: each one of us would show a tendency similar to associating a more luminous color to the most frequent graphemes although this association does not take place consciously and does not constitute a concrete perceptual experience.
This research provides a very suggestive idea: grapheme-color synaesthesia is related to the learning of grapheme and, above all, it is a reality related to our normal cognitive processes.
However, neurobiological and social theories are not exclusive but complement each other. In this way, synesthesia would have a social conditioning related to our learning and how we use colors and graphemes on a daily basis while certain peculiarities at the cerebral level would activate the perception of the synesthetic experience.
