Rikkyo University

Michiko Asano (associate professor, Rikkyo University College of Contemporary Psychology)
Kazuhiko Yokosawa (professor, the University of Tokyo Graduate School of Humanities and Sociology)

● They showed for the first time that in grapheme-colour synaesthesia, the colour that is associated with a character (synaesthetic colour) is closely linked to the pronunciation and meaning of the character, and when the knowledge a person has about the character changes, so does the synaesthetic colour.
● They conducted an experiment in which people with grapheme-colour synaesthesia whose native language was Japanese but had no knowledge of Chinese, learned the Chinese pronunciations and meanings of characters that are used in both Japanese and Chinese. The results showed that when new information on the pronunciations and meanings of characters in Chinese was added to their knowledge of the characters, the synaesthetic colours changed.
● Conventionally, it has been thought that the correspondences between characters and colours in grapheme-colour synaesthesia are stable and do not change throughout life, but their research showed that these can change through language learning. This indicates that grapheme-colour synaesthesia is closely related to language processing mechanisms that are influenced by learning.

Grapheme-colour synaesthesia is a cognitive characteristic in which the person feels that specific graphemes are associated with specific colours, and is found in 1-2% of the general population. Conventionally, it has been thought that the combinations of graphemes and associated colours (synaesthetic colours) are stable and do not change. However, a team of researchers, including Rikkyo University College of Contemporary Psychology Associate Professor Michiko Asano and the University of Tokyo Graduate School of Humanities and Sociology Professor Kazuhiko Yokosawa, demonstrated in cognitive psychology experiments that synaesthetic colours are updated when a person’s knowledge about the pronunciations and meanings of characters changes, indicating a close relationship between grapheme-colour synaesthesia and language processing. Grapheme-colour synaesthesia, a characteristic only some people have, is a phenomenon that shows how the human brain works differently in different people. The results of this research will help elucidate the mechanism behind grapheme-colour synaesthesia, and contribute to a greater understanding of the mechanisms behind the diverse ways human brains process information.

Most people around the world do not get an impression of a colour when they see a grapheme, but some associate specific graphemes with specific colours, such as rose pink with the character り (ri) or dark orange with the character と (to). This type of cognitive characteristic is called grapheme-colour synaesthesia (Note 1) and is found in about 1-2% of the general population. In the fields of cognitive psychology and cognitive neuroscience, grapheme-colour synaesthesia and other forms of synaesthesia have attracted attention as a valuable and unique resource for understanding the mechanisms of information processing in the human brain.

The colours associated with graphemes in grapheme-colour synaesthesia (synaesthetic colours) are known to have a high degree of temporal stability. For example, if someone with grapheme-colour synaesthesia says, “The character り (ri) is always rose pink,” it means this synaesthetic colour is constant and does not change for that person. Further, recent studies have shown that the pronunciation or meaning of a character often influences its synaesthetic colour. For instance, characters with the same pronunciation (such as 詩, 史, and 視, which are all pronounced "shi" in Japanese) tend to have similar synaesthetic colours, while the synaesthetic colour of the character for cherry blossom (桜) tends to be light pink, which is in line with its meaning.

If a synaesthetic colour is deeply tied to a person's knowledge (pronunciation, meaning, etc.) about a character, the synaesthetic colour should be updated when a person learns new pronunciations or meanings in a foreign language for a character they already know. However, previous studies have mostly focused on the high temporal stability of synaesthetic colours, and it has been unclear whether they could change. Therefore, one of their experiments involved having adults with grapheme-colour synaesthesia whose native language was Japanese and who had no knowledge of Chinese, learn the pronunciations and meanings for various Chinese characters they were already familiar with in Japanese.

For example, the character 祖 is pronounced “so” in Japanese, but "zǔ" in Chinese, and the character 坊 typically means "monk" in Japanese, but in Chinese its primary meaning is "street". Subjects with grapheme-colour synaesthesia were taught new pronunciations and meanings for characters, and to ensure they could recite these new pronunciations and meanings, they were encouraged to perform a memorization task for about 30 minutes. The results showed that by learning new pronunciations and meanings, slight changes occurred in the synaesthetic colours of the characters (attached figure). Such changes were not observed in characters the subjects were not taught anything new about, which indicates the changes in synaesthetic colours were the result of acquiring new knowledge about the characters. These results show for the first time that there is a close relationship between grapheme-colour synaesthesia and language processing, and that a synaesthetic colour can be updated when a person's knowledge about a grapheme changes.

The existence of grapheme-colour synaesthesia and other types of synaesthesia demonstrates the diversity of the mechanisms of human cognitive processing, as just by seeing a character, there are some people who get a sense of a colour and some who do not. This kind of diversity should be taken into consideration when attempting to gain an overall understanding of the mechanisms behind human cognition. Clarifying the mechanisms of synaesthesia through research such as this will bring us one step closer to gaining a full understanding of the mechanisms of human cognitive processing.

[Note 1] About grapheme-colour synaesthesia
Grapheme-colour synaesthesia, in which a person feels graphemes have colours, is a type of synaesthesia, which also includes sound-colour synaesthesia, in which colours are associated with sounds, and number-form synaesthesia, in which numbers are associated with certain spatial arrangements. In these phenomena, types of information that are generally not felt to be connected (e.g., graphemes and colours) are connected in a person's mind not in any deliberate way, but automatically. Synaesthesia is not a condition that interferes with daily life, nor is it a supernatural ability. The combinations of graphemes and synaesthetic colours vary from person to person. For instance, one person may feel the character り (ri) is rose pink, while another might feel it is green. The way synaesthetic colours are sensed also varies between people with grapheme-colour synaesthesia. Some people feel the colours are painted around the graphemes they are seeing, while others will not have this sense but feel an impression of the colour in their head.

・ Journal name: “Philosophical Transactions of the Royal Society B”
・ Paper title: “Synaesthetic colour associations for Japanese Kanji characters: from the perspective of grapheme learning”
・ Authors: Michiko Asano, So-ichiro Takahashi, Takuya Tsushiro, & Kazuhiko Yokosawa
・ URL: http://dx.doi.org/10.1098/rstb.2018.0349

This research was supported by JSPS KAKENHIs awarded to K.Y. (Grant-in-Aid for Scientific Research (B) numbers 26285164 and 19H01770). This research was also partly supported by a JSPS KAKENHI awarded to M.A. (Grant-in-Aid for Young Scientists (B) no. 16K17365).