Our ability to tell colours apart may not depend on language: Case study

The human ability to categorise colours may be independent of language, according to a case study on a 54-year-old French-Portuguese man who specifically lost his ability to correctly name colours after suffering a stroke.

The ability of the man, identified as RDS, to categorise colours based on hues has remained intact since he suffered the stroke in 2014.

The case study, published in the journal Cell Reports, looked at how language influences human thinking. For centuries, philosophers have tried to understand if learning the names of objects was important for categorising them.

"We perceive colours as continuous. There is no sharp boundary between, say, red and blue. And yet conceptually we group colours into categories associated with colour names," said Paolo Bartolomeo, a neurologist at the Brain and Spine Institute in Salpetriere Hospital in France.

Many scientists, according to the study, believe that the names of different colours are stored in the human brain's left hemisphere, and for categorising colours, one is dependent on brain activity in that region.

However, the RDS case study suggests that colour categorisation is distributed across both hemispheres of the human brain.

In the study, RDS was asked to identify same-category colours in viewing discs. These contained two colours from the same category, such as indigo and blue, or from different categories like brown and red.

RDS was also asked to name 34 colour patches that were presented on a computer screen, of which eight were achromatic -- white, black and grey -- and 26 were chromatic.

He was able to name all colours normally before the stroke. However, post the brain injury, an MRI scan revealed a lesion in the left region of his brain.

To ensure that RDS' brain was not an abnormal case, the researchers compared the functioning of his unaffected brain regions to that of the same areas in healthy subjects, and developed a non-verbal test to categorise colours.

"Our result -- that his colour categories were independent from language -- could be generalised to healthy adults," Bartolomeo said.

The researchers noted that the lesion could have severed RDS's memory of colour names from his visual perception of the colours.

RDS could successfully group most colours -- even those he couldn't name -- aptly into categories such as dark or light, or as being a mixture of other colours, the study found.

"We were surprised by his ability to consistently name so-called achromatic colours such as black, white, and gray, as opposed to his impaired naming of chromatic ones such as red, blue, and green," said PhD student Katarzyna Siuda-Krzywicka, the first author of the study.

The study also suggests that our language system may process non-chromatic colours like black, white, and gray differently from chromatic colours.

This raises questions about how different signals related to colour from the environment are segregated and assembled in the human brain, Siuda-Krzywicka said.

Commenting on the research, SP Arun, Associate Professor at the Centre for Neuroscience at the Indian Institute of Science (IISc) Bangalore said that it is still not clear from the study if the patient's problem in naming colours was due to an inability to distinguish between colours.

"From the study, we can see that the patient was able to name brighter colours more accurately than lighter and intermediate colours. This could happen if someone loses colour sensitivity.

"Thus, the patient may not have a problem only in naming colours but may have problems discriminating between colours," said Arun, noting that the study might need further scrutiny.