Telling green from blue with NIR spectroscopy

How do we know that an object is green or blue, when there are many different shades of green and blue? Do we instinctively know or does our ability to group objects into different distinct colours develop with our language; do we need to watch others describe objects as green or blue before we can do so ourselves? This question has troubled first philosophers and then scientists for centuries, but now NIR spectroscopy may have finally helped reveal the answer.

A team of Japanese researchers led by Jiale Yang at Chuo University in Tokyo used functional NIR spectroscopy to investigate how the visual cortex in very young infants responds to different colours. Because these infants hadn’t yet learned to talk, they obviously couldn’t understand what the terms ‘green’ and ‘blue’ meant. So if their visual cortex responded differently to these different colours, their ability to distinguish between them must be innate.

Yang and his colleagues strapped a head band containing 12 NIR sensors to 12 healthy infants, between five and seven months old, with the sensors grouped at the back of each infant’s head, covering the visual cortex. They then used the NIR sensors to measure changes in the concentration of oxygenated haemoglobin in the visual cortex, as a measure of neural activity, while showing the infants two sets of geometric figures. In one set, the colour of the figures alternated between blue or green; in the other set, they alternated between different shades of green.

The researchers found that the concentration of oxygenated haemoglobin in the visual cortex increased when the infants were shown the different coloured figures, but stayed the same when they were shown figures that were different shades of the same colour. As they report in the Proceedings of the National Academy of Sciences, this indicates that the ability to distinguish between different distinct colours is innate, although this ability may well be modified by language. Interestingly, Yang and his colleagues found the same change in haemoglobin concentrations when they showed the figures to adults as well.

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lerud's picture

Could this chemical change in the brain be linked to why we have an emotional response to colors?