Our brain interprets colours that are close to each other in the spectrum as the same… so orange and purple colours side by side will often be perceived as red by our brains.
Only when we seen them in isolation will we see the actual colours. They only appear more or less equally red because your brain is interpreting them as red lit by either yellow or blue light. This kind of misperception is an example of perceptual constancy, the mechanism that allows you to recognise an object as being the same in different environments, and under very diverse lighting conditions.
There are many indications that constancy effects must have helped us survive (and continue to do so). One such clue is that we are not born with perceptual constancy, but develop it many months after birth. So at first we see all differences, and then we learn to ignore certain types of differences so that we can recognise the same object as unchanging in many varied scenarios. When perceptual constancy arises, we lose the ability to detect multiple contradictions that are nevertheless highly noticeable to young babies.
In a study published last December in Current Biology, a team of psychologists led by Jiale Yang, of Chuo University in Japan, found the exact opposite for infants of up to three-four months of age.
The scientists studied how 42 babies, aged three to eight months, looked at pairs of images rendered from real 3D objects. Because infants cannot describe what they see, the team measured how long the babies looked at each image. Previous research had shown that babies look for longer times at novel objects than at objects they are familiar with. This meant that the scientists could know, based on how much time a baby spent on an image, if she thought that image was similar to, or different from, the previous picture. If the baby spent less time looking at the second image than the first image, it indicated that she thought she had just seen the same image before (she was bored by it, so she didn’t need to look at it for very long). But if the baby looked at the second image for an equivalent time to what she spent on the first image, it indicated that she found both images equally interesting and surprising.
The data revealed that, before developing perceptual constancy, three to four month-old babies have a “striking ability” to discriminate image differences due to changes in illumination that are not salient for adults. They lose this superior skill around the age of five months.
During the first year of life, infants suffer the loss of a myriad discriminatory powers: Among them, the ability to recognise differences in monkey faces that are hardly detectable to adult humans, and the ability to distinguish speech sounds in languages other than spoken by their own families. Objective differences become subjective similitudes.