Colour is generally thought of as something experienced only by those with sight. It’s often assumed that those who’re born blind can learn facts about colours — that a banana is yellow, say — but won’t have the same complex understanding of colour that sighted people have.
But new research in PNAS from Judy Kim and colleagues at Johns Hopkins University shows that this is not the case. Instead, the researchers find that blind people have a rich understanding of colour developed through language alone.
The team looked at different kinds of knowledge about colour in both sighted (N=19) and congenitally blind (N=20) participants. The research was split into three distinct experiments:
The first aimed to probe causal-explanatory and associative memory knowledge of real objects’ colours. Participants were asked to generate common colours for 54 specific objects which were either natural (e.g. strawberry) or artificial. In this latter group, the colour of some objects served a purpose (e.g. stop sign), but for others did not (e.g. book). Participants also indicated whether two of the same objects would be likely to have the same colour.
In experiment two, participants were asked to make inferences about colour consistency in novel natural and artificial objects in an “imaginary island scenario”. Participants were asked to imagine having discovered an undocumented civilisation on a remote island, complete with all that culture’s unknown objects; for example, green “Enly” gems, used for power, and yellow “Kanpa”s, used to spray odorless chemicals in the home. As objects were presented, participants were asked to guess how likely the next such one they come across would be the same colour. This task assessed the extent to which participants believed that objects within the same category (i.e. natural or artificial, with or without functional colour) would also share a colour. These beliefs would indicate that participants were able to build generalisable theories about why objects had certain colours that could be applied more widely.
The final experiment was more open ended; participants were asked to provide explanations as to why particular objects have their colour (eg. “Why is a carrot orange?”), and were able to give any reasons they thought to be correct. This provided further insight into the specifics of both groups’ knowledge about causal mechanisms of colour.
Some findings were consistent with the idea that colour knowledge is acquired through sight. For example, blind people were less likely to agree on associative colour facts; when asked to generate a common colour for a banana, only 50% of blind participants said that bananas were “yellow”, compared to practically all sighted participants. This would suggest that, at least in some cases, directly seeing the colour of an object is more informative than acquiring facts about its colour through other means.
However, both groups agreed more on the likely colour of both natural and artificial objects with functional colours than artificial objects whose colour served no purpose. Both blind and sighted participants also expected two natural objects (e.g. two strawberries), or two artificial objects with functional colours (e.g. two stop signs) to share the same colour, but believed it less likely that two artificial objects whose colour served no purpose (e.g. two books) would have the same colour. Similar findings were observed in the imaginary island scenario, even though neither group had ever seen the novel objects (e.g. “Enly” gems and novel cleaning devices) described in this vignette.
When it came to providing explanations of why object colours differed, the groups were also relatively similar. For natural objects, around a third of sighted and blind participants said that “it just is that way”, and a similar number appealed to processes to explain colouration; for example, describing how photosynthesis makes plants green. When it came to artificial objects without functional colour, both groups commonly explained that colour depended on aesthetic choices (64% vs 44%), or referred to the material from which the object was made (18% vs 13%). And finally, for functionally coloured objects, about half of both groups explained that the colour was the result of cultural convention, and a quarter of both groups said that a specific colour was used to make the object more visibile.
This study wonderfully illustrates that blind and sighted people share common knowledge about colour. Though the two groups differ in some domains — particularly when it comes to associative knowledge about the colour of objects (eg. bananas are yellow) — they are largely similar in their understanding of the natural occurrence and application of colours. Blind individuals are able to draw upon deep understandings of how colours function, and make inferences about totally new objects based on their category alone, in a way that closely resembles those with sight.
The authors take this data to suggest that those living in the same wider societal culture, sighted or blind, develop similar intuitive theories of colour which can be applied to totally novel situations. The source of this knowledge is almost certain to be linguistic, and future research may determine at what ages this framework for colour knowledge develops in both sighted and congenitally blind individuals.
Emma L. Barratt (@E_Barratt) is a staff writer at BPS Research Digest