A light touch: colour, surface, texture

Dr Shelley James

Notes from Light Tribe Webinar with Phos, 6 May 2020

It’s impossible for a sighted person to conceive of a world without colour - it seems to be such a stable and ‘real’ dimension of experience that it’s hard to believe that it is entirely generated by our brain.

Think of it like the vivid pictures we see from the Hubble Telescope. The colours here are completely ‘false’. There is no telescope yet devised that can capture the swirling energy in those dark galaxies and produce a coloured image. Scientists have simply assigned colour values to this data. And that translation makes it possible to ‘read’ that patchy stream of signals as a bright and coherent structure in space. And because they all use broadly the same system across different data sets, we can compare and contrast different views and track change over time.

Those colours are entirely ‘false’ - as are the colours you are ‘seeing’ on your screen right now. But that does not make them any less useful as a way to gather reliable information about the world.

When we say a leaf is green, we actually mean that it is anything BUT green. Packets of photons or ‘light’ are thrown out by a source, such as the sun, and strike the surface of the leaf. The surface absorbs everything except the green wavelengths and the rest is reflected, to be gathered by your watchful gaze.

Light-sensitive cells lining the back of the eye translate that stream of photons into a pattern of signals that are in turn interpreted through a sequence of connections in the brain - a bit like the Hubble data set.

A complex cascade of reaction ripples out from that photon-fall - from the autonomic nervous system that regulates digestion and pupil dilation to the language processing centre reaching for the word ‘lettuce’. Knowing that we are looking at a lettuce leaf means that we are remarkably forgiving about the wavelengths that we actually need to ‘see’ in order to read the colour green. This is a phenomenon called ‘colour constancy’ - when we know what colour something ‘should’ be, we assign that colour even when, objectively it is not.

Think of seeing a friend wearing a white t-shirt in a UV-lit disco. You still think of it as white, even though, when you take a selfie, it looks blue. That’s because the only wavelengths of light striking that t-shirt are blue - so that’s what comes back.

Until recently, we thought that colour vision was all about our ability to see coloured objects in the world and that all those cues were processed through the visual cortex. But that did not explain why different coloured lights had such a profound effect on our physiology.

It turns out that there is a parallel, ancient pathway that is connected directly to the central nervous system. These specialist cells are tuned to notice changes in the wavelengths of light along the blue-yellow spectrum. This corresponds to sunlight at different times of the day - from the warm glow of sunrise and sunset to the blue light at midday. We share these involuntary responses with many creatures, from fish to single-celled organisms. Their marked ‘preference’ to photosynthesize (and our ability to concentrate) when the ambient light is bright and warm is just one example of the power of light and colour to shape our experience of the world.

Here’s an analysis of the wavelengths of light falling at different times of the day.

But as we said earlier, the light falling on an object is only part of the equation – what about surface and texture?

Two paint finishes show how the same colour can appear very differently.

In simple terms, there are four key dimensions to surface: reflectance (or shine’), transmission (or ‘transparency’), scattering (or ‘roughness’) and absorption.

We are incredibly good at reading this combination of colour and texture to ‘feel’ objects in the world - in fact, those two neural pathways are intimately connected. The ability to interpret those subtle visual cues are, oddly, more important than ever in this world of social isolation where we rely so heavily on the screen for our experience of the world.

The next level of processing is the ‘meaning’ or functional relevance of those signals - is this a ‘leaf’ and is it fresh and good to eat? Psychologists have shown that giving students a seat number written in red before their exam instead of a black one will reduce their grade by an average of 20%, placebo pills in warmer colours are more effective than those in cool colours, teams wearing red kit consistently beat those donning blue, men find women more sexually attractive when they wear red. The list goes on. And brands are well aware of those primitive and profound responses to colours and use them all the time to shape our consumption habits - we’ll talk more about that in the next webinar.

But those functional meanings seem to have given rise to an almost universal set of cultural meanings. For example, the colour black is broadly associated with shadows, death and evil, the colour red associated with passion, the colour blue with calm. It’s interesting to note that most of us experience some level of cross-over between those sensory modalities - a colour conjures up a sound, a taste, a shape or a movement. The celebrated Bouba Kiki experiment is a great example – people tend to assign a ‘soft’ word (bouba) and a ‘gentle’ colour (e.g. blue) to the shape on the left.

For some people with synaesthesia. that extends to a vivid and consistent integration of colour with other dimensions of experience.

The final level of processing is language - the names we give those colours. There are five universal colour categories - black, white, red, yellow and ‘blue/green’ or ‘grue’. Newton gave us the seven colours of the rainbow, while some cultures have no words for colours as we know them at all, simply qualities of objects such as different types of snow.

Women tend to have a wider vocabulary for colour words - and it turns out that the more names we have for colours, the more colours we are able to see. The names we use for colours also affects our experience of an object - a paint colour with a name that evokes taste, scent or other modality, e.g. ‘cappuccino’ is perceived as being of higher value. That light touch at work again.

So - in summary.

  • Colour is an ancient, universal and yet uniquely personal experience that shapes every aspect of our health and happiness - from our view of the planets to the beating of our hearts and the brands we buy.

  • This complex and dynamic experience arises from the play of light on surface and texture. As we are forced to spend more time indoors, each of us has the power and the responsibility to harness the power of light, colour and surface for good and for everyone.

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