As a living, conscious human being I must struggle to make sense of the world. It often feels as if there is so much more than I understand and that I understand only a small part of what I see. Yet survival and the precise course of each of our lives often depends on getting this stuff right.
A simple description of the challenge that all human beings face concerns the correspondence between organism and environment. In purely physical terms the boundary between the two follows the contours of our skin and there is a significant difference between the inside and outside until our lives come to an end.
If this perspective is maintained, the relationship between the living organism on the inside and the living environment on the outside is mediated by the epidermis, where blood and tissue interface with air. Nerves, embedded in every square inch of the surface of our skin, enable tiny changes in the immediate environment to be sensed. Other nerves within the nose and mouth collect their own sensory impressions. Add to this a proprioceptive awareness of our own movements and sense of balance, then, taken together, these sensations provide an essential avenue to assembling our understanding of the world.
Obviously, there are two other organs evident on the surface of our bodies that vastly expand our relationship with the world outside. They are, of course, hearing and vision. Of these two it is vision that provides the principal focus of everything that follows.
To add vision to the emerging equation outlined so far involves the eyes, the optic nerve and brain. All three can be counted as the component parts of a single organ embedded safely within the skull, but with the eyes mounted as high up and as far forward as possible from where they can provide the best high-resolution imaging service possible.
It may already be clear that this somewhat simplistic idea of human existence as a transactional relationship grounded in being-in and being-of the world in a purely physical sense is too limited. Our lives stretch beyond the reach of our organs. Our immediate circumstances run out into global computer networks, allowing us to engage in instantaneous transactions worldwide. Connect the human mind to a microscope and we see, for example, into the infinitesimally small world of neurons and synapses that power vision and conscious perception. Do an internet search, or access libraries online, and we unlock petabytes of knowledge of ourselves and the world accumulated over centuries.
In a very real sense, it is visual perception that provides the key to the breadth of perspectives we have on our very human condition, brings our experience of the world into sharp relief and fills every corner of it with colour?
As a point of departure, consider the following three points:
- Colour is always there whether we are aware and pay attention to it or not. Colour is what human beings see in the presence of light.
- Colour is an artefact of human vision, something that only exists for living things like ourselves.
- Seeing is a sensation that makes us aware of light and takes the form of colour. If human beings and related species were all to disappear overnight, the world would still be full of light but there would be no colour.
Visual perception is the human ability to see and interpret the surrounding environment because of the sensitivity of the eyes to wavelengths of light corresponding to all the colours we see between red and violet.
Light striking the retina at the back of the eyes initiates a cascade of chemical processes, and then electrical impulses, that are sent to visual centres of the brain through the fibres of the optic nerve.
- Visual perception is associated with eyesight but also usually refers to the brain’s ability to make sense of what our eyes see.
- The human eye and so human vision are tuned to the visible part of the electromagnetic spectrum.
- There are no properties of electromagnetic radiation that distinguish visible light from radiation in the other parts of the electromagnetic spectrum.
- Colour is not a property of light, but a feature of the visual perception of an observer. So colour is what human beings see in the presence of light.
- Objects appear to be different colours to an observer depending on the wavelengths and intensity of light striking the retina.
Attributes of visual perception are the innate abilities and the skills we develop over the course of a lifetime that enable us to make sense of what we see. They are evident in the diverse properties of the world we see around us.
Innate attributes of visual perception associated with the response of the human eye and brain to light include:
- Colour perception: The ability to see colour in the presence of light including all the greys between black and white.
- Visual attention: The ability to focus on important visual information and filter out unimportant background information.
- Sensory processing: Accurate registration, interpretation and response through the coordination of visual information with other forms of sensory stimulation.
- Visual discrimination: The ability to recognise differences or similarities in objects based on size, colour, shape, etc.
- Spatial relationships: The ability to understand the relationships of objects, particularly their distance, direction of movement and position relative to an observer.
- Figure-ground: The ability to locate something against a busy background.
- Form constancy: The ability to know that a form or shape is the same, even if it becomes larger or smaller, or its orientation changes.
- Visual closure: The ability to recognise a form or object when part of it is hidden or missing.
- Visual memory: The ability to recall visual traits of a form or object.
- Visual sequential memory: The ability to recall a sequence of objects in the correct order.
In terms of human experience, colour vision is the ability to distinguish objects based on the wavelengths and intensities of light they absorb, emit, reflect or transmit. The human eye and brain together translate light into colour.
- Colour vision allows a human observer to distinguish objects by their colour.
- Colours can be measured and quantified, but an observer’s perception of colour is first and foremost a subjective experience whereby the eye and brain respond to the stimuli that are produced when incoming light reacts with chemicals inside the photosensitive rod and cone cells in the eye.
- In normal conditions, light is rarely of a single wavelength, so an observer will be exposed to a range of wavelengths in one area of the spectrum or a mixture of wavelengths from different areas of the spectrum.
- In everyday life, colour vision includes chromatic and achromatic content. This means that an observer can distinguish between stimuli that appear coloured and others that appear to be without colour and so appear black, grey or white.
- Different people often see the same illuminated object or light source in different ways.
The perceived colour of an object, surface or area within the field of vision is an attribute of visual perception. First and foremost, perceived colour refers to what an observer sees in any given situation and so is a subjective experience.
- It is the human ability to perceive and distinguish between colours that provides an important basis for the way that we sense and make sense of the world.
- A distinction can be made between the physical properties of things in the world around us and how they appear to a human observer.
- When talking about perceived colour, a distinction can be made between:
- The properties of light.
- The properties of objects.
- What an observer perceives as a result of the attributes of visual perception.
- Perceived colour can be described by chromatic colour names such as pink, orange, brown, green, blue, purple, etc., or by achromatic colour names such as black, grey or white etc. Colour names can be qualified by adjectives such as dark, dim, light, bright etc.
- Colour perception consists of any combination of chromatic and achromatic content.
- Perceived colour depends on the spectral distribution of a colour stimulus and so the range and mixture of wavelengths and intensities of light that enter the eye.
- Colour perception tends to provide visual information that is most important to an observer rather than information that is always objectively accurate.
- Perceived colour depends on factors such as the size, shape and structure of all the objects in view, the composition and texture of their surfaces, their position and orientation in relation to one another, their location within the field of view of an observer and the direction of incident light.
- Colour perception can be affected by the state of adaptation of an observer’s visual system. An example of this is when the photosensitive cells embedded in the retina become fatigued from long exposure to strong colour and then produce an afterimage when we look away.
- Perceived colour is strongly influenced by factors such as an observer’s expectations, priorities, current activities, recollections and previous experience.
- Perceived colour is defined in the International Lighting Vocabulary of the CIE (The International Commission on Illumination) as a characteristic of visual perception that can be described by attributes of hue, brightness (or lightness) and colourfulness (saturation or chroma) (CIE, 2011, 17-198).
A starting point in understanding the connection between visual perception and sense-making is that as light enters our eyes it does not have any properties that allow it to carry information about the world we so easily recognise around us.
So far as physical processes within the eyes are concerned, everything an observer sees and understands about the world before them must be constructed from chemical and then electrical processes. These signals are initially triggered in the layer of photosensitive rod and cones cells embedded in the retina and then by further processing that takes place in other types of retinal neurons such as ganglion and bipolar cells.
This perspective on the role of the eyes in visual perception and sense-making might suggest that the process begins as light strikes the retina and ends with a conscious perception. But other models suggest that chemical and electrical processes resulting from light stimulating the eyes and neurological activity stimulated by the brain occur simultaneously and that conscious perceptions are as much to do with brain state as they are to do with raw information gathered by the eyes.
Let’s look at this more closely!
It can be argued that our everyday experience of making sense of what we see involves a kind of naïve realism. When we look around we simply perceive the world as being out there, though our attention may swing inward at a moment’s notice if we feel pain or have a disturbing thought.
Most people are familiar with the idea that colours do not have an external objective existence. This understanding has a grounding in physics. Light is energy of different wavelengths and our eyes have receptors that respond to one small band of those wavelengths within the electromagnetic spectrum. Biology and related sciences have in turn revealed the fact that our eyes have light receptors that generate the experience of colour.
There is no red out there in the world. What we call red is our visual system’s interpretation of what is out there. My brain constructs the experience of red from the data provided by my eyes. Despite all this, when I see a car, the fact that it is red is an indisputably accurate description of my observation. Somehow redness and car appear as one.
Neuroscience is currently trying to explain how this happens. What we do know is that our visual system favours rapid interpretation and fast reaction times and works on the basis that there is nothing to be gained from the brain revealing its inner workings in the course of everyday experience. To the contrary, it specialises in providing us with just the information we need and in precisely the form that we need it. We receive no information about how our eyes and brain gather or process information.
A physical description of the way that visual perception and sense-making begin is that light flows into our eyes from the world. Photons bounce off things in front of us first, enter our eyes through the pupil and undergo various forms of visual processing. Perhaps it starts with points of interest, joining dots into lines, lines into shapes, shapes into objects and then placing objects into scenes complete with movement.
An anatomical view of the brain shows that the connections going towards the eye from the brain control things like eye movement, vergence of the two eyes, focus and blinking but that there are vastly greater numbers of connections going in the other direction towards the brain.
It would be mistaken to think of our eyes as a separate organ. Eyes are literally extensions of the brain, mounted remotely from the visual centres, but directly connected by a series of neurons attached to the retina at one end and the visual cortex at the other.
Eye through to visual cortex
From this perspective, the visual system relies on light being focused into an image on the back of the eye and its translation into meaningful nerve signals by intricate and complex processing circuitry. The signals are then dispatched along the optic nerve to the visual cortex and other related areas of the brain.
Each of these perspectives suggests that vision is tuned to different aspects of the world around us and that the perception of colour, shape, depth, stereo vision and movement all help us to pick out details and outlines of shapes whilst also integrating local and global features of objects into a comprehensive view of the world.
Seen in these terms, the visual system is a kind of bottom-up process that relays information from the eyes to other departments that get excited by this input.
But what about a top-down perspective? We can also think of perception and sense-making as depending not just on information derived from light entering our eyes but also that it results from the complex interplay of processes that originate in our brains.
Perception is not just a question of what we see but the fact that the brain has its own ideas about what is going on and this includes our self-perceptions. In this sense, different kinds of perception are like different kinds of hypothesising.
The implications are that the activities of the visual system are as much about mental processes at higher levels as about raw visual information coming up the optic nerve. This comes down to the idea that the visual system is trying to imagine what is out there. Depending on circumstances, out there might mean inside my elbow, inside my shoe or inside my computer!
Top and bottom process
A top-down view involves signals carrying predictions about what is happening in the world being evaluated at the top end of the visual process whilst the brain also tries to make sense of what is causing sensory data at the bottom end. It is a meeting of many types of processing out of which visual experience is constructed. What we see is the result of the visual system’s best guess about what is causing sensory data and its predictions about what will happen next.
These ideas get us away from an overly physiological and hierarchical ordering of the visual system and open ways of thinking grounded in our bodies as they actively live, learn and act in the world.
It is clear, for example, that during childhood we begin to become familiar with our surroundings, and as that process develops we become more efficient at making sense of it. As time goes on, it involves less effort to recognise features and so the more quickly we apply that familiarity next time around.
How we see objects and extract meaning from a scene may depend on what we are doing with the things before us and whether we are carrying out a familiar task. In another case, faced with something unfamiliar, we may scan an array of barely recognisable objects and ask ourselves questions about what things are and whether they relate to the task at hand. Riding a bicycle might provide a good example in the first case whilst lifting the bonnet of a car for the first time to check the oil could apply in the second.
If we take all this one step further, then we imagine the world we see. Imagination, anticipation, inference and hallucination are all part and parcel of trying to see things. We couldn’t do the act of seeing without imagining. And of course, usually we get it right, but sometimes we do get it wrong.
Matching mental assumptions about the world with the information simultaneously processed by the retina is clearly something that has evolved over millions of years. Given the benefits of trial and error over that time, we can be reasonably confident that the endurance of our species indicates that the match between the two is often spot on.
It is particularly comforting to see how quickly mistakes like seeing cats that turn out to be rocks are rectified. At the other end of the scale when paranoia, delusions, fear, conspiracy theories or over-active imaginations prevail, it reflects the degree to which the match can slip out of kilter even for a reasonably well-adjusted personality.
We constantly check our immediate needs, our hopes and imaginations against information gathered by the retina. But some people clearly have problems accurately perceiving the world around them. This does not necessarily involve mistaking objects but can take place as moods and emotions intertwine with our perceived view of the world.
Take for example the effect of something as simple as a pain-killer for a headache, a hot drink after a tiresome day, or a substantial meal when physically overtired. The rhythms and shifts that affect every organ in our body impact on how we see the world.
Then there are situations where we close our eyes whilst listening to music or begin an imaginative activity. By suppressing the generation of information from the eyes we can stimulate a creative process still packed with images that are quite apart from the ordinary features of everyday affairs.
These perspectives fit with contemporary descriptions of the visual system that reject a simple ordering of different components, processing steps and the idea of narrow areas of specialisation within and around the visual cortex. They suggest instead the idea of myriads of links and relays between neurons interconnecting the diverse dimensions of what we experience directly as conscious perceptions. This approach recognises the brain’s role as being fluid and adaptable to specific circumstances with a dynamic and synergistic role in constructing our visual experience as a perceptual whole. This, in turn, is only a part of what it means to be a conscious living member of humanity embedded in ecosystems which have a 3.8-billion-year history.
Who exactly is the person that seemingly lives behind my eyes? Who is it that lives behind any other pairs of eyes I look at during the day? I can talk about myself. I can say that behind each pair of eyes is a separate self. But what is a self?
One point of view within contemporary philosophy suggests that there is always someone having the experience – someone consciously experiencing themselves as directed toward the world, as a self in the act of attending, knowing, desiring, willing, and acting. This view suggests that we have an integrated inner-image of ourselves that is firmly anchored in our feelings and bodily sensations providing for the experience of a point of view. This approach recognises however that there is no little person running things inside our head. (Metzinger, 2010, pp. 7-8)
This problem of identifying a self was recognised by another philosopher, David Hume, more than two hundred and fifty years earlier in his book A Treatise of Human Nature:
“When I enter most intimately into what I call myself, I always stumble on some particular perception or other, of heat or cold, light or shade, love or hatred, pain or pleasure. I never catch myself at any time without a perception, and never can observe anything but the perception”. (Hume, 2015, p. 254)
The idea of self, along with that of being a subject who can, for example, see objects, is therefore not quite straightforward. What do I mean when I say that I am just being myself. There is obviously more to it than the fact that I can only pretend to be someone else!