This essay will explore how humans perceive, process, and comprehend colour information from the external world through studies and theories of mind and visual processing. Looking into the methods of both biological and cognitive aspects towards vision and colour. It will also examine and critique how perception can be influenced and misconstrued by elements such as the environment, culture and medical conditions.  
The traditional view of what makes colour unique among our visual perception was first articulated by Aristotle, who believed that colours are the proper objects of vision. He claimed that "colours grounded all aspects of visual perception and that the perception of colour was so direct the colours themselves enter the perceiver."   
Understanding how we perceive colour is vital to understanding how the eye allows us to detect it. Light enters the eye and is focused onto the retina by the lens. The light stimulates receptor cells on the retina, allowing us to detect them. These retinal receptors are called rods and cones. The rods detect grayscale and are used in our peripheral vision. Three types of colour-sensitive cone cells are pigmented to filter the wavelengths of light that hit them. (Akins et al., 2014) 
Human perception of light is a tiny fraction of the spectrum of electromagnetic radiation that can span from radio waves to gamma waves. The amplitude determines the intensity and brightness of the colour, while the wavelengths and frequency determine the hue. The short wavelength has a high frequency that displays blueish colours. The medium focuses on the green shades. The long wavelengths have low frequency, which shows reddish hues and the greater the amplitude, the brighter the colour. So, for example, to see a specific shade like lime green, the medium and long wavelengths get equal stimulation, whereas the small or blue cones get negligible stimulation. This unique ratio then allows the brain to interpret this colour as yellow-green. Although these cones can also see fine detail and colour, the fovea, cones can only function in well-lit conditions. This also means we can't see colour unless the cone cells are stimulated in different ratios. (Alfano et al., 2016) 
 
The Young-Helmholtz trichromatic theory suggested that the retina contains three specific colour receptor cones that register Red, Green and Blue (RGB). The three secondary colours in between RGB are yellow, cyan and magenta. These primary colours can create any colour in the correct ratios unless you are colourblind, a genetic defect and the majority affected are male. Many forms of colour deficiency are based around dichromacy, in which one cone is missing. Deuteranopia, green cones are missing. In protanopia, red cones are missing, and in tritanopia, the blue cones are missing (Millington, 1942).
Retinitis Pigmentosa (RP) is an inherited rare disorder that affects 18-23% of Japanese people and affects approximately 1 in 4,000 people worldwide. It can be X-linked as the mothers carry the mutated gene in one of their X chromosomes, giving it a 50% chance of passing it on to their son, and there is also a 50% of having a daughter who is a carrier. These genes are vital as they initiate specific protein production needed in the cells within the retina called photoreceptors. These photoreceptors are crucial as they begin the process of seeing by absorbing and converting light into electrical signals, which are the rods and cones (Collin et al., 2020; Davson, 1962). 
 
Opponent process theory suggests that we perceive colour through processes that clash, illustrating that some receptor cells can be potentially stimulated by green but inhibited by red, while others do the opposite, these combinations allow us to register colours. Hering (1878) explained that negative afterimages are the illusory perception of the complementary colour to the one that has just been fixated. So, for example, when you look at an image and then look at a white space, it is transferred to that space. In the 1950s, the research found that single-cell recordings found opponent neurons in the retina, which respond excitatory manner to one end of the spectrum but then in an inhibitory form in the other (Castelo-Branco et al., 2002; Rey et al., 2014). 
Wilhelm Wundt controversially created the first modern scientific concept of emotion and demonstrated that emotions were essential to rational thought. Wundt emphasised that vision was assembled in the brain from perceiving two distinctly different images. In contrast to A.W.Volkmann, who claimed that one eye's image was suppressed. Wundt then contended how vital both images were for depth perception: the ability to see objects in the three dimensions. However, images that strike the retina are two-dimensional. Using both binocular and monocular visual cues, depth cues such as retinal disparity depend on the images of both eyes. However, as these images only deviate slightly, retinal disparity does not aid in judging far-off distances. Monocular cues then help determine the distance of an object alongside relative size, height, linear perspective, texture, gradient and interposition. Motion perception infers the speed and direction of a moving object as the brain bases movement on the presumption that shrinking objects are moving away and enlarging objects are moving towards us. This then leads to perceptual constancy that continues the recognition of an object regardless of its distancing, viewing angle, motion or illumination. Instead, it is how you physically and psychologically understand the world and your place in it, as the sensory organs take in the raw data, which then become dissembled into small pieces of information. Then reassemble in the brain to form your model of the world resulting in the brain constructing perceptions. This is due to the top-down way our brains organise and interpret that knowledge and put it into context. This can result in bias from various areas such as emotions, surroundings, expectations, and cultural norms. Our perception is the process that allows us to make meaning out of our senses and experience the world around us, enabling us to make life understandable and realising that what we see may not be what we get, such as illusions. Illusions prove that the brain creates perception, and the eyes feed raw data, which is crucial. 
Opponent responding can be created by three types of receptors. Each theory describes physiological mechanisms in the visual systems. Such as trichromatic clarify the reactions of the cones in the retina. The opponent-process theory explains neural response for cells connected to the cones further in the brain. There cortical cells in both V1 and V4 either respond to some wavelengths or have opponent responses. These cells usually react to orientations forms, and cortical cells that respond to colours potentially react to white colour.  
Expectations are just one of the factors in your perceptual set, which are the psychological factors that determine how you perceive your environment. Context and culture are integral to the perceptual set, and emotions and motivations influence perception. (Coltheart, 2016) 
Form perception, which is the figure-ground relationship, is the organisation of the visual field into objects, the figure, and that stand out from their surroundings, the ground. Our minds can understand these amalgamations of stimuli by following grouping rules, such as organising the stimuli by proximity, continuity or closure. Continuity specifically as we tend to perceive smooth continuous patterns rather than discontinuous ones and closure in filling in gaps to create whole objects meaning that form perception is crucial in making sense of the world. However, what we see is the domain of the mind, not the eye (Eysenck & Keane, 2015) 
 
Previous neuroimaging research suggested that surface properties such as texture and colour are handled close to the collateral sulcus. However, a study implemented by Cavina-Pratesi et al. (2010) found a double dissociation between medial and lateral occipitotemporal cortices in processing surface versus geometric properties. Furthermore, it shows that an intermediate level visual processing sits midway of level processing. Specifically, how green areas selectively responded to colour, red to shape, blue to texture, and yellow spots responded to all three features.  
 
The visual functional specialisation theory depicts how different cortical areas in the brain are specialised for processing different visual attributes and functions. Such the V areas in the occipital lobe deal with specific visual regions. V1 and V2 are at the forefront as they deal with the early stages and initial processing of items. The cells in V3 and V3a respond to form, especially shape. The V4 reacts to colour and scene to line orientation, and the V5 and MT process visual motion (Tong, 2003). 
 
Zeki (2020) explored the multiplexing perennial binding problem, which is how form, motion, and colour can unify to visually provide a comprehensive image of the world. There are several processes in the brain, such as the Fusiform Gyrus (FFG) and all the V areas. If the binding problem is a problem, there needs to be a way to synchronise all this information to see what we see. Because of all these components, the data has to go to the correct ones for processing, such as the colour centre, so our brain can produce the experience of colour, deciding what wavelength or hue to create a specific colour. The information branched could potentially be sent to see for motion and even facial recognition. Amongst all the neurons in the rain that branch off, it is hard to imagine how the brain keeps track of it (Wolfe & Cave, 1999). 
Zeke (2020) illustrated how psychophysical experiments were invaluable in understanding how the brain "binds" colour to motion. For example, the study he conducted was on a screen where participants would be asked whether the squares were green or red depending on direction. So, for example, if the direction was going down, the squares would be turn green.  
Another example of the binding problem is a condition called Balint's syndrome, which processes different modules as the brain misattributes and upon processing between the various modules. For example, when unified, the brain misattributes the colour information to the wrong object. This can be a danger as the object could be a moving vehicle by a stationary object. Still, because of the swap, it could also flip the colours from bright to dark, so potentially not seeing the vehicle moving towards them but instead a stationary object such as a lampost. There is also the main issue which is synchronicity. DiLollo (2020) later disagreed with Von der Malsburg (1981), expressing that binding is an ill-posed problem as modules can code jointly for multiple functions. Furthermore, the neurons can respond with more than one property, even though the neurons work in a one-way system, the electrochemical messages can be looped back. Even though Wolfe indicated that DiLollo had misunderstood the problem and incorrectly mapped the issue on the brain, he does agree it was an ill-posed problem and that object perception was a fundamental problem (Wolfe & Cave, 1999). 
 
Colour Rendering Index (CRI) describes how well artificial light reproduces the colour of the objects around us. For example, incandescent lights, which are blackbody radiators, have a perfect CRI, just like the sun. However, light sources that are not incandescent do not emit light as a perfectly uniform spectrum. However, if an object were lit solely by a monochromatic light source such as a red LED, it would fundamentally shatter the colour vision as it relies on the mixing of colours to determine what we are seeing (Staff, 2018). 
 
Evolutionary psychologists such as Steven Pinker (2005) have argued that the makeup of our brains determines our thoughts and actions and that they are like other inherited characteristics subject to the laws of natural selection. Jerry Fodor argued against Pinker, contending that the Turing machines cannot duplicate humans' performance. Still, Pinker countered this, explaining how he had misinterpreted and believed that the mind has the architecture of a Turing machine.  
 
Shepherd put forward that the brain processes sensory data to make decisions and assumptions on an internal world model. We can visualise objects in three dimensions and the experiment he used to prove this. Subjects attempted to establish whether two tables, drawn from separate angles, were identical and showed we could perform what Shepherd coined "mental rotation". This led to further research introducing revolutionary techniques for identifying the hidden structures of mental representations for processes (Shepherd, 2016). 
 
To conclude, the dual-processing theory is vital in processing colour information and vision established on two types of processing: bottom-up processing, which is data-driven. First, the raw data is taken in, then the features are put into focus, followed by the concept, which is when the brain draws in experience and meaning then decides, for example, seeing the components of a chair separately then realising it is a chair. The strength of this process is that it is founded on reality however, the limitation is that this is a lengthy method. The other is top-down processing which is expectation or knowledge-driven. The first stage is determining how the world is. The concept, which can influence recognition, then passes onto features affecting how data is perceived, affecting data receptors. This is because more neurons from the cortex are feeding downwards and towards the data with these messages. The strength of this process is that it is quicker, but it can also mean what you see is not correct such as witness statements can be seen as unreliable. 
Colour signals are vital as they help categorise and recognise objects also facilitate the perpetual organisation of elements into objects. This is because white light contains all of the wavelengths of the spectrum, and when all wavelengths are reflected equally, that is when we see white (Collin et al., 2020).  
How we use vision and sound simultaneously can be seen as another way the brain binds all these stimulations and information together. For example, Mayer & Moreno (1998) conducted an experiment between-subjects design. These parameters were narration and screen text, and both groups then completed a memory recall test. The results found that the group could combine words and pictures easier when delivered auditorily rather than visually. 
The environment can also influence how we perceive colour and even respond to illusions. Pedersen and Wheeler (1983) found that through the Muller-Lyer arrow illusion, people who lived in roundhouses with no corners were less susceptible to this illusion than people who lived in rectangular houses. There are also factors such as pollution as western countries see the sun as yellow, but in India, the sun is seen as more red.