COLOURS’ VISION

The two main theories of colour vision that emerged in the nineteenth century offered at the time alternative ideas on the nature of biological mechanisms. Physiological studies have then clarified the complementarity of the two theories.

During the night with little light we can perceive the shapes only as grey forms, then the sun of the day arrives and a world in colours explodes.
The ease in recognizing them, like their beauty, depends on light.

Plato first approaches a theory about colours perception based on energy, mediating objective physical elements and subjective transcendental elements.

Plato stands between the “put-in” and “get-out” schools and the Aristotelian doctrines.

In the first case, the introduction into the eye of a physical and objective picture from the material forms is foreseen, even in the absence of light (Pythagoras, Empedocles). In the second case, the eye emanates something that comes from the soul, a sensory force that can perceive subjectively to real color belonging to the body.

For Aristotle, the vision happens for the presence of light, power in the ether, a medium, without energetic or corpuscular interaction.

Plato considers the eye as the place where the inside energy blends with the external energy: “pure flame” within us meets a similar “daytime flame” that is outside of us. The colors, the vision and the perception of the materials arise by the fusion of these two flows.

Plato sense by intuition a principle of opposition that regulates the process of perceiving and synthesis of colors.

“Wherefore, we ought to term white that which dilates the visual ray, and the opposite of this is black.”

The expansion of the visual fire causes the sensation of white, whereas its contraction causes the sensation of black. Black and white are originated by the interaction among exterior fire and material bodies, they are two extreme sensations that allow the perception of flashing flames derived from visual fire.

These flashing flames are named brilliant (lampron) and glittering, in the middle between them there is a kind of intermediate flame, perceived as the red (eruthron), so on for subsequent combinations, we get all the colours.

After about seven centuries from Plato, between 200 and 400 AD, Plotinus is the leading exponent of the Neoplatonic school, confirming the energetic nature for the phenomenon of synthesis and perception of color, Plato’s fire takes the name of the light, and its double existence both in the outer and inner world.

“The beauty of colour is also the outcome of a unification: it derives from shape, from the conquest of the darkness inherent in Matter by the pouring-in of light, the unembodied, which is a Rational-Principle and an Ideal-Form.”
[Plotinus, Enneads]

For the light of the bodies and the inner light Plotinus uses the same word (fos), which unfortunately mutate into two words in Latin, respectively lumens and lux in all disciplines (the scientific, the philosophical and the theological one), in the medieval scholastic literature, from the mid-twelfth century up to Descartes.

However, the Greek works reach the Islamic world and they are translated into Syriac and Arabic, and Ibn al-Haytham, called Alhazen by the Europeans, raises the bar and develops new knowledge on colour vision.

He senses by intuition the energetic nature of light, which he defines as a sort of force, energy emitted by the Sun, a radiation that is so strong that it causes the production of visual information coming from objects. Colour is the effect of secondary radiation, emitted by excited objects by a primary agent, such as sunlight.

For Ibn al-Haytham colour and light are always together, they are fused, mixed, inseparable. Colour does not manifest itself without light and light always has a colour.

Ibn al-Haytham goes beyond the obstacle, and perhaps first, experiments with the chromatic dispersion of light with spheres full of water. In this way, he sees that the rays of light that cross the sphere are separated according to measurable angles and he realizes that each ray produces a certain colour with a univocal correspondence.

After seven centuries of the Neoplatonic school, the dispersion of light is born, which anticipates the experiments of refraction by Snellius and Descartes (1637), the wave-theory of light by Huygens (1678), the colour wheel by Newton (1704): knowledges that are developed after another seven centuries from the experiments of Ibn al-Haytham.

Newton, driven by a new wind of experimental science, studies on the separation of colours of light (rainbow) through a transparent prism. He focuses on color physics:

“All the Colours in the Universe which are made by Light, and depend not on the Power of Imagination, are either the Colours of homogeneal Lights, or compounded of these, and that either accurately or very nearly, according to the Rule of the foregoing Problem.”
Isaac Newton.

He elaborates the principle of synthesis of intermediate colours within the colour spectrum (rainbow): by adding green light to red light, a yellow light is obtained. It is also possible to mix the two extreme primary colours of the rainbow, the red with the violet, which gives rise to violet- colours whose colour is not similar to that of any spectral colour but which appears visually intermediate between red and blue, the magenta.

The colour wheel is born, and first consider red and purple as two “contiguous” colours.

Dopo un secolo arriva un grande passo per capire il legame tra luce e visione oculare da parte di un medico Inglese, Thomas Young. All’età di 28 anni nel 1801, presenta alla Royal Society le sue teorie sulla fisiologia del sistema visivo, e sul principio tricromatico RGB che si genera nell’occhio, intuendo i fenomeni che avvengono nella retina.

After a century, a great step comes to understand the link between light and eye vision by an English doctor, Thomas Young. At the age of 28 in 1801, he exposes to the Royal Society his theories on the physiology of the visual system, and on the RGB trichromatic principle which occurs in the eye, sensing by intuition the phenomena that occur in the retina.

From then on, driven by positivism and the resulting technological and industrial revolutions, a vast quantity of studies on light physics, colorimetry and color physiology are generated: Hermann Grassmann (1809-1877) dictates the axioms trichromatic theory, Helmholtz (1821-1894) tests it experimentally, Maxwell (1831-1879) quantitatively build the mathematical model that describes the electromagnetic wave nature of light and the principles of three-color theory, Einstein in (1905) introduces the notion of quantum of energy and the photoelectric effect, which earned him the Nobel prize, and reopens the centuries-old debate on the nature of light, and limits the validity field of Maxwel’s equations.

In the same period Hering (1834-1918) develops the theory of chromatic opposition, which at the time seemed to be in clear opposition to the trichromatic theory.
This theory hypothesizes that in the eye there are three bipolar mechanisms, which generate signals in pairs of opposite colours: red-green, blue-yellow, white-black.

The two main theories of colour vision that emerged in the nineteenth century offered at the time alternative ideas on the nature of biological mechanisms.  Physiological studies have then clarified the complementarity of the two theories. The trichromatic theory best describes the first phase of physiological sensation, in which the electromagnetic light signal is separated into three main tonal lights. A principle of chromatic opposition is fundamental to understanding the second phase of the visual process. The stage for the interpretation and perception, which translates and encodes the signals coming from the photoreceptors through simultaneous and mutually exclusive opposition process.

Finally, in 1931 on the basis of the work of Wright and Guilt, the CIE International Commission on Illumination, creates the first color space, which allows to univocally encode with trichromatic coordinates (XYZ) the electromagnetic energy and the physiological sensation.

Several experimental observations, known as “hue cancellation” experiments by Jameson and Hurvich (1955-1957), allows to catapult forward and linking the XYZ colorimetric model and Hering’s opposing color theory, creating a large vein central investigation in the science of vision.

In 1976 the CIE transformed the three XYZ (RGB) coordinates into three Lab colour coordinates: L for black and white achromatic axis, and the chromatic plane with two axes: the first with red (+ a) in opposition to green (-a) and the other with yellow (+ b) opposite to blue (-b). This coding is still used in colorimetry to measure colours with artificial instruments today.

The XYZ code and the Lab code describe the same phenomenon, the first has a logic of input and the second is guided by a measurement logic of the output, which best fits a process of opposite signals collimation.

The transformation from three-dimensional space XYZ to a three-dimensional space Lab also occurs in our visual system, more precisely in the thalamus.

The trichromatic signal is generated in the cones in the ocular retina, classified S (high energy – Blue), M (medium energy-Green) and L (low energy – Red). The light leads to a hyperpolarization of the receptor cone, which switches from -40mV to -75mV, and emits electrical (amplitude modulation) and biochemical signals.

The receptor signal is subsequently processed in internal cells (on-off relay neurons, called bipolar, horizontal and amacrine cells), changing its logic (frequency modulation). The signal exits the retina through ganglion cells, and it continues along the optic nerve and reaches a region of the thalamus, called the lateral geniculate nucleus (LGN). LGN is a hub central station of visual information coming from the eye and destined for the primary visual cortex (striate cortex).

LGN ganglion cells are of two types: M (magnae or large) and P (parvae or small), the signals are divided into two channels. An achromatic channel for luminosity and movement starts from the M cells. The chromatic channel starts from the P cells. The two channels have an operating principle by opposition.

The positive value combines with the negative values and creating a grayscale signal of brightness. In the chromatic channel: the measured -L value matches in opposition with “calculated” values + M. The + L (calculated) value combines with the measured -M values. In this way the initial values S, L and M are transformed into code with Lab logic.

The code produced in the thalamus reaches the primary visual cortex (striate cortex) and from here on out the path is for now obscure, the future still reserves surprising discoveries.

The physical nature of the code is at stake. It is no longer just electromagnetic, but a new physical property is needed to describe colours significance and consciousness, our ability to perceive and understand through sensations.

Recent studies by Federico Faggin, Italian physicist and American Entrepreneur, are in this research field. He is today, in “his fourth life”, involved in the challenge launched by Plato.

Currently fMRI (functional magnetic resonance) technologies have enabled neuroscientists to map conscious states in the brain, however, despite the familiarity that consciousness has for each of us, it remains a great mystery to science.

“There is no known physical principle that can translate electrical activity in the brain or in a computer into sensations or feelings.”

Faggin proposed a new model of physics, which is based on the assumption that consciousness is an “irreducible” property of nature.

He introduces “the concept of consciousness units (CUs), the fundamental “components” of all that exists: space, time and the quantum fields of the fundamental particles.”

“Objective” and “subjective” must be two intertwined and inseparable aspects of an indivisible whole from the beginning. In other words, the nature of reality intrinsically has an inner and an outer aspect that are irreducible, co-emerging, and co-evolving. In this model, the inner aspect is the semantic reality of each self; the outer aspect is the informational or symbolic reality that gives rise to all the physical worlds. The evolution of the physical universe must therefore reflect in some way the semantic evolution of the selves, and vice versa – one reflects and supports the other.”  
Federico Faggin, May 2019.

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