The History of Colour Vision Science

Early philosophers and scientists held very different views regarding vision and colour perception than those now accepted in contemporary vision science. In this component of the Bases of Colour Vision, we will explore some of those views.

Views of the Early Greek Philosophers
Reflecting the zeitgeist of the age, the early Greek philosophers of Hellenic times escaped the use of experiments to explain the experience of colour. This non-empirical speculative approach is reflected in the following statement by Plato (429-347 BCE) regarding colour vision.

"The law of proportion according to which the several colours are formed, even if a man knew he would be foolish in telling, for he could not give any necessary reason, nor indeed any tolerable or probable explanation of them. "

- Plato, Timaeus 68

Plato's statement reflects one of the most enduring problems in the history of colour vision science - the dependence on assumption over observation.

In the fifth century BCE, Empedocles (493-433 BCE) wrote that the eye functioned like a lantern, that light from the eye shining outwards would interact with the "outer rays" and thereby allow objects to be seen. This concept was later refined by Plato in his emanation theory.

Aristotle (384-322 BCE), Plato's devoted pupil, propagated a different notion of colour vision. He thought that colour was based on the interaction of stimulus brightness and ambient light level. He based this view on the perception that the colour of a sunset changed as darkness set in.

The Middle Ages (5th c. - 15th c. AD)
Ravaged by plagues, poverty, and religious wars, Europe did little to advance the cause of science or our understanding of colour vision during the Middle Ages. Many thought God would not approve of such tinkering with His creation. 

The Arab scholar Alhazen (965-1069 CE) proposed a camera obscura model for the transmission of light in the eye, but did not speculate on the basis of colour vision.

The Foundations of the Trichromatic Theory
The seventeenth century marked the beginning of the Enlightenment in Europe, an era characterized by the emergence of self-declared "scientists." Pre-eminent among them was the universal genius, Sir Isaac Newton (1642-1727).

Newton escaped the confusion between the proximal and distal stimulus by experimentation. He is famous for his experimental demonstration that a prism could refract a narrow beam of sunlight into all the colours of the rainbow. He also showed that the colours that compose white light could not be further subdivided, but they could be recombined to form white light. His conclusion was that colour is not the product of the external objects we see, but is a property of the eye itself. This provided the foundation for modern theories of colour vision.

Despite his interests and contributions to colour vision, Newton did not concern himself with proving his theories on colour perception.

The scientific notion that colour vision is explained by the action and interaction of three different "particles" (cf. Newton, Palmer, Young, Helmholtz) was not actually proven until the twentieth century when modern scientific techniques permitted the discovery of three different cone photopigments. Early attempts at "trivariance theory" proper was only one among "many-variance" theories.

George Palmer (ca. 1786) was one of the first to put forward the notion that colour vision is based on the "maximal sensitivity" of retinal "particles." Palmer is not usually given deserved recognition for this original idea; credit for this important idea is often erroneously given to Thomas Young.

Thomas Young (1773-1829) argued that there was a limited rather than infinite number of different retinal "particles" at every point on the retina to respond to light. He suggested that there might be three such particles only, a view later validated by science. His key contribution to colour vision science may have been to restate Palmer's concept of spectral sensitivity.

Hermann von Helmholtz (1821-1894) championed Young's idea that retinal particles varied in the light to which they were "maximally sensitive." As a result, the trichromatic theory of colour vision also came to be known as Young-Helmholtz Theory. Influenced by his colour mixing experiments, however, Helmholtz could not accept the notion that there could be fewer than five colour primaries. Thus, he failed to accept the three retinal primaries proposed by Young.

A contemporary of Helmholtz, physicist James Clerk Maxwell (1831-1879), suggested that any physically pure primary is bound to be subjectively complex due to the complexity of the underlying processes. He held that the eye creates colour, and the observation of colour taints the experiment itself. In this Maxwell broke free of the last remnants of naive realism. His was the last major contribution of the nineteenth century to spectral sensitivity.

Ewald Hering and the Opponent Process Theory
Ewald Hering (1834-1918) observed that the "trichromatic theory" could not explain the phenomenon of afterimages, negative-coloured images seen after extended viewing of a coloured object (e.g., red after green, or yellow after blue). Hering based his work on the subjective appearance of colours, and wondered why certain colours could never be seen or even described, such as bluish-yellow or reddish-green.

Hering proposed that the visual system generated signals in opposing pairs (i.e., yellow-blue, red-green, white-black). However, it was not until much later in the twentieth century that neural experiments proved him correct. At the time his theory was seen by many to compete with the trichromatic theory. Hering himself held that both theories could be equally valid. We now know that he was correct - the two theories simply reflect processes at different levels of visual processing.