Blog post 16 is dedicated to the human visual system - our mind's highest bandwidth connection with external reality. As an artist with a background in biology, vision is a recurrent theme in my drawings and sculptures, which often consider the strengths, weaknesses, origins and limits of the 'wet-ware' that underlies visuality, and facilitates the way we create and experience visual art. Our scientific understanding of vision is constantly evolving over time, and this is something I try to take in to account as an artist.
Figure 1. Ibn al-Haytham: Diagram of the human visual system. From a 1083 copy of his Kitāb al-Manāzir
in the Süleymaniye Library, Istanbul.
It's now over a thousand years since the Golden Age of Arabic Science, during which time Ibn al-Haytham published his magisterial 7 volume treatise on optics the ' Kitab al-Manazir ' (1015), from which the diagram in figure 1 is taken (1).
Translated into Latin in the 13th century as ' De Aspectibus ', and again in 1572 after the advent of the printing press, the ideas it contained would influence generations of European thinkers throughout the middle ages and on in to the Renaissance.
Al-Haytham's methodical attention to detail and insistence on evidence based reasoning meant that he's often referred to as not only the father of modern optics, but one of the World's first true proponents and practitioners of the scientific method.
Figure 1 is particularly interesting because of artistic restrictions on Muslims against depicting living or sentient beings, known as Aniconism. However Al-Haytham's use of the abstractive powers of the diagram meant that he was able to draw an elegantly stylised nose, the eyes and their lenses, and the optic nerves to the visual cortex at the back of the brain (shown here at the top of figure 1). Remarkably, he even included the chiasma or 'crossing point' of the optic nerves within the brain.
Al-Haytham's work on optics proposed a systematic solution to the problem of vision that combined experimental investigations in to the behavior of light with inventive geometrical proofs and constant forays into the psychology of visual perception. His insight that light is composed of particles for example, would later described by Newton and finally proven by Einstein in his work on the 'photoelectric effect' in 1905, for which he later won the 1921 Nobel prize for physics.
The treatise offered a coherent alternative to the Euclidean and Ptolemaic theories of visual emission, in which visual rays were believed to be emitted from the eye, curiously emphasized by the peculiar hands gestures in figure 2 below. This esoteric idea was first proposed by the 5th century Greek philosopher Empedocles, who claimed that vision was enabled by the goddess Aphrodite, who lit a divine fire within the human eye.
Johannes Kepler (b.1571) directly followed al-Haytham's formalism to its inevitable and logical conclusion in his mechanistic theory of the retinal image that was to replace its impressionistic predecessor. However even he struggled to accept what al-Haytham called the "monstrous" distortion of sensation that would be provoked by inversion of the image, and it remained for René Descartes (b.1596) to compile his own theory of vision, beautifully illustrated with diagrams and far closer to our current understanding. (figure 2).
Figure 2 above depicts Descartes theory of how physical impulses are transmitted in the form of rays from the arrow into the eye give rise to physical impulses through the optic nerves and then into the brain to the pineal gland, which he incorrectly believed served as the nexus between the immaterial mind (which he referred to as res-cogitans) and the physical body (res-entensa).
Figure 3: Descartes' blind man probing the environment with sticks. No confusion arises concerning the location of objects despite the fact that the sticks are crossed.
He goes on to point out that so long as there are systematic rules that link eye or body motions to changes in the retinal image, the brain will be able to construct a correct representation of space.
Cleverly, descartes uses the analogy of a blind man who is exploring his environment with the aid of a stick AD, held in his right hand and a stick, CB, held in his left hand (figure 3).
Even though the blind man may cross the sticks in front of him, just as the image is inverted on the retina, no confusion concerning the location of objects will result from this. (3)
Until only recently the idea of fully understanding the inner workings of the eye was considered a problem of such intractable complexity that it was often held as evidence of a supernatural engineer. Even Darwin himself appeared troubled at first, remarking in an often misquoted aside in Origin of the Species that the whole idea that something so flawless “could have been formed by natural selection, seems, I freely confess, absurd in the highest degree.”
However as with all complex biological features, the human visual system arose unimaginably slowly over hundreds of millions of years of clumsy trial and error, and on closer inspection we find numerous examples of evolutionary concession and compromise. As a result, the human eye and visual system is just good as it needs to be and no better, and systemic errors have to be accommodated for using sophisticated cognitive processing techniques (the blind spot is a good example of this).
For an excellent article covering this topic click here: The Poor Design of the Human Eye.
The last decade of brain research has revealed more about the human brain than all the years of prior research combined. The number of neurons devoted entirely to visual processing is now estimated to be in their hundreds of millions, taking up about 30% of the whole cortex, as compared with 8% for touch and only 3% for hearing. Each of the two optic nerves that carry signals from the retina to the brain consists of a million fibers, whereas each auditory nerve carries a mere 30,000.
two point source interference patterns), 2017, 97 x 92 cm, Ink, pencil and watercolour on paper
It's probably worth repeating - what you're looking in figure 6 is an actual metabolic imprint of the external environment on to the structure of the brain at the cellular level, half to the left and half to the right, and the fascinating details of just how this image was created are included in the footnotes below as note 4 (4).
Original paper: Tootell RB, Switkes E, Silverman MS, Hamilton SL (1988) Functional anatomy of macaque striate cortex. II. Retinotopic organization. J Neurosci 8:1531–1568. Abstract/FREE Full Text: Google Scholar
divided, inverted and distorted with in the visual cortex, from Frisby & Stone (2010), p. 6.
Finally, to end the post is a clip from an interview with the nobel prize winning physicist Richard Feynman, who spent many of years of his distinguished career investigating the fundamental nature of light at the level of photon-photon interactions. During the clip he discusses the phenomenon of vision and the tiny segment of the electromagnetic spectrum that it evolved to detect.
1) al-Haythem wrote the series on optics whilst working at Cairo's al-Azhar Mosque sometime between 1028 and 1038
2) "Apart from that, it is necessary to beware of assuming that in order to sense, the mind needs to perceive certain images transmitted by the objects to the brain, as our philosophers commonly suppose; or at least, the nature of these images must be conceived quite otherwise than as they do: For, inasmuch as [the philosophers] do not consider anything about these images except that they must resemble the objects they represent, it is impossible for them to show us how they can be formed by these objects, received by the external sense organs, and transmitted by the nerves to the brain. And they have had no other reason for positing them except that, observing that a picture can easily stimulate our minds to conceive the object painted there, it seemed to them that in the same way, the mind should be stimulated by little pictures which form in our head to conceive of those objects that touch our senses; instead we should consider that there are many other things besides pictures which can stimulate our thought, such as, for example, signs and words, which do not in any way resemble the things which they signify." Descartes, Optics, Fourth discourse (p. 89 in trans. by P.J. Olscamp)
3) "So that you must not be surprised that the objects can be seen in their true positions, even though the picture they imprint upon the eye is inverted: for this is just like our blind man's being able to sense the object B, which is to his right, by means of his left hand, and the object D, which is to his left, by means of his right hand at one and the same time. And just as this blind man does not judge that a body is double, although he touches it with his two hands, so likewise when both our eyes are disposed in the manner which is required in order to carry our attention toward one and the same location, they need only cause us to see a single object there, even though a picture of it is formed in each of our eyes." Descartes, Optics, Sixth Discourse, trans. P.J. Olscamp, p. 105.
4) Figure 6 shows the results of an experiment in which an anaesthetized monkey viewed a flickering bulls-eye pattern, and was then injected with radioactively labeled glucose (a special type of glucose with a radioactive Fluorine molecule attached). The glucose was taken up in higher amounts by the most active neurons. Area V1 of the visual cortex was then surgically removed and flattened before being used to expose radioactively sensitive film. The result is a picture of regions of activity evoked by the bulls-eye pattern, creating what is known as a 'Retinotopic Map'.