The eye in diagrams

The surprising eye

The eye is full of surprises. The biggest ones come from the structure of retina that is situated at the back of it. The purpose of this Post is to provide a link to images and explanatory captions that tell us more about this starting gate of visual processing. At first sight, much of what we find strikes us as bizarre. But, when we delve more deeply, we discover the considerable advantages of the way things actually are. It turns out that nothing would work nearly as well as it does, if things were arranged any differently. The images and their captions will go a long way towards explaining why.

In the process, they will help readers to get a better understanding of how the eye/brain combination makes practical use of the information contained in the ever-changing patterns of light coming into the eye.

The link to the diagrams

Click on the link below to access the images and captions referred to. They are extracted from ‘The Glossary‘ to the four volumes I am in the process of publishing on this website.

 

GLOSSARY DIAGRAMS (1)-THE EYE

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What happens next

Upon leaving the retina, the neural signals travel in two directions. Some go up the optic nerve to the region of the neocortex known as ‘Visual Area 1′. Others take a completely different route that makes contact with the regions of the “Old Brain”. These play a central role in visual perception as we experience it. For example, they play their part in eye movements, spatial awareness, affective responses, multimodal processing, whole-field relations and much besides. Images and captions relating to both these routes will be posted later on this website, in a separate entry, entitled, “Visual Regions in the Brain”.

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Images of blood vessels, neurons and and neural processes in the eye.

The human retina contains a very large number of neurons (cells) and a very much lager number of neural of processes providing links between them. It also features a dense network of blood vessels that supply blood to the neural processes. Together these three components make a significant barrier to the passage of any light that strikes the receptors. Until I learnt better, this light-blocking function did not seem to be of much of interest.

What changed my mind was the discovery that the light-sensitive cone and rod receptors that transform light-energy into neural signals, do not face towards the incoming light, but away from it. Consequently, the light coming into the eyes has to penetrate this light-impeding layer of neurons, neural processes and blood vessels, before it reaches the receptors. To add to my surprise, it turned out that the light-receiving end of the receptors is buried in a layer of dark matter. It was some time before I realised how these seemingly bizarre arrangements make possible visual perception as we know it.

The barrier confronting the light that enters the eye

It turns out that the barrier of neurons, neural processes and blood vessels compensates for the fact that the rod receptors are very much more sensitive to light than the cone receptors. The benefit of this state of affairs is that it enables a necessary degree of functional equality between the responses to the incoming light of the two different receptor-types. Needless to say, this equalling up would not take place, if the light striking the less sensitive cone receptors were to be subjected to the same impediments. This explains why the forces of evolution have created a gap in the neuron and blood vessel barrier in front of the region known as the fovea, exactly where the incoming light strikes the cone receptors.

Glare-blindness

If the equalling up process did not take place, the rod receptors would be bleached out whenever the incoming light was strong enough to activate the cone receptors. The result would be a massive degree of glare-blindness in daylight conditions.

Dire consequences

If they were effectively blind, the rod receptors would not be able to participate in daylight visual processing. As a consequence, the neural computations of whole-field relations could take place. One of the many aspects of visual processing that would rendered impossible would be the separation of reflect-light from body-colour. As a result there would be neither colour constancy, nor the use of the information residing in the  reflected-light that has been separated out.

If this were so,  pretty well all that I have written in my book “Painting with Light” would be nonsense.

Burying the receptors in dark matter

The burying of the light-sensitive receptor heads in the dark matter is easier to explain. It prevents the light from scattering from one receptor to the next and, consequently, reduces blurring.

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The eye
Figure 1: Blood vessels blocking light from the ‘rod’  photosensitive  receptors.  The small darker disc is where the light sensitive ‘cone’ receptors are located. Notice that no blood vessels impede the passage of incoming light to these.

 

The eye
Figure 2: This image of a small section of a network of neural processes gives an inkling of an idea of the extent to which these these can block the incoming light.  For reasons explained above, the blockage only applies to ‘rod’  photosensitive receptors. It does not apply to the ‘cone’ photosensitive receptors .

 

The eye
Figure  3: A diagram of cell-types in each of the five layers of the retina. The massive numbers of each of these contribute to the blocking of the light arriving at the ‘rod’  photosensitive receptors.

Some numbers and sizes

One estimate for the number of the light-sensitive receptor cells is in the region of 150 million. Although the precise number of neurons and neural processes in the retina is unknown, it is certainly in the hundreds of millions.  All this packs into an astonishingly thin layer (less than 0.5 mm) whose extent can be compared to that of a 10p piece.

 

A reference

If you want a comprehensive account of the component parts and structure of the retina, you could consult the relevant pages of the website of the The National Library of Medicine.  You will find them dizzyingly more complex than the grossly oversimplified information given either above or in the ‘Glossary‘ extract.

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Shading and surface form

What colour are shadows and shading?

This POST provides a link to “Shading  and surface form”, Chapter 27 of my book “Painting with Light and Colour”. It may surprise many that it comes in PART 2, which is dedicated to painting with colour. The reason is that the visual systems that are used to create colour consider blacks, whites and greys to be colours and, accordingly, they treat the blackness, greyness and whiteness of shadows, shading and highlights as colour.

Surface-solidity, spatial-separation and ambient-allumination

However, this fact of visual perception does not mean that the reflected-light does not provide information to other visual systems, working in parallel. In particular, the systems that tell us about surface-solidity, spatial-separation and ambient-illumination continue to perform their function. As explained in PART ONE of this volume, although they enable us to sense these properties, they never make them visible in the way body-colour is visible.

The problem of invisibity

The “invisibility” of these properties confronts artists trying to represent them with the seemingly insoluble problem of deceiving the eye/brain into “seeing” something that they cannot see. Luckily due to the research of Seurat, Cézanne, Bonnard, Marian Bohusz-Szyszko and others, a simple and, accordingly, practical resolution of this seeming paradox is available. Moreover, due to research undertaken by myself and colleagues, its efficacy can be explained in scientific terms (see many chapters in Book One of this volume and Chapters 13 and 14 of “What Scientists can Learn from Artists”)

The solution

The practical solution provided to me by Professor Bohusz-Szyszko is to ensure (a) that there should be no repetitions of colour in any part of the surface of paintings and (b) that all the paint that is actually visible to viewers of the painting should be made up of mixtures containing some proportion, however small, of complementary or near-complementary, pigment colours. In this conntext,  it is important to emphasise  that this solution should be kept in mind when painting shadows, shading and highlights.

CHAPTER 27 – SHADING AND SURFACE FORM

Two images and a question to consider

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Cowslips and violets

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Flowers in a vase

Question: Do all the “mistakes” and inconsistencies in the “flowers in vase” painting matter?

Other relevant chapters from Book 2: “Painting with Colour”

Other relevant Posts on colour and light in painting:

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The integrity of the picture surface

Google says that the “integrity of the picture plane” is a phrase coined by the influential art critic Clement Greenberg in his essay “Modernist Painting”. It concerns the issue as to whether the fact of creating an “illusory pictorial space” interferes with perceptions of the “objectness” of the actual picture surface.  This was a question of primary importance to the “Early Modernists” from the late 1860s onwards. For them, as explained in  Chapter 6 of my book “Fresh Perspectives on Creativity”, the fact of the possibility of being aware of the actual surface of paintings was one of the reasons for what they believed to be their inherent superiority relative to photographs. Their belief was that, since “deception is immoral”, painters must avoid it at all costs. Despite the difficult-to-comprehend nature of this evidently questionable argument, it stuck for about a century. Thus, in the 1960s, it was still a potent aspect of the teaching of my two mentorsProfessor Bohusz Szyszko and Michael Kidner.  The difference between the “Early Modernists” and Clement Greenberg was that the former (and  Professor Bohusz-Szyszko) thought it possible to depict illusory pictorial space without destroying the integrity of the picture surface. In contrast, Clement Greenberg asserted the impossibility of any such thing, as did Piet Mondrian and a number of earlier painters, plus a whole list of later artists, including Michael Kidner and Ellsworth Kelly.

As those who have read “Painting with Light”, the first Book in this Two Book Volume (see contents list), will realise, the early Modernists and Professor Bohusz-Szyszko got it wrong. The use of unmixed repeated colours did not disrupt the picture-surface, but rather the illusory pictorial space. They do so because our eye/brains read them as being on the picture surface and, consequently, as jumping out in front of any illusory pictorial space. It is thus, the integrity of illusory pictorial space that is disrupted.

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Two paintings that illustrate different meanings of the phrase “integrity of the picture suface”

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Cézanne: one of the Fôret du chateau noir paintings

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picture surface
Ellsworth Kelly : Shaped painting on gallery wall – an experience of pure red

 

 

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Thin lines

A confluence of issues

This Post introduces Chapter 22 from my book “Painting with Light and colour”. It uses one of my paintings to discuss many issues that relate to viewing conditions.  These all apply to all paintings, but it is difficult to find information about them in other books. Indeed, it was not until I began work on paintings including numbers of thin lines that I became fully aware of many of them. My awakening was a result of the coming together of many strands of the story I have been telling in my series of four books.

  • The dogmas of Marian Bohusz-Szyszko (see Chapter 1),
  • The “systems” ideas of Michael Kidner (see Chapter 8 of my book on “Creativity“),
  • My interest in the debates relating to “illusory pictorial space” (see Chapters 7-10 in “Painting with Light”, the first part of this volume),
  • My interest in the Modernist Painters obsession with what they described the “integrity of the picture surface”* and its dynamic implications in the history of “Modernism in Painting**
  • The use of thin lines as a means of exaggerating and, thereby, exploring “simultaneous colour contrast effects” (see previous chapter).

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Important warning

In general, whenever images of paintings are transferred to the computer screen, many of their qualities are lost. Sometimes this can be an advantage, but never for paintings that follow the dogmas of Professor Bohusz-Szyszko. This is particularly true for the images using thin lines discussed in this chapter and the next. Often, you will just have to take it on trust that the effects discussed are as described.

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An image of a painting with twelve of orange thin lines

Pictorial space

CHAPTER 22 – MORE ON THIN LINES

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Footnotes

* If you ask Google “What is a Modernist painter”, you get the following excellet summary:  Modern art includes artistic work produced during the period extending roughly from the 1860s to the 1970s, and denotes the styles and philosophies of the art produced during that era. The term is usually associated with art in which the traditions of the past have been thrown aside in a spirit of experimentation.” However, if you had asked Manet, Cézanne, Van Gogh,  Matisse, etc., etc., whether traditions of the past had been thrown aside, you would find that it was by no means all of them.

** Google says that the “integrity of the picture plane” is a phrase coined by the influential art critic Clement Greenberg in his essay “Modernist Painting”. It concerns the issue as to whether the fact of creating an “illusory pictorial space” interferes with perceptions of the “objectness” of the actual picture surface.  This was a question of primary importance to the “Early Modernists” from the late 1860s onwards. For them, as explained in  Chapter 6 of my book “Fresh Perspectives on Creativity”, the fact of the possibility of being aware of the actual surface of paintings was one of the reasons for what they believed to be their inherent superiority relative to photographs. Their belief was that, since “deception is immoral”, painters must avoid it at all costs. Despite the difficult-to-comprehend this questionable argument, it stuck for about a century. Thus, in the 1960s, it was still a potent aspect of the teaching of my two mentorsProfessor Bohusz Szyszko and Michael Kidner.  The difference between the “Early Modernists” and Clement Greenberg was that the former (and  Professor Bohusz-Szyszko) thought it possible to depict illusory pictorial space without destroying the integrity of the picture surface. In contrast, Clement Greenberg asserted the impossiblilit of any such thing, as did Piet Mondrian and a number of earlier painters, plus a whole list of later artists, including Michael Kidner and Ellsworth Kelly.

As those who have read “Painting with Light”, the first Book in this Two Book Volume will realise, the early Modernists and Professor Bohusz-Szyszko got it wrong. The use of unmixed repeated colours do not disrupt the picture-surface, but rather the illusory pictorial space. They do so because our eye/brains read them as being on the picture surface and, consequently, as jumping out of any illusory pictorial space, which is allways behind it. It is thus, the integrity of illusory pictorial space that is disrupted.

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Earlier chapters from “Painting with Light and Colour”:

Painting with Colour: Introduction

This Post provides a link to the introduction to BOOK 2 of “Painting with Light and Colour“. It deals with what I have described as “body colour” and is  subivided into four PARTS:

  • Part 1: Colour and feeling (Chapter 19).
  • Part 2: Local colour interactions (Chapters 20-24)
  • Part 3: Shadows, shading and highlights (Chapters 25 -28)
  • Part 4: Concluding syntheses based on both “Painting with Colour” and “Painting with Light”( Chapters 29-31)

INTRODUCTION TO BOOK 2: “PAINTING WITH COLOUR”

 

Three paintings

These provide illustrations of a small proportion of the subjects touched upon:

Light, colour and Chiaroscuro
Figure 1 : Colour, Light and shade : The Esplanade, Castelnau de Montmiral – Chalk pastel

Light, colour and Chiaroscuro
Figure 2 : Colour and Light : Breath Pastel No 18

Light, colour and Chiaroscuro
Figure 3 – Colour only – mixed media – Michael Kidner

List of already Posted chapters from “Painting with Light”:

Other Posts on colour and light in painting:

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Colour contrast effects

Simultaneous Colour Contrast

This Post introduces Chapter 21 of my book “Painting with Lightand Colour”. It focuses on a subject that is dealt within every book, every article and in every classroom in which the subject of colour dynamics is treated. It was first described by Michel Eugène Chevreul in 1839. The name he gave to it was “simultaneous colour contrast“.

Its potential for use in paintings was popularised by Eugene Delacroix. It was picked from him by the Impressionists and many of their Modernist Painter successors. In the twentieth century when so many artists turned to non-figurative productions, it came to be treated as a subject in itself. A particularly influential part in this process was played by teachers at the Bauhaus. Of special importance were Johannes Itten and Joseph Albers, both of whom produced  books exploring the possibilities of colour contrast effects . Both had a widespread and lasting influence on artists and art education. The purpose of this chapter is to introduce their ideas as a preparation for going beyond them. Doing so will provide the subject matter for this chapter as well as chapters 22, 23 and 24.

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CHAPTER 21 – LOCAL INTERACTIONS

Three paintings exploring colour-contrast effects

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Joseph Albers : from homage to the square series

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Robin Denny: Baby is three

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Mark Rothko: Violet Green and red

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A lot more about colour-contrast coming shortly

Chapte 22 : Thin Lines

Chapter 23 : Viewing conditions

Chapter 24 : Colour and surface.

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Earlier chapters from “Painting with Light and Colour”:

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