Art Illusions and the Visual System

Introduction

Over time art has been redefined through a scope of various methods and techniques. It is the combined understanding of the visual system and how certain perceptive points can be altered to create artistic illusions. This report outline seeks to explain the techniques artists use to trick the visual process and the factors that determine how the visual system functions.

Intersection of Art and Science

“Study the science of art. Study the art of science. Develop your senses – learn how to see. Realise that everything connects to everything else.” — Leonardo da Vinci (Green, 2018)

History has seen many draw parallels between art and science. Nearly opposite in nature, Art is the imaginative flow of the conscious while science is the methodical outlook on reality. Leonardo da Vinci is one of those artists who has mastered the trick; in order to illustrate the world on canvas, there is a need to first understand it (Green, 2018).

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It can be said that the conception of art is the result of the artist’s subjective expression, however this expression is also dependent on the observer’s own subjective preference (Gudeim, 2019). In other words, is art a deceptive medium of expression? Does art fabricate the real world? Even though the relationship between an artist’s painting and the real world are held on by loose threads, the issue does not disregard a perspective on reality through a visual stance (Gudeim, 2019)

Recent researches have shown that the “brain constantly rewires itself based on how people experience the world from one moment to the next”(O’Brien, 2014).

It is an intriguing observation when people stand transfixed before a painting, when Mona Lisa’s smile makes hundreds of people fly cross country to see its magic and when some would be absorbed by the intricacies of a Van Gogh painting, while others would shrug it off meaningless. The objectives at play are the visual experiences an observer goes through while they perceive the artwork.

How do we SEE Art?

The starting point of vision is the eye. The eye includes the retina and other functional features that transmit signals to the brain to interpret vision. The retina comprises of rods and cones, while the optic nerve has fibres that contribute to the overall composition (Fig 1.) (Marmor, 2015).

Researchers argue that the process of seeing is a result of our unique interpretation of ambiguous sensory information. To confirm this statement, the sole existence of a visual illusion where assumptions are made based on tricks and bias present in perception, even though the observer is completely aware of what is happening supports the argument. (Gregory, 1997,Gregory, 1998,Eagleman, 2001 as cited in Rodrigo Quian Quiroga, 2011).

When visual information is received, it is transmitted through neural firing patterns in the retina to be further processed by the cerebral cortex (Kandel E. R., 2000). The reason why art is so attractive is because it delivers a subjective personal experience to those who observe art (Rodrigo Quian Quiroga, 2011)

Figure 1: The Components of the Eye

To further understand, there are laws that define the relationship between Art and the Visual system.

All art that is visually perceived follows the principles of the visual system (Zeki S, 1994)

–          Law 1: An image of the visual world is not impressed upon the retina, rather it is assembled together in the visual cortex. Responsible for various visual phenomena’s including visual motion (Zeki S, 1994)

–          Law 2: The functional specialization of the visual cortex is to absorb the visual scene and process it in geographically separate parts of the visual cortex (Zeki S, 1994)

–          Law 3: The attributes within the visual cortex process the information individually in the cerebral cortex responsible for vision. The processing disintegrates components of form,color,motion and depth (Zeki S, 1994)

Research shows that no theory can be based on aesthetics without an understanding of its neural underpinnings (Zeki, 1999 as cited in Chatterjee, 2011). It was suggestive that the nervous system and artists have similar points of interest. The nervous system decomposes visual information into different components such as color, luminance and motion (Zeki, 1999).

In respect to this, several artists are known to isolate these attributes such as Alexander Calder who articulated motion, Georges Seurat who emphasized colour and luminance.

Artistic Techniques to “trick the eye”

Using the fundamental knowledge of vision, artists have learned the art of manipulation. There are several techniques used to ‘trick the eye’ and have been identified as signature patterns of the artists themselves. Through analysing the works of Claude Monet, Salvador Dali,Georges Seurat and Bridget Riley will provide an insight into the artist’s flare for deception and how they are perceived.

Monet and the Illusory effect of colour and depth perception

During the change of the 20th century, Monet had painted over 40 different versions of a scenery; this was the Waterloo Bridge over the Thames river (Fig 2.) (Valich-Rochester, 2018).

The main highlight of this painting drifted away from the subject of focus itself. Monet’s focused on the details of the background instead. Research derived explains the complexity of the visual system through highlighting the key distinct features in Monet’s process and intricacies of his work (Valich-Rochester, 2018).

Figure 2:The Waterloo Bridge (1903) by Claude Monet

The visual system processes colour through a pathway of absorbing the wavelengths of light which is then interpreted by the brain.

When the eye perceives colour, it does so through three types of cones present in the retina. S-cones (blue) are sensitive to shorter wavelengths, M-cones (green) are sensitive to medium wavelengths and L-cones (red) are most sensitive to longer wavelengths (Fig 3.) (Valich-Rochester, 2018).

Simple in composition, yet these three types of cones help form the perspective of complex combinations of colour.

Figure 4: Signal Transmission of the Waterloo Bridge

            Figure 3: Colour Perception of The Waterloo Bridge

Once the retina receives information it is then transmitted through signals to the visual cortex (Fig 4.) This lies in the back of the brain, while signals are sent back and forth, other parts of the brain involved in memory, attention and experience help deconstruct the information.

The brain then integrates the information with sensory information from the eyes into categories of line, shape and depth, therefore constructing it into objects and scenes (Williams, n.d. as cited in Valich-Rochester, 2018).

Based on the understanding, what are the tricks Monet uses?

One method of deception Monet applies is the three-dimensional effect on a two-dimensional canvas. The visual process in this case is similar (Tadin, 2018). “Our eyes are curved, but essentially a three-dimensional world gets projected—upside down—to a flat retina” says Duje Tadin (Tadin, 2018). To correctly process the image, the brain turns it right side up and creates connections. However, there is a third element missing from the equation.

Monet “tricks” the observer by providing the missing third element as light, shadow and contrast. These produce the illusion of the bridge as a three-dimensional object (Tadin, 2018). Along with that, the background of smokestacks is given more importance of work as Monet details elements farther away to be small and faded or blurry to imply a sense of depth.

Self-conscious may know that the painting is an illusion, yet it is perceived to be in a three-dimensional form as it is the closest relation to the real world in itself. At first glance, the brain picks up the form of the bridge, the river beneath and the smokestacks much before the finer details are noticed such as Monet’s individual brushstrokes of colour (Tadin, 2018).

“The goal of our visual perception is not to give us an accurate picture of the environment around us but to give us the most useful picture, and the most useful and the most accurate are not always the same.” (Tadin, 2018).

When viewing the painting, illumination plays an important role in altering the perception. This happens due to the combination created when the eye views the art. It captures the illumination falling on the point of interest as well as the intrinsic characteristics of the object itself. In terms of light in the Waterloo Bridge painting, Monet uses a mixture of pigments that have varying properties such as; brightness, hue and intensity. Here the principles of additive and subtractive colour mixing are used. Monet’s clever execution of placing colours next to each other without fully blending them makes the observer see the illusion. Same colour will tend to appear differently when placed next to different colours (Williams, n.d.). This method has been adapted by several artists to creating a depth of field effect in two dimensional artworks.

“A lot of the motion in Monet’s paintings comes from the fact he used equal luminescence,” (Livingstone, 2002)

Salvador Dali and Paranoiac-critical effect

Salvador Dali, a renowned Spanish surrealist artist had aimed to blur the distinction between the real and the imagined (Susana Martinez-Conde, 2015). Dali introduced illusions into his artwork to further challenge his observer’s perspective to see beyond the surface of paint.

Components like brightness, contrast, colour, shading and eye movements contribute to affect what the observer sees. Dali noted that what is visually interpreted of reality is moreover based on the habits of the mind than the eye. He understood that we create an ordered or disordered world from intermittent and incomplete retinal information processed by our mind’s experiences, desires and apprehensions (Martinez-Conde S., 2012). The Gestalt laws were conceptualized in the early 20th century and one of the principles of closure states our perception will group individual elements as a whole (rather than consider them as separate from each other) if they seem to complete an entity (Martinez-Conde S., 2012).

The ability of the brain to reconnect sparse links helps understand the ‘paranoiac-critical method’ invented by the artist Salvador Dali. Paranoia provides a striking example of an illusory contour resulting from filling-in processes (Martinez-Conde S., 2012). Shown as an example is a sketch by Leonardo Da Vinci (Fig 5.)

 

Figure 5: Bust over Pedestal by Leonardo Da Vinci

Figure 6: Thirst by Salvador Dali

While prominently portrayed a bust over a pedestal, the above part of the sketch depicts small figures on horses. Even without a face, a face is perceived immediately. As facial recognition is a dominant perceptual function the brain fills in the missing information thus giving the observer a complete output from the minimal input (Cox D, 2004).

Dali’s own interpretation is seen in Thirst (Fig 6.). An ink blotched painted on paper. The initial objective was to depict two figures from the renaissance period in terms of clothing where one figure is seen to serve wine to the other. With the lack of communication through the medium, the observer still pictures the complete idea. Dali experimented with this method to further create one thing to be another. His goal was to achieve images that could not be analysed or diminished by rational logic (Martinez-Conde S., 2012).

Georges Seurat and Spatial colour mixing

Pointillism is a famous technique first founded and mastered by French artist Georges Seurat. It is a technique where small dots of “pure” colours are used to create an overall effect of “blended” colours when viewed from an appropriate distance (I R Schwab, 2003). In theory the technique is used to “increase the luminosity to achieve an optical blending at the retina level” (I R Schwab, 2003). First demonstrated by Georges Seurat in his famous 1884 painting “A Sunday Afternoon on the Island of the Grand Jatte” (Fig 7.) 

Figure 7: A Sunday Afternoon on the Island of the Grand Jatte (1884) by Georges Seurat

The concept of receptive fields provides the basis of the technique of pointillism. When the painting is viewed at a certain distance, a coloured dot considered ‘pure’ will trigger a cone or group of cones therefore contributing to a centre surround receptive field (I R Schwab, 2003). As distance increases, dots will trigger the receptive field with more colour combinations. In the chance that the colours transmitted are complimentary, the result of the neural signal will portray them as achromatic dull intermediate colour (I R Schwab, 2003).

As the technique is highly mechanical, detailed, and rigid, Pointillism originated as an analytical study of optical colour theory where works produced often appear to be flat, static and lifeless (A study of light; Contrasting Impressionism and Pointillism, n.d.). Pointillists are known to take advantage of the visual system’s two-stream processing (Conway, 2007).

Instead of directly painting a green tree, artists tend to paint coloured dots of green, yellow, red and blues which compose the overall tree form and colour depicting a sense of shimmer or colour change when perceived from a distance.

“As with the other impressionists, the pointillists’ technique works because the part of our visual system that sees color is not adept at locating items in space” (Conway, 2007)

“Some say they see poetry in my paintings, I see only science” – Georges Seurat (Kate, 2018)

Pointillist works are often denoted as bright in overview. This is because the colours used by artists are pure in brightness and luminesce. 

Bridget Riley and perceived motion in static art

Geometry has always played a part in artist works. In the case of creating motion for a static work, simple geometric patters are used to illustrate the illusion.

However, more than the art, it is the function of the eye. Research analysis explain that the illusion that is being observed promotes retinal shifts. These are caused by small involuntary eye movements that the observer makes when trying to find a point of fixation on the perceived artwork (Frouke Hermens, 2012). Further studies have looked into details of eye movements and inferred a prominent role of small rapid position shifts called microsaccades to be responsible for the illusory effect of motion (Frouke Hermens, 2012).

Three research experiments were conducted where participants eye movements were recorded as they perceived variants of Bridget Riley’s Fall painting (Fig 8.), a black and white composition of undulating lines.

Figure 8: Fall by Bridget Riley

The painting was manipulated to differ the strength of induced motion and record the corresponding changes of the eye movements (Frouke Hermens, 2012). Research found other sources of instability in retinal imaging other than the microsaccades. It’s important to consider the oculomotor drift as a potential factor that affects the perspective (Frouke Hermens, 2012).

In order to breakdown how the observer sees motion in static art, the explanation focuses on three main categories of fixational eye movements (Martinez-Conde S, 2006, Martinez-Conde S M. S., 2009, Rolfs, 2009)

The microsaccades are the movements of the eye when it attemts to fixate over a large amplitude usually less than 1 deg of visual angle and high velocity (Otero-Millan J, 2008). The phenomenon of microsaccades occurs in both eyes simultaneously (Otero-Millan J, 2008), the properties are fairly like saccadic eye movements as well.

The presence of slow oculomotor drift relate to larger movements of the eye with velocities that are much smaller than the microsaccades (Otero-Millan J, 2008) (Frouke Hermens, 2012).

There are another set of movements referred to as a ‘tremor’ which are small amplitude movements that rapidly happening in each eye at a time (Otero-Millan J, 2008) (Frouke Hermens, 2012). During the first step there is displacement of the eyes where the projected image is shifted across the retina due to the alternating pattern of black and white undulating lines. The visual system processes and interprets the shifts as motion instead of changes in direction of eye movements (Zanker J M, 2004 as cited in Frouke Hermens, 2012).

How does the observer perceive all the techniques used by artists to trick the eye?

Research says when an observer looks at a painting, simultaneously there are two different pathways of viewing it. The first pathway is a black and white perspective, or better known as the negative and positive spaces, the second pathway is colour (Livingstone, 2002) (Dingfelder, 2010). The visual stimulus starts at the retina and is then transmitted through the visual system. Here the brain segregates the input information of a painting’s colour and brightness. Both those processing points are well separated, like sight and sound (Livingstone, 2002). The visual system adheres to the colour blind aspect which is called the “where” stream and is a common attribute human beings have with mammals.

The “where” stream allows us to navigate our environment and surroundings, to locate things in space and to track any movements we perceive. The “what” stream is the component that allows the observer to process colour information. It is the sole key to helping determine what the object is (Livingstone, 2002).

It can be generalized that artists also use “equal value” of the streams to confound the brain’s perspective (Livingstone, 2002).

The retina is responsible for decoding the visual information with the help of layered neurons to produce a simplified language of understanding visual objects (Fig10.) (Marmor, 2015).However, there is a misjudgement produced while decoding the visual object caused by the observer’s brain properties that concentrate on what is important to recognise while also placing a limit and constraint of perception that ultimately leads to the illusory effect of illusions.

The basis of retinal coding is the ability to recognise contrast. The process of this begins at the level of the photoreceptor cells and the bipolar cells.

Bipolar cells connect the photoreceptors to ganglion cells (Marmor, 2015) These develop receptive fields across the retina which sees the world around us. “The use of high contrast, often showing the subject against a dense dark background (‘chiaroscuro’), was popular for a time in the Renaissance, following the lead of Caravaggio” (Fig 9.) (Marmor, 2015) The high contrast brings the subject of the painting to life.

Figure 9:Saint John the Baptist (1604) by Caravaggio

Figure 10: Sketch of Receptive Field

Figure 11: Cone Sensitivity of the Eye

The retina itself adjusts the brightness sensitivity at any moment in time through the cone photoreceptors that provide the vision. The difference of energy spread between a stimulus and cone sometimes leads to fail of transmission and activation of the cone, therefore resulting in a no response (Fig 11.). In order to readjust to the surrounding ambient lighting of the background the cones move the range of sensitivity up or down accordingly. It happens in mere seconds and the brain receives the signals of recognition (Marmor, 2015)

Conclusion

The eye has complex mechanisms at play when viewing artwork. Through the distinct features of colour constancy, colour perceiving by rods and cones,to perceiving depth and motion in static art portrays the intricate details behind the visual system’s functions. Illusions of varying types are perceived with a combined knowledge of colour, brightness, contrast, depth, motion and other minute factors that contribute to the overall effect. Artists have well understood the mechanism and dwell into more methods to entice the visual process. By doing so, ensuring that the constant development of artistic techniques draw more connections to neuroscience and vice versa.

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