painting.'(Riley in clear detail. Roughly speaking the area of

painting.'(Riley 1984) 
For the purpose of this essay I will look at the optic as the primary sense when viewing Op art and illusion. How we see an object needs careful examination. Understanding the science behind perception, will lay a foundation on which theories and ideas can be safely built upon.

                                              

                                                    Chapter 2

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The science behind perception

 Binocular Single Vision is a term used for how we as humans view and perceive images. It can be interpreted as a situation of blending two separate images from each retina, which then coincide into a single percept. This connection made between seeing and how the brain interprets what is seen, is called fusion. (Webeye.ophth.uiowa.edu, 2017)

Our perception of an image is subjective, it is influenced by utilising our senses and drawing from our personal experiences, our expectations and our cultural backgrounds. Perception allows our brain to organise and translate the data from our senses into meaningful information. Gombrich speaks of visual perception as a process in time. Of how much the eye can take in at one time. He quotes Professor Quastler, ‘What we actually see is a very rough picture with a few spots in clear detail. Roughly speaking the area of clear perception includes less than one percent of the total visual field.’ (Gombrich, n.d.p.50)(Evans, 2006) 
Our perception of what we see is in part phenomenological (experience to be experienced) the conscious understanding gained from an object and of its purpose from the first-person perspective (phenomena). It is also part ontological, (what the experience is) the branch of metaphysics dealing with ‘the nature of being.'(Gombrich, 2000)

Phenomenology
‘Phenomenology is commonly understood in either of two ways: as a disciplinary field in philosophy, or as a movement in the history of philosophy.'(Smith 2017)
The condition phenomenology is also linked to our senses; seeing, hearing etc. as well as encompassing a wider area, by looking at the meaning of things in our lives. Not only our experiences, memory and imagination, but also the meaning of things in our lives, events, tools, objects and our egos. Smith explains this, ‘Conscious experiences have a unique feature: we experience them, we live through them or perform them. Other things in the world we may observe and engage.'(Smith, 2017)
In the first half of the 20th century the movement of phenomenology was proclaimed as the underpinning of all philosophy. The method and nature of the discipline was debated initially by Edmund Husserl and later Martin Heidegger, Maurice Merleau-Ponty, Jean-Paul Sartre.
These classical phenomenologists practiced the analysis of experience, Husserl and Merleau-Ponty were advocates of experience being through knowledge of living life, while Heidegger and his followers believed hermeneutics was the foundation.
 When speaking of phenomenology Merleau-Ponty says, ‘The opinion of any responsible philosopher must be that phenomenology can be practiced and identified as a manner or style of thinking, that it existed as a movement before arriving at a complete awareness of itself as a philosophy.’ (Merleau-Ponty, 1996)
 
Understanding the science of perception helps us to make sense of what we are seeing when encountering an optical illusion. When first looking at an image such as the Fraser illusion below, there will be a mental split between what you know and what you perceive. At first you believe you are observing a spiral, in fact you are looking at a series of concentric circles of diminishing size. This visual distortion is achieved by overlapping arc segments in each circle that terminate at the mid point of the arc segment in any adjacent circle. This produces a visual ’tilt’ which creates the spiral effect (Seckel, 2010)   
                                         Fig.5     Fraser illusion. 
Depth perception occurs when the image hits our retina and we see it as two demential. Our mind is then able to interpret other factors such as distance and shape and then calculate the image into a three dimensions. We do this by using binocular and monocular cues. Receiving slightly different images through the retina, the brain then calculates the differences and judges the distance. Monocular cues determine the scale and distance of an object, linear perspective, texture gradient and the interposition of the object helps evaluate the position of the subject. 
                          Fig.6
This drawing by visually explains the artists use of depth perception. The drawing recedes backwards into the distance drawing the viewer in because of the perspective of the path, people and trees becoming smaller into the distance.
Another type of optical illusion in art is anamorphosis, an image contorted or twisted out of shape. it is hidden and unique, unless you view the anamorphic art from the right angle, it is impossible to make out the image and it’s meaning. Holbein’s painting ‘The Ambassadors 1533’ is a good example of this.   

When first viewing this painting you notice a strange shape central to the bottom, a long stretched sphere, a glitch in an otherwise traditional Renaissance depiction showing learned men with books and instruments. When you stand to the far right you become aware of the perspective and of the actual meaning, magically a skull is revealed.(Nationalgallery.org.uk, 2017) 
                                   Fig.8                             Bridget Riley Nataraja 1993

Bridget Riley’s work is illusional through its repeat and colour rhythms, constantly changing but at the same time remaining in harmony. We perceive the pictorial energies through the grouping of colours and the repeat of line, which become active, throwing off energy with the variables involved. This interaction between the colours happens at the edge of a shape or line. Maximum juxtaposition between and minimal bulk of the shape provide a vehicle for the essential nature of colour to react against each other. Riley’s paintings have a harmonious quality, they feel safe in a visual melody that we understand, a positive ‘Gestalt’ with a beating heart of continuous pattern.

D.W. Hamlyn. Professor of Psychology and author states, ‘Perception may not denote a single concept but rather a family of concepts, which, whilst related needs to be distinguished from each other.’ (Hamlyn, 1979.p.6) Whilst reading Hamlyns book ‘ Studies in Philosophical Psychology,’ It has become clear to me that the question of Perception is an immeasurable undertaking. For the purposes of this dissertation, I will concentrate on one theory, I will examine the Gestalt psychology. Through this theory I will endeavour to understand our perceptions through a structured set of laws. Endeavouring to make sense of what we see in a world of disordered images.