Science of Perception

Current scientific thinking about visual experience tends to conform to what could be called the ‘standard view’ (SV). SV can be summarized as follows:
1.
There is an external world full of objects and events with properties that exist independently of our seeing them.
2.
Our visual system creates an internal representation, or model, of objects and events in the external world, and it is this model we subjectively experience.
3.
Our visual experience of the world is, therefore, distinct from the objects and events in the world itself.

Many vision science textbooks endorse SV by claiming the biological function of vision is to accurately represent or model the real world, assuming there is a given state of reality to represent. In what is one of the most widely referenced textbooks on vision, Stephen Palmer states
the evolutionary purpose of vision is achieving vertical knowledge of external objects and events, in order that perception is ‘…consistent with the actual state of affairs in the environment.’ Meanwhile the eminent neuropsychologist Chris Frith , writing about how the brain ‘creates our mental world’, says: ‘When I look at a tree in the garden, I don’t have the tree in my mind. What I have in my mind is a model (or representation) of the tree constructed by my brain.’

Artists who have thought deeply about these matters have explicitly rejected SV, and the various ontological assumptions it entails. Georges Braque (1882-1963), the co-founder of Cubism who spent much of his life analyzing visual experience, said towards the end of his career: ‘You see, I have made a great discovery: I no longer believe in anything. Objects don’t exist for me except in so far as a rapport exists between them, and between them and myself.’ For Braque, objects in the world don’t exist independently of our perceiving them; the object and our experience of the object are one in the same. He wrote: ‘A thing cannot be in two places at once. You can’t have it in your head and before your eyes.

(adapted from http://goo.gl/pey4wV)

Perception

Perception

[per-sep-shuh n]
noun

1.
the act or faculty of perceiving, or apprehending by means of the senses or of the mind; cognition; understanding.
2.
the result or product of perceiving, as distinguished from the act of perceiving; percept.
3.
a single unified awareness derived from sensory processes while a stimulus is present.

Perception may be categorized as internal or external.

• Internal perception (proprioception) tells us what is going on in our bodies; where our limbs are, whether we are sitting or standing, whether we are depressed, hungry, tired and so forth.
• External or Sensory perception (exteroception), tells us about the world outside our bodies. Using our senses of sight, hearing, touch, smell, and taste, we perceive colors, sounds, textures, etc. of the world at large. There is a growing body of knowledge of the mechanics of sensory processes in cognitive psychology.
• Mixed internal and external perception (e.g., emotion and certain moods) tells us about what is going on in our bodies and about the perceived cause of our bodily perceptions.

The Science of Seeing

The Eye
The outer shell of the eye, called the sclera, is the white rigid spherical shell that gives the eye its structure. The sclera itself is opaque to allow light into the eye. It merges in the front with the transparent cornea, which is the window of the eye. The cornea has an index of refraction of about 1.37. Immediately behind the cornea is the aqueous humor, a clear watery liquid which supplies the cornea with the nutrients it needs since blood vessels in the cornea would affect the optical clarity.

The Pupil
The pupil is the opening in the center of the iris that controls the amount of light entering the eye. The iris merges with colored connective tissue called the choroid which lines the inside of the sclera. In humans, the pupil is circular whereas horses and goats have a horizontal slit. Snakes, alligators and cats have a vertical slit.

Tiny muscles on the iris automatically adjust the size of the pupil within tenths of a second depending on the light level. It is interesting to note that the pupils of both eyes will open and close in unison, even if only one is stimulated with light. This is due to the consensual pupillary reflex. In addition, our attitude about what we are seeing also influences the size of the pupil. This effect, common when viewing pictures of attractive members of the opposite sex, can affect the pupil size by up to 30 percent.

The Lens
The lens, which is immediately behind the iris, provides fine focusing to adjust for the object distance. This process is called accommodation and is accomplished with a ring of muscles around the lens. When the muscles are relaxed for viewing distant objects, the lens is relatively flat. When the muscles constrict to view objects close up, the lens changes shape, becoming more curved.

The near-point is the closest point where the eye can still focus. This distance increases with age as the lens gradually looses elasticity. This distance usually surpasses the our arm length between the ages of 50 and 60, which then calls for corrective lenses. Cataracts, or a loss of transparency of the lens, also affect many people as they get older.

Vitreous Humor
The inner chamber of the eye is filled with a clear jellylike substance known as the vitreous humor. This structureless substance has an index of refraction close to that of water. Sometimes when you look carefully, you can see bits of cellular debris in the vitreous humor called floaters that give a faint shadow to the image you see.

The Retina
The retina, or light sensitive part of the eye, covers the back of the eyeball and is the final destination of the light. The lens and cornea actually invert or turn the image displayed on the retina upside down in the process of providing a clear image that is in focus.

(adapted from: http://www.eye-therapy.com/)

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TL;DR
Human vision is an incredibly complex process that involves the eyes, nerves and brain all working together to translate visual stimuli into visual information.

Seeing [defined]

See

[see]
verb (used with object), saw, seen, seeing.

1.
to perceive with the eyes; look at.

2.
to view; visit or attend as a spectator: to see a play.

3.
to perceive by means of computer vision.

4.
to scan or view, especially by electronic means: The satellite can see the entire southern half of 
the country.

5.
to perceive (things) mentally; discern; understand: to see the point of an argument.

6.
to construct a mental image of; visualize: He still saw his father as he was 25 years ago.

7. 
to accept or imagine or suppose as acceptable: I can’t see him as president.

Synonyms
observe, notice, distinguish, discern, behold, regard, .comprehend, penetrate, determine, know, undergo, accompany

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TL;DR

Seeing is not restricted to processing visual information/stimulus. Seeing also constitutes perception and perceived mental imagery.

Seeing depends on context, desire and expectation. Does visual information provided by the eye always yield the same stable interpretation?