Seminar Paper, 2015
18 Pages, Grade: 1,3
2. Basics of perception and vision
2.1 What is perception?
2.2 Facts about vision
3. The evolution of vision
4. The concept of vision
4.1 Structure and function of the human eye
4.2 Neurology of vision
List of illustrations
Today, in our fast moving, computer-driven lives we are exposed to a myriad of sensations every second and not only from the environment or nature around us but also from ceaseless attacks through our modern media, that is mostly based on visual stimulation. So the topic of perception is, although it has been dealt with throughout the centuries from the stoic philosophy of the Greeks to modern neurologists, a highly current one that affects us all and every day in an unprecedented way.
Not least as a popular American crime drama television series with the title “Perception”, where an eccentric neuropsychiatrist uses his unique perception abilities to solve complex criminal cases and a modern theatre play “Molly Sweeney” by Brian Friel, on stage at the moment at Theater Lindenhof in Melchingen, Germany, where the protagonist, a young woman, regained her eyesight through an operation and could not cope with the overwhelming sensations, show the current fascination of the topic.
In the following chapters I will draw attention to the basic principles of perception, especially visual perception as well as the evolution, concept and the functioning of our eyes to come to a better understanding of how we see things and the way our visual perception works.
The Cambridge Dictionary gives in fact two different meanings for this term: Firstly, perception is described as “the quality of being aware of things through the physical senses, especially sight” (Cambridge Dictionaries Online, n.d.) and it adds that drugs can alter our perception of reality. Secondly, the term perception also means belief, a belief or opinion that many people hold based on how things seem to be. For example can photographs or a film affect people´s perception of war or other events in the past (cf. Cambridge Dictionaries Online, n.d.).
These two definitions do not exclude each other. We rather experience perception as a process starting with a stimulus and leading to a person´s subjective understanding of the world. But this is not a simple process; it involves the processes of identification, interpretation and organization of information (cf. Goldstein, 2002, p. 1-3). In other words, perception is our sensory experience of our environment and it involves the recognition of environmental stimuli as well as the action taken in response to these stimuli. The perceptual process also delivers information about elements of the environment that may be critical to our survival. Thus perception “creates our experience of the world around us, it allows us to act within our environment” (Cherry, 2014).
Perception is experienced predominantly by the five classical senses of human beings: Sight, Touch, Smell, Taste and Sound. These are completed by a multitude of other senses like the feeling of hot and cold, that means temperature, the capability of keeping balance, for example when standing on one leg or by riding a bike, the feeling of pain and the kinaesthetic sense, the awareness of muscular movement and position, that tells you for example which hand is closer to the telephone when it rings or helps to find your mouth when eating with knife and fork or let you touch your nose with your finger even with closed eyes. Moreover, there are many internal senses which are for example responsible for breathing or the gag reflex or the sense of time (cf. Campenhausen, 1993, p. 4).
As the definitions above imply, perception is not just a passive receipt of signals, but it is the result of an active work of our brain, and as we will see influenced by memory such as recognizing a familiar person in the street, expectation and attention.
But before we immerse into the details of the perceptual process, which will be explained in the fourth chapter, I want to draw attention to some fascinating facts about vision in general and give a short overview over the process of evolution of vision and over the structure of the human eye and how it works.
“Eyes are more exact witnesses than ears,” (Diels/Kranz, 1992, B101a), stated the Greek philosopher Heraclitus and interprets vision as more important than all the other senses. There are different types of humans, who recipe their environment in different ways, some are more auditory, some more kinaesthetic or auditory-digital or even olfactory orientated. But for all of them vision is very important and for the big majority of human beings seeing is the predominant way to get information about the surrounding (cf. Thompson-Schill et al., 2009; Walter, 2013, p. 25-29).
This is not surprising as the human eye and the associated neurological system is one of the most complex organs and is able to distinguish about 50,000 shades of grey and 10 million colours and can in ideal conditions see up to 576 megapixels For comparison, an average camera is equipped with only 12 to 20 megapixels (cf. Scriba, 2007, p. 1-2). To evaluate this data, each eye sends about one gigabyte of information to the brain per second and our brain is able to process it in just a fraction of a second which requires about half of the brain to get involved (cf. Gröne, n.d.).
Animals as well as humans use eyes for their visual perception. Looking at animals we can discover a wide variety of different kinds of eyes (about 40 to 60 different kinds). Pictures 1 to 3 show the three most popular forms: The camera eye of the vertebrates with a lens (1), the complex facet eye of insects (2) and the mirror eye of the scallop (3) (cf. Goldstein, 2002, p. 216; Gehring, 2012).
In his book “On the Origin of Species”, published in 1859, in which Charles Darwin developed his theory of evolution he wrote a whole chapter about the eyes and the ability to see. In the years of research he discovered and was fascinated about the different types of eyes of animals.
He had a problem explaining the existence of the sense of sight, because for him it appeared unlikely that something as elaborated as for example the eye of an eagle has developed just because of genetic variation and natural selection. With regard to the different types of eyes working completely differently he found it even more unlikely that every single sort of animal with special eyes has accidentally brought forth a unique kind of eye (cf. Gehring, 2012).
For a long time and sometimes still today the existence of the eye was used as a proof for an intellectual design and thus the existence of god instead of evolution and natural selection.
Darwin could not fully explain the development of the eye. He himself felt that something was missing. But he was convinced by his theory of evolution so at some point the eye must have developed. Because he could not believe that the incident of creating an eye has happened independently for more than once, Darwin´s thesis was that at a very early point of the evolution there was a very simple form of an eye consisting of just two cells that provided a selective advantage and from this prototype all different eyes have developed. He could not prove this thesis, but actually he was right (cf. Gehring, 2012; Goldstein, 2002, p. 127).
Many scientists after him took another view of it. Until 1995 the common opinion was that the eye in fact developed in a convergent way so at least 40 to 60 times independently from each other. But in 1995 the Swiss developmental biologist Walter Gehring discovered the master gene Pax6 which seems to be the starting point for the development of the eyes of all animals. With a multitude of experiments Gehring and his team could show that with this master gene they could control the eye development in all conceivable kinds of animals. So, with different mutations of the gene, they could grow mice without eyes when they deactivated the gene and even flies with additional and functioning eyes on different parts of their bodies, for example on their legs or on their wings.
The results proof that the programme for developing eyes is the same within all animals and human beings and all different kinds of eyes have indeed evolved from one point. Thus, Darwin´s thesis was perfectly confirmed, if only 100 years after his death (cf. Gehring, 2012).
As we have seen in chapter three there are different types of eyes, but in all cases vision is based on light and optical refraction. We will now take a closer look at how the process of seeing actually works and for that we will concentrate on the human eye. Picture 2 shows the most important parts of the anatomy of the human eye.
Firstly, there are muscles around the eye that control the angle and are the most active muscles in the human body. The transparent cornea protects the pupil and the iris and helps together with the lens to focus the light, we will see that later. Directly behind the cornea is a coloured ring-shaped membrane called the iris. The iris with its adjustable circular opening, the pupil, regulates the amount of incoming light like a shutter. After passing through the lens the light must travel through the vitreous humour before it meets the retina. The retina consists of millions of light sensitive cells which transform the light energy into an electrical nerve signal which then travels to the brain via the optic nerve and eventually forms an image (cf. Stangor, 2012).
There are two classes of cells, rods and cones. Rods are good for black and white vision, they help us to distinguish between light and dark, cones are there for more detailed and colour vision. They need more light to get activated. This is why humans hardly see colours and have only grey scale vision in twilight conditions, when mostly the rods are working. Cones are situated in an area of the retina called fovea. The spot where the optic nerve exits to the brain is called blind spot, because there are no receptors on the retina. When light falls on this spot a potential image cannot be seen (cf. Campenhausen, 1993, p. 137; Goldstein, 2002, p. 39-45).
As we can see in Picture 5 the elastic lens makes it possible to switch between near and far vision by adjusting the refraction of the light. If the focusing does not work properly, sharp vision is not possible and the result is either short- or farsightedness (myopia or hyperopia). About 60% of the population in the western countries need some form of vision correction. These people need glasses or contact lenses as additional lenses so the focal point hits the retina (cf. Florida Lions Foundation for the Blind, 2013; Stangor, 2012). Today an artificial lens or laser treatment can help to regain normal eyesight by changing the index of refraction of the cornea, so that the total refraction is correct again. Studies from Asia, the USA and Europe show that the percentage of short-sighted people in industrialized nations increases dramatically. In India, for example, the proportion is only 16%. Longer education and training periods and the increasing use of computers also in leisure cause the fact that the eyes simply lose the ability to see at a long distance. But at the same time development brings ever better ways to balance a defective vision (cf. Kuratorium Gutes Sehen, 2011).
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