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P e r c e p t i o n a n d t h e

S e n s e s

I V i s i o n

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A human has over one hundred and twenty million light receptors inside just one eye. These are then funnelled through one million channels in the optic nerve - where electrical pulses are transmitted through the spinal cord and to the brain; this is where the pulses are decoded and re-transmitted as electrical signals sent to different muscles throughout the nervous system. This re-assembly of the electrical signals happens in a fraction of a second. The v isible sp e c t r um is t he portion of the electromagnetic spectrum that is visible to (can be detected by) the human eye. Electromagnetic radiation in this range of wavelengths is called visible light and it is this and only this which a person can see. Light particles called photons are transmitted to the eye and picked up by specialised receptor cells in the retina.

Different visual cues are picked up on in different parts of the brain - there are different sections of neurons for : or ient at ion, proximity, time and space. These parts of the brain work together to detect coincidence and formulate correspondence between all the visual data we receive. It is these coincidences w hich we t hen remember at a later date when put in a similar situation; the brain

formulates a kind of predictive hypothesis, an internal reality which decodes what we see into a scene which is easy for us to understand. For example, when we see two points forming a right angle, we automatically assume that the two loose end points will connect to form a right angled triangle, as we have seen a triangle more times in our lives that just two lines.

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wavelength in centimetres

Visible light bounces of the object in our field of vision, through the cornea where the rays of light are bent so they can be directed through the lens of the eye. Once the light rays are bent they are then focused onto the retina. The retina is actually part of the brain that is isolated to serve as a transducer (a device that converts one form of energy to another ) for the conversion of patterns of light into neuronal signals.

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a) rays of light from object b) cornea c) lens d) light rays focus on retina e) optic nerve f) gamma ray g) x-ray h) ultraviolet ray i) visible spectrum of light j) infrared wave k) microve l) radio wave

Because if the internal hypothesis we c re ate, t he br ai n a d opt s strategies for making the most of limited information - in essence perception departs from physics. The image on this page clearly looks like a leaf, however, in reality a large proportion of the leaf is gone. The brain picks up on this distortion and revisits it’s internal catalogue of everything it has seen before. The greater part of the image resembles an ivy leaf, despite about thirty percent of it being made up of out of place ambiguous shapes (what we know in our mind to be holes where leaf used to be,

but our mind needs to process the ambiguous image). The brain will automatically screen out what it perceives as not to be relevant (ambiguous shapes) and focus in on what is relevant; this is what we now call an attentional spotlight. Mechanisms in the brain facilitate enhancing or impairing what we are seeing according to a group of neurons which detect relevance. They are able to suppress and inhibit what we think we see. Another way to explain this would be referring to how a child draws a face. It is universally known that

the symbols used when drawing a face are two dots (eyes) a vertical line (nose) and a curved horizontal line (the mouth). These mishmash of symbols in reality are barely like a face at all - but the brain builds on what is there on the paper, by referring back to previous experiences, building a hypothesis and then constructing the image into what we know to be a face.

“Ambiguity or lack of information about a target leads to a greater need for interpretation and addition.� -Alan Saks

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Hearing (or audition) is the ability to perceive sound by detecting vibrations. The auditory system includes the ears and inner structures which produce signals in response to the sound waves in the air. Hearing involves the complex task of separating out the sources of interest, often estimating their distance and direction as well as identifying them. Opposed to the sense of vision where the body reacts to photons, when looking at how sound is perceived we see how the ear reacts to tiny mechanical changes in the air, and how they are passed through the inner of the ear where the vibrations are transmitted, amplified and broken up into different frequencies. T h e re are ove r on e m i l l i on mechanisms in the cochlea: each denotes a different frequency.

The sound is passed though the auditory nerve where the sound is filtered through synapses via electrical impulses. Sound and vision always work together. Humans are born with the innate ability to localise sound - sound is pin-pointed (localised) when it is paired with vision, this is the reason why babies are always drawn the loudest sound. Auditory and visual cues also work

together to help us understand language; many syllables have auditory similars - for example the sounds: ‘bah’, ‘gah’ and ‘dah’ all sound the same to a person who is blindfolded. It is necessary for the visual sense to work with audition for the brain to decode dynamic sounds. In relation to this, lip reading similarly fills in missing auditory signals. Vague or ambiguous sounds are decoded by the brain

once they are paired with a visual cue which the mind knows (from experience) consequents in a particular sound. This is how people who become deaf still have the ability to understand what people are saying by paying close attention to the ways their lips move.

Vibrations in the air (sound waves) are funnelled through the outer ear and inside the ear canal where they reach the ear drum. And, like a drum, this amplifies and intensifies the vibrations which are then transmitted through the cochlea. The cochlea is filled with a fluid like membrane where vibrations are then separated into different frequencies and transferred through tiny hairs and then passed to the auditory nerve and transmitted via nerve impulses to different parts of the brain where they can separately be reassembled into a symphony of sounds.

a) ear canal b) ear drum c) auditory nerve (to the brain) d) cochlea e) sound waves given off by a crisp autumnal leaf

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“Touch comes before sight, before speech. It is the first language and the last, and it always tells the truth.� -Margaret Atwood, The Blind Assassin Touch or somatosensory, is also called tactition or mechanoreception. It is a perception resulting from activation of neural receptors, generally in the skin including hair follicles, but also in the tongue and throat.

A variety of pressure receptors respond to variations in pressure (firm, brushing, sustained, etc.). The touch sense of itching caused by insect bites or allergies involves special itch-specific neurons in the skin and spinal cord. The loss or impairment of the ability to feel anything touched is called tactile anaesthesia. Paraesthesia is a sensation of tingling, pricking, or numbness of the skin that may result from nerve damage and may be permanent or temporary. The senses of touch and sight are very closely interlinked; as soon as a person is born, they begin

carrying out experiments to find correlations between the senses. Seeing an object visually and then exploring its’ tactile qualities creates a predetermined hypothesis in our mind (by our brain decoding these multiple sensory queues) so the next time we come into contact with it, or something which seems similar to it, it seems familiar to us - we learn from our previous explorations and experiences.

a) hair b) skin epidermis c) hair follicle d) artary e) hair root The hair is disturbed, this movement is passed through the hair down to the hair follicle, the hair root is surrounded by sensory cells which send signals via synaptic receptors up the spinal cord to the brain.

N o c i c e p t i o n No c i c e pt i on is t he s e ns e of physiological pain. Specialised nociception pain receptors signal ner ve-damage or damaged tissues. There are three types of pain receptors: cutaneous (skin), somatic (joints and bones), and visceral (body organs); information is carried via these receptors to a specific area of the brain which motivates us to avoid pain, the anterior cingulate gyrus.

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Olfaction or olfactory perception is the sense of smell. This sense is mediated by specialized sensory cells of the nasal cavity. The olfactory system works based on tiny chemical signals in the air called odourants.


The odour from the f lower in detected by a sensory cell in the nose. The cell is specialised in such a way that it has cilia on the end of it - hair like structures to increase the surface area of the cell where the smell can be detected. This increases the chance of a person smelling more faint smells. The cilia send an electric pulse through the smell receptor, which in turn signals the release of chemicals which travels though a synaptic gap and then quickly through the olfactory nerve to the brain. Different odours trigger different amounts of a chemical to be released in the brain.

The chemicals are recognised by the brain, all of the signals sent from the sensory receptor are collected and then reassembled by the brain, to deduce what kind of smell has been detected. However strong or weak a smell is, also allows it to be visually localised by the brain. This allows the senses to come together and create a unified perception of the world around them.

a) cilia b) smell receptor c) olfactory epithelium d) olfactory nerve to the brain e) odour from flower f) cell nucleus

V T a s t e

The tongue is filled with hundreds of thousands of minute, specialised neurons which detect different flavours. Interestingly, the neurons also play a large part a human’s sense of smell - people can in fact taste very strong odours. The sense of taste is the only chemical sense, reactions are constantly happening in our mouths. When something is placed on the tongue and upsets the homeostasis of the mouth, signals are sent to the brain which indicate taste. Signals from our taste buds are sent from our tongue to the brain. The brain never tastes what we have inside our mouth - however, it works hard to decode the sensory messages which are sent to it. For example, a person will bite into a strawberry and the juices will react to the part of the tongue which detects ‘sweet’ tastes. The brain will release chemicals which give out feelings of satisfaction.

Here, a person will have learned an association; red fruit make us feel satisfied when we eat them. It is said that we are born with an innate catalogue of already learned taste and visual associations which would have been learnt by our ancestors and then carried down throughout generations carried by specialised DNA. This can be seen when babies show a natural disliking to green or

blue foods, as these colours are naturally associated with the taste of mould. On the other hand, experiments have shown that babies are predisposed to enjoy red and orange foods - colours which for years have been associated with the sweet, sugary taste of ripe fruits. However, in recent culture natural foods are becoming less and less frequently eaten; and more






processed foods are being chosen as an a lter nat ive. Pro cess e d foods rarely look like the natural foods which they are derived from; and the innate associations which humans are born with are becoming confused. One thousand years ago, sight and smell would be the senses which would be relied upon to make sure food was edible; now taste and the visual senses do not work so much in harmony as more processed foods do not in keep with our innate learned associations, as the visual cues are not associated with traditional, set tastes.

One can see here that the senses of a human are evolving; however we are retaining other innate forms of information. A caveman would be driven to find rich, fatty foods in order for him to be sustained when conditions were seen as too hard to hunt, scientists say that we never lost this innate drive to eat fatty foods and prize them over other sustenance; as fatty food is becoming more readily available, humans find it hard to refuse it because of their deep set cave-man instinct.

a) human tongue b) bitter taste receptors c) sour taste receptors d) sweet taste receptors

I n f o r m a t i o n & i m a g e s a s s e m b l e d b y L u c y R o s s e l l E v a n s


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