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Psychology. BHP315111. MODULE 4 Psychobiological Processes - SENSATION. 2 principles…. Sensations versus perceptions : Gathering information takes 2 steps. Firstly, electrical signals reach the brain. Secondly, they are then changed into sensations.
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Psychology BHP315111
2 principles… • Sensations versus perceptions: Gathering information takes 2 steps. Firstly, electrical signals reach the brain. Secondly, they are then changed into sensations. • Sensations: meaningless bits of information that come from electrical signals from the sense organs. • The brain quickly changes sensations into perceptions. Perceptions are meaningful sensory experiences that happen after the brain combines hundreds of sensations.
2 principles… • Transduction: Molecules enter your sense organ (e.g. nose, eyes, hands, ears, mouth), which transforms the molecules into electrical signals, that are interpreted by your brain as pleasant or unpleasant signals. • When you go passed the abattoir, molecules are sent to your nose, where the brain transforms them to electrical signals, that tell you that it stinks!
2 principles… • Sensory Adaptation: This refers to the decreasing response of the sense organs, the more they are exposed to a continuous stimulation. • Jewellery, Glasses • Noise in a Club or cafe • Clothes on your skin • Cadbury factory • Intense stimulation (very hot shower) may cause pain, which warns us of further injury.
Absolute threshold • Even if a sensory system has the capacity to respond to a stimulus, the individual may not experience the stimulus if its too weak. • The minimum amount of physical energy needed for an observer to notice a stimulus is called an absolute threshold. • With sound, psychologists could play sounds of a particular pitch and volume, and see if subjects could hear it. Some sounds would be so soft we wouldn’t hear!
Absolute thresholds • Brown, Galanter, Hess & Mandler, 1962 came up with the following absolute thresholds: • Hearing: the ticking of a watch six metres away in a quiet place • Smell: one drop of perfume in a large house • Taste: one teaspoon of sugar dissolved in 10 litres of water • Touch: the wing of a fly falling on the cheek from a height of one centimetre • Vision: The flame of a candle 50 kilometres away on a dark, clear night.
Absolute thresholds • Despite this, however, absolute thresholds vary from person to person and situation to situation. • Sometimes noise can affect our performance. External noise can affect us, as well as internal noise, such as the random firing of neurons. Stress, motivation, expectations and fatigue can also hinder results. • Someone who has been burgled, for example, is more likely to ‘hear’ suspicious noises, whether they occur or not.
Difference threshold • Difference threshold is the lowest level of stimulation required to sense that a change in stimulation has occurred. • If two light bulbs are in a room and have a different wattage can you tell? There needs to be a just noticeable difference (jnd). The jnd depends on the intensity of the new stimulus and the level of stimulation in the one already present.
JND • The more intense the existing stimulus, the larger the change must be to be noticeable. • A person carrying a 1kg backpack will notice the addition of a 500 gram book into it. • A person carrying a 30kg backpack will hardly notice the addition of a 500 gram book, and won’t think the pack feels any heavier. • This has therefore not produced a JND.
Light! • Light is so important when it comes to your eyes! It can be useful for: • Tracking prey • Avoiding predators • Checking out potential mates • There are some forms of energy, however, that we can’t see. The receptors in the human eye are tuned to detect only a very restricted portion of the electromagnetic spectrum, from 400 to 700 nanometres (nm).
Electromagnetic Spectrum • We only see a small part of the spectrum, the visible light waves. • Other organisms are sensitive to different regions of the spectrum. • Many insects (ants and bees) and some vertebrate animals (iguanas and some birds species) can see ultraviolet light.
Light facts… • Light travels very quickly (300,000 kilometres per second) so we can see thing almost immediately after they happen. • Light travels in straight lines, which means that it preserves the geometric organisation (shape) of the object it illuminates • Light interacts with molecules on the surface and either absorbs or reflects it.
The eye • The cornea, pupil and lens focus light on the retina. • The retina transduces this visual image into impulses that are relayed and interpreted by the brain. • Choose an area to study in depth, creating a PowerPoint slide on what its role is, using diagrams and text. • Cornea, Pupil, Iris, Lens.
Seven steps • For you to see a 16 foot tall giraffe, your eyes perform 7 steps. • Image reversed • Light waves • Cornea • Pupil • Iris • Lens • Retina
Image reversed • Have a look at pg 94 of your textbook • The giraffe appears upside down at the back of the eye. What the eye does, is focuses on the giraffe, and then the brain turns the upside down giraffe right side up. Thus, the image is reversed.
Light waves • When we view an object, the light waves are viewed in a broad beam, such as a spread beam driving light. In order to see object clearly, your eyes must change the broad beam light waves into narrow, focused waves, like a pencil beam light.
The Cornea • The cornea is a transparent rounded cover that is positioned over the eye. • The job of the cornea is to focus the light coming in, into a narrower beam of light. The cornea has two layers which help it refract the light into a more narrow beam. The cornea accounts for 2 thirds of your optical power and is only half a millimetre thick. • The cornea will become cloudy and hazy if the eye is removed or they person dies.
The Pupil • The Pupil serves two main functions. • The first purpose of the pupil is to control or regulate the amount of light that is coming in to the retina. • It does this by contracting (making the pupil smaller) and dilating (making the pupil larger).The pupil will dilate in low light and contract in bright light in order to adapt and provide the clearest image possible • The pupil also improves the optical quality of the image on the retina and provides a sharper image by helping to stabilise the eye.
The iris is the opening of the pupil. It is a circular muscle that surrounds the pupil and it is in control of how much light enters the eye. When it is darker the iris relaxes more and allows more light to enter the eye allowing the pupil to dilate. In bright light the iris Iris Anatomy constricts allowing less light to enter the eye which also constricts your pupil. The iris gets it colour from the pigment of the muscle.
The Eyes Lens The lens is transparent with an oval shape that is attached to the eye by muscles. The lens is located right behind the iris (coloured bit). The lens is what allows us to see distance in terms of how far away something is. For far away objects light waves need less bending (focusing), so muscles automatically stretch the lens so that its surface is less curved. For near objects lights waves need more bending (focusing). The lens of your eye focuses and refracts light so that it will appear on your retina. The retina are nerves that send messages to your brain; to tell what you are seeing. The lens works much like the lens of a movie projector at the movies. It is what focuses your images.
Retina • The eye is like a camera, in that is has: • An opening to adjust the amount of incoming light • A lens to focus the light • The equivalent of a film; the retina. • It is not like camera, in the sense that it works best when it is moving.
Retina • The retina is located at the back of the eye. It contains cells that are extremely sensitive to light. These cells are called photoreceptors. They absorb the light waves and start the process of transduction. • They are called photoreceptors, because the greek word for ‘light’ is ‘photo’. • They are called rods and cones because of their distinctive shape.
Retina • Each retina contains around 120 million rods and 8 million cones. When a rod or a cone absorbs light energy, it makes an electrical signal which stimulates the bipolar cells. • The bipolar cells are each responsible for a bit of information about what has been seen. The ganglion cells integrate information from all the bipolar cells and send the information to the optic nerve. • The ganglion cells bundle together to form the optic nerve. This nerve carries all the visual information to the brain.
Retina • The fovea is at the central part of the retina and this is most sensitive to small detail, so vision is sharpest for things directly in sight. • The blind spot, however, is where the optic nerve leaves the eye, so it has no receptor cells.
The Blind Spot Close your left eye, fix you gaze on the plus, and slowly move towards the picture. The circle will disappear when it fall in the blind spot of the right retina.
Blind Spot • Most people are unaware of their blind spot because of the following reasons: • One eye sees what the other does not • The eyes are always moving, providing information about the missing area. • The brain uses information from the rest of the retina to fill the gap, so there is no empty visual space.
The eye so far… • Light is focused on the retina by the cornea, pupil and lens • The retina transduces this visual image into a code that the brain can read (data reduction system) • The photoreceptors, rods (black, white and grey) and cones (colour), excite bipolar cells, which in turn excite or inhibit ganglion cells. • The ganglion cells make up the optic nerve.
What happens now? • Once the optic nerve receives information from the retina, it then carries it to the optic chiasm, where the optic nerve splits. It then crosses over (information from the right visual field goes to the left hemisphere and vice versa). • Eventually the information gets to the optic tract, which carries the information to the primary visual cortex.
Primary visual cortex • Once the information reaches the Primary visual cortex, the first point of call is the striate cortex. It’s the ‘first stop’ for all visual information. • Neurons here begin to make sense of visual information, through action neurons called feature detectors. • They are neurons that only fire when stimulation in their field matches a very specific pattern.
What pathway • The what pathway runs from the striate cortex in the occipital lobes through the lower part of the temporal lobes. • It determines what an object is. Lines are integrated into more complex combinations (like cones or squares). • At other locations along the pathway, the brain processes features of the object like colour and texture.
Where pathway • The where pathway is interested in locating the object in space, following its movement and guiding movement toward it. It runs from the striate cortex through the middle and upper regions of the temporal lobes. • Prosopagnosia (unable to recognise colours or familiar faces) have lesions at various points along the ‘what’ pathway. Patients that have lesions along the ‘where’ pathway, may be able to name objects, but might bump into things or have trouble grasping things.
The end result! • Information from other senses also come in contact with visual information. E.g. – when you shake hands with someone, you not only see the other person’s hand, but you also feel it, hear them walk toward you and feel your own arm moving through space. • Once the information has reached the front section of the temporal lobes, it fully integrates a perception, but not until then!
Colour! • What colour is the heading? Is it blue? Purple? • Colour is a psychological property, not a quality of the stimulus. It is something we perceive. • Grass is not green to a cow because cows lack colour receptors. Insects, reptiles, fish and birds, however, have excellent colour vision. • Colours are colours because they absorb certain wavelengths and reflect others.
Colour! • Colours actually have three psychological dimensions: hue, saturation and lightness. • Hue is what people commonly mean by colour: whether it appears blue, red, green, etc. • Saturation is a colour’s purity: the extent to which it is diluted with white or black (saturated in its own wavelength) • Lightness is the extent to which a colour is light or dark. • Colour also appears to be related to gender in the West. Which men know what hue bone, magenta, and fuschia are? Cultures seem to vary widely in what they label their colours, but they recognise the same hues.
