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psyc lecture, sensation and preception .docx

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Department
Psychology
Course
PSY 102
Professor
Stephen Want
Semester
Winter

Description
lPsy102: Introduction to Psychology (4) Sensation and Perception Stephen Want Sensation and Perception  Sensation – the process of turning physical input (such as wavelengths of light) into the electro-chemical language of your nervous system.  Perception – the process of assigning meaning to that stimulation. First step in sensation is when external energy or substance gets converted into excitation or inhibition, called transduction. Is it a duck (looking to the left), or a rabbit (looking to the right)? * The various lines, angles and shades of grey in this image provide you with many visual sensations. * These sensations do not differ when you see the rabbit from when you see the duck. Instead, your perception changes. Our brain is interpreting the sensations differently, creating different perspectives Gustav Fechner, published a landmark piece on perception. The field psychophysics evolved out of his work, how we perceive sensory stimuli based on their physical characteristics. Colour of light is called hue by psychologists We’re sensitive to 3 colours, red green and blue. Mixing of these colours called additive colour mixing can create any colour. Mixing equal amounts of red, green and blue light produces white light. Mixing of coloured pigments in paint of ink is called subtracting colour mixing. Vision: Creating a world of meaningful objects. (1) Describe how light gets translated into the electrochemical language of the brain. (2) Explain how the essential features of the visual input, such as colour, are extracted by the brain. (3) Outline how a stable, meaningful interpretation of visual information is created and why the interpretation process sometimes leads to visual illusions. Translating the input: Visual transduction. * ‘Visible’ light forms just one part of the spectrum of electro- magnetic radiation. Wavelength – the distance from one energy peak to another = colour/hue. Intensity – how much energy is transmitted = brightness. Gamma rays, x-rays, ultraviolet, infrared, radio waves Red – high wavelength, Violet- small wavelength Entering the eye. Sclera, is the white of the eye an lipochrome for yellowish-brown.ye, pigments cause eye colour, melanin for brown  Your retina, thin membrane at the back of the eye, contains light-sensitive receptor cells. Fovea is the central part of retina responsible for acuity, sharpness of vision. Light enters through pupil, which can control the amount of light streaming in to the eye by blinking or the ‘pupilary reflex’. Dilation is called the expansion of the pupil Cornea, layer that covers the iris and pupil, bends incoming glight to focus it on back of the eye. Lens bends light, cells of light are transparent allowing light to pass through. * The first job of your eye is to focus the incoming light onto your retina. Fovea, Optic nerve Front part- controls the amount of light that comes in the eye. Back part- reflects or turns the image your seeing Red eye- reason, because your seeing the persons retina, retina is red. Because its dark, pupil is wide open. Accommodation: lense changes shape to focus light on back of the eye.  Light has to be focussed on your retina by the lens, which changes shape depending on whether you are looking at an object that is close to you or far away. Muscles are adjusting the shape of the lens.  For near objects called myopia, the cornea being too steep or our eyes too long.  For far objects called hyperopia, the cornea is too flat ou our eyes too short.  The light-sensitive cells in the retina contain photopigments that react to light, causing a chemical change in the cell that results in neural activity. Chemical breakdown in the sensory neurons  Eyeball loses flexibility when we get old—poorer vision. Receptor cells: Rods and cones. Receptor cells located in outermost layer * Rods: at night light falls on rod cells, do not perform colour , don’t pick up colour. * 120 million * Edge rather than centre of retina * More sensitive than cones * Night vision Rods: long and narrow, enable us to see basic shapes and forms., low level light Photopigment in rods is rhodopsin, vitamin A is needed to make rhodopsin. After staring at an image for a while and then looking at a white wall, you see a reverse image because sense receptors become fatigued after too much photopigment is bleached. Photopigment is bleached when light enters the rods.  Cones: Cones: shaped like small cones, colour vision, sensitive to detail, require more light than rodes do.  6 million  Central  Less sensitive than rods  Colour vision advantage over rod cells  Fine detail “ Dark adaptation. * The process through which you are gradually able to see more and more effectively in the dark. Eye starts to get full of photo pigment. Gradually chemical gets replenished. Eyes full with photo pigment have maximum sensitivity. Adaptation to the dark, eyes are full of photo pigment. Cover one eye in the dark, then eyes adapt to the dark easier. Just like pirates, sea is bright and inside of the ship is dark. Early processing in the retina. * By combining the activity of several receptor cells in its ‘receptive field’, a ganglion cell can detect simple features of the array. Ganglion cells contain axons, bundle axons together and depart the eye to reach the brain. Ganglion cell sends on signal (positive), bipolar cells (positive and negative) send on signal to the rods. 3 positive rods for a positive bipolar cell and 3 negative rods for a negative bipolar cell.  At the point where the optic nerve, which carries visual information to the brain, leaves the eyeball, there is a blind spot where no receptor cells are located. Blind spots result, because axons of ganglion cells push everything else aside.Point in our vision where were blind, no receptor cells (rods and cones), nothing there to detect it. Optic nerve contains axons of ganglion cells, takes all the messages from the retina into the brain. Fork on the way is called optic chiasm, half axons cross optic chiasm and other half stay on the same side. Optic nerves turn into optic tracts, which send axons to visual thalamus and then to primary visual cortex. Remaining axons go to superior colliculus in the midbrain, the temporal lobe for visual form and colour and the parietal lobe for visual form, position and motion. Strange- you don’t experience it. Brain takes a guess on what is there and finds image that’s a demonstration of the blind spot. The visual information pathway. * Information passes through the optic nerve, over the optic chiasm (where signals cross between the hemispheres) and to the lateral geniculate nucleus (LGN). Left side of space hits the right side of the retina. And the other way around. Processing the visual scene. * Simple cells can detect lines. * By combining the input of simple cells, more elaborate patterns can be detected. Brain damage and the visual system. * Prosopagnosia – the inability to process faces. Visual impairment, people can’t recognize faces. Prosopagnosic people often use other cues to recognise people, such as: * Voices & gait * Clothes * General body size and shape * Visual agnosia – the inability to recognise certain classes of objects, often despite being able to see their form. Able to tell us the shape and colour of an object but cant recognize i * Akinetopsia – the inability to perceive movement. Jumps no smooth movement, people with this condition tend to find it difficult to interact with people, can’t perceive their movements. * PET studies demonstrate which areas of the brain are most active when we process visual stimuli. They show that different parts of our brains process different information from the visual field. Colour vision: Trichromatic theory. We bas
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