PSY 102 Lecture Notes - Lecture 5: Mondegreen, Cochlea, Middle Ear
5 Jun 2018
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Lecture 5 October 18, 2017
Sensation and Perception
• Sensation (sensory transduction) – the process of turning physical input (such as
wavelengths of light) into the electro-chemical language of your nervous system.
o Raw stimulus
• Perception – the process of assigning meaning to that stimulation.
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.
Sensations vs. Perceptions
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
processed by the brain.
(3) Outline how a stable, meaningful interpretation of visual information (a
perception) is created and why the interpretation process sometimes leads to
visual illusions.
Translating the input: Visual transduction.
• Visile light fors just oe part of the spetrum of electro-magnetic radiation
(energy)
• Wavelength – the distance from one energy peak to another = colour.
• Intensity – how much energy is transmitted = brightness.
Entering the eye.
• Your retina contains light-sensitive receptor cells (sensory neurons called
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Lecture 5 October 18, 2017
photoreceptors)
• The first job of your eye is to control the amount of light entering the eye and
focus it onto your retina.
o Fovea is a clump of photoreceptors, photoreceptors are spread out
among the other parts 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.
• For near objects, the lens gets shorter and fatter. For far objects, it becomes long
and thin (accommodation).
• The light-sensitive cells in the retina contain photo pigments that react to light,
causing a chemical change in the cell that results in neural activity.
• Red-eye happens when taking photos with direct flash in a dark environment
o Blood at the back of the eye
Receptor cells: Rods and cones.
• Rods:
o 120 million
o Scattered around the edge
o More sensitive than cones
o Night vision
• Cones:
o 6 million
o Central area (fovea)
o Less sensitive than rods
o Require more light to send signals
o Colour vision
o Fine detail
o Can be difficult to figure out what colour something is in the dark
Dark adaptation.
• The process through which you are gradually able to see more and more
effectively in the dark.
Early processing in the retina.
• By oiig the atiity of seeral reeptor ells i its reeptie field, a
ganglion cell can detect simple features of the world (edges).
• 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.
The visual information pathway.
• Information passes through the optic nerve, over the optic chiasm (where signals
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Lecture 5 October 18, 2017
cross between the hemispheres) and to the lateral geniculate nucleus (LGN).
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.
• Prosopagnosic people often use other cues to recognise people, such as:
o Voices & gait
o Clothes
o General body size and shape
• Visual agnosia – the inability to recognise certain classes of objects, often despite
being able to see their shape.
o Akinetopsia – the inability to perceive movement.
• Brain-imaging 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.
• Colour is processed at all stages of visual processing; in the retina (cones), LGN
and visual cortex.
• A red ojet is ot atually red. It reflets a aelegth of eletro-magnetic
radiation that your visual system perceives as red.
• Cone cells are responsible for the perception of colour. There are three different
types of cone cell, one that is maximally responsive to short wavelengths of light
0 ~ lue, oe to ediu 0 ~ gree ad oe to log 0 ~
red.
• Each type of cell has a different type of photopigment.
But, that at e the hole story.
• After-images.
o When you have stared at certain colours for long enough, when they
disappear, an after-image of another colour appears.
Image After-image
Red Green
Blue Yellow
Green Red
Yellow Blue
Opponent processes:
• Neurons can start sending the signals more or less frequently
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Document Summary
Sensation and perception: sensation (sensory transduction) the process of turning physical input (such as wavelengths of light) into the electro-chemical language of your nervous system, raw stimulus, perception the process of assigning meaning to that stimulation. Translating the input: visual transduction. (cid:858)visi(cid:271)le(cid:859) light for(cid:373)s just o(cid:374)e part of the spe(cid:272)trum of electro-magnetic radiation (energy: wavelength the distance from one energy peak to another = colour. Intensity how much energy is transmitted = brightness. Entering the eye: your retina contains light-sensitive receptor cells (sensory neurons called. Dark adaptation: the process through which you are gradually able to see more and more effectively in the dark. Information passes through the optic nerve, over the optic chiasm (where signals. October 18, 2017 cross between the hemispheres) and to the lateral geniculate nucleus (lgn). Processing the visual scene: simple cells can detect lines, by combining the input of simple cells, more elaborate patterns can be detected.
