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Lecture

PSY100 may 16
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Department
Psychology
Course
PSY201H5
Professor
Bruce Schneider
Semester
Summer

Description
PSY100 May 16 th Thresholds - sensory receptors are tuned to a particular form of energy o auditory receptors in the ear code for sound pressure changes, but not for light - sensory systems require a minimum amount of energy for activation (absolute threshold) o JND: the minimum difference in stimulation that is just noticeable  Weber notices that the JND is a fraction of the original stimulus intensity – the fraction is different for different senses The Visual System - the eye detects electromagnetic radiation (light) o vision is functional  allows for detection of movement (predator or prey)  allows for detection of colour (ripe or spoiled) - light detection is useful because: o light travels rapidly (no delay, unlike hearing) o light travels in straight lines (no distortion) o light interacts with the surfaces of objects in the environment (is reflected or absorbed) o more parts dedicated to vision in the brain than any other function - electromagnetic spectrum Details of the Human Eye - cornea: protects the aqeous humour – keeps oxygenation – protecting the outer layer of the eye - iris: colour band of muscle – bends and contracts to allow light to hit the lens at different angles - fovea: central spot of the retina - retina: begin to process light – full of rods and cones – responds to different wavelengths of light (colour) - rods: visual receptor cells - lens: round, shaped like a ball cut in half – astigmatism (lens are not round) - optic nerve: bundle of axons – horizontal, bipoliar, ganglian cells (about a million) that are connected to a billion axons that are bundled together – (blind spot) : one eye is always compensating for the other Transduction of Light - light travels thought the retina to impinge on photoreceptors at the back of the eye o light bleaches a pigment contained within the photoreceptors  bleaching leads to a graded receptor potential (summation of amount of energy) that eventually produces an action potential in the ganglion cell  if it reaches the threshold, it sends the impulse  produces an AP in the ganglion cell if there is enough stimulation for the graded potential to reach threshold - two types of photoreceptors o cones: found in the center of retina (fovea) and are sensitive to fine detail and colour – 67 million cones ~ different wavelengths of light o rods: found in the periphery of retina and are sensitive to movement but not fine detail – good for night vision – 125 million rods in each eye Perception of Colour - colour is a psychological perception - three dimensions of colour: o hue is the apparent colour of an object (blue) o brightness is the intensity of a colour o saturation is the purity of the colour - three different types of cones are found in the eye o each is sensitive to different wavelengths of light  S-cones: blue - BIV  M-cones: green – B goes to G and Y  L-cones: red – RO - tri-chromatic colour theory o problems: complementary colours (opposite colours in the colour wheel) o di-chromatic colour blindness – RG or BY (less common)  women have less colour blindness because of evolutionary adaptation – women were the gatherers – they needed to know which berries were not poisonous o after-images: negative colour after-images and di-chromatic colour blindess – got in the way of tri-chromatic colour blindness  excess energy due to the over stimulation – aren’t going to fire anymore (refractory phase) but the neurons that were inhibited by green and were staring at red, take over some of the spill- over energy so when you close your eyes, you see the same image, but in the colours of the inhibitors – residual energy stimulating previously inhibited neurons - colour starts with the tri-chromatic theory at the retina, but then Hering’s opponent process theory takes over – Thalamus and visual cortex (occipital lobe) Colour Vision Theories - colour is explained Visual Pathways in Brain, “Where” vs “What” - brain is contra-laterally connected - either eye has connections to both hemispheres to the brain o but there are certain things that if only one eye sees something, it will send the information only to
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