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Lecture 6


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PSYC 100
Sherri Atwood

1 Sensation and Perception Propagnasia (aka face blindness) – can’t recognise people by their face Sensation – sensory receptors and nervous system receive and represent stimulus energies from our environment • Brain receives input from the sensory organs Perception – organising and interpreting sensory information; enables us to recognise meaningful objects and events – the meaning we give to our sensations • Brain makes sense out of the input from our sensory input Sensation vs Perception – Sensation – detection of environmental stimuli Perception – experience of detecting those stimuli Sense receptors – transform physical energy in the environment/body to electrical energy which is then transmitted to the brain as nerve impulses • Dendrites are responsible for smell, pressure, pain, temperature Doctrine of specific nerve energies – signals received by sense organs stimulate different nerve pathways going to different parts of the brain • Synesthesia – sensory crossover – stimulation of one sense consistently evokes sensation in another Bottom-Up Processing – taking sensory information and then assembling and integrating it. • What am I seeing? Top-Down Processing – using models, ideas, and expectations to interpret sensory information • Is that something I’ve seen before? Sensory signals have to be transformed in order to be understood by the brain – transformed into neural code • Transduction – aka conversion of one energy to another From Sensory Organs to the Brain: 1. Reception – stimulation of sensory receptor cells by energy 2. Transduction – transforming this cell stimulation into neural impulses 3. Transmission – delivering this neural information to brain in order to be processed Psychophysics – field dealing with the relationship between the actual physical properties of stimuli and our experience of these stimuli Absolute Threshold – minimum level of stimulus intensity needed to detect a stimulus half of the time • lower threshold = higher sensitivity Anything below threshold is considered “subliminal” Sensitivity fluctuates – there is no fixed sensitivity point, people set their own standards 2 Sensation and Perception Difference Threshold – minimum difference for a person to be able to detect the difference half of the time Weber’s Law – for 2 stimuli to be perceived as different, they must differ by a constant minimum percentage, not a constant amount Sensory Adaptation – sensory neurons decrease activity when there is a constant stimulus Perceptual Set – what we expect to see, which influences what we do see • This is an example of top-down processing The brain turns waves from electromagnetic radiation into sensation and colours Colour/Hue and Brightness: • Great amplitude (bright colours), Small amplitude (dull colours) • High Frequency (bluish colours), Low Frequency (reddish colours) Lens changes shape to focus on near or far objects Nearsighted – far away objects are focused in front of the retina Farsighted – beyond the retina Blind spot – area of missing information in our field of vision The Retina: 1. Light entering eye triggers photochemical reaction in rods and cones at back of retina 2. Chemical reaction in turn activates bipolar cells 3. Bipolar cells activate ganglion cells, the axons of which converge to form the optic nerve. Transmits information to the visual cortex in the brain Rods help us see black and white actions in our peripheral and in the dark ((NIGHT)) • 20x more common than cones Cones help us see sharp colourful details in bright light ((DAY)) Images are made of neural signals which can be produced even by pressure on the eyeball • Neural signals enter optic nerve, and then are sent through thalamus to visual cortex Objects in left visual field stimulate right have of retina and vice versa Primary colours (RGB) of light all overlap to create WHITE Black surfaces reflect no light – adding RGB paint together creates a blackish colour 3 Sensation and Perception Young-Helmholtz Trichromatic Theory: • Three types of colour receptor cones RGB • Colours we perceive are created by light waves stimulating combinations of these cones Opponent Process Theory – each 3 cone types responds to 2 different wavelengths • RED or GREEN, BLUE or YELLOW, BLACK or WHITE Dual Process Theory – combination of Young-Helmholtz Trichromatic Theory and Opponent Process Theory Fe
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