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Chapter 5 Sensation and Perception.docx

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University of Calgary
PSYC 200
Michael Boyes

CHAPTER 5: Sensation and Perception Intro • Sensation – lower end, automatically wired in processes o Physical structures of the eye – transduce/convert incoming visual light information into neural impulses • Perception – higher order process o Meaning that we apply to things • E.g. recognition of faces – two-phase process o Sensation o Perception – recognizing, memories • Ongoing debate – where one begins and other ends o Sensation and perception can be thought of as a continuum • Why do we see things automatically? • Illusions? – seeing is believing o By making the process more problematic, we can understand sensation and perception • Picture of a • Monocular cue – something in • M. C. Escher Dalmatian dog – the picture that could be • Trick: decide where it changes, pop-up effect captured in a flat image, no which depends on where it starts • Figure ground depth • Play with 2 dimensions in a way issue (Gestalt) – • All perceptions of depth are we can’t in the real world figure and illusory background • Chalk artist • • Only works if seeing it in two dimensions (in a photo) • Vancouver – decal of a little girl on the road to slow drivers down • Parallel lines converge in the distance – linear perspective – suggest depth • How do we judge distance? 1 Ames Room Zimbardo • Can only look into room with one eye • Look with two eyes – binocular cues of depth and distance  allows you to realize • Woman in • Woman • Distorted room – no right • How many legs? background is appears small angles anywhere regular-sized • Ceiling slopes down, floor slopes up; windows parallel to roof and floor lines • Misperceiving size • Brain has preconceived notions of room to be rectangular • Only works when viewing it two-dimensionally • Illusions tell us how our • Sensation: light hits • Impossible to see both at the perception works receptors  fire  same time stimulates/inhibits other • Both dots in middle the same • Perceptual processes are size neurons theory-driven – know what • Context effect – mitigated • Perception we’re look for by what they’re surrounded • Contrast effect • Prime people to see one or by the other Sensation and Perception • Sensation = process of detecting and encoding stimulus energy in the world o Sensory processes – automatic o Limits – how sensitive are human eyes in general?  Glasses • Perception = organizing and interpreting, finding meaning in what we perceive o Deciding whether it’s a rabbit or a duck o Applying meaning 2 • Attention – affected by: o Stimulus characteristics  E.g. red lights draw attention o Personal factors – individual variability  Personal vigilance – things you’re particularly looking for • E.g. scanning a sea of faces  Perceptual defense – people can cause themselves not to see things that would cause them discomfort (Freud) • Cat grasp syndrome – believe people close to them are imposters • Study – words up on screen, varied time o Most people recognized a word if up for 1/3 to ½ of a second o Took people longer to recognize swear words – longer recognition latency  Made non-noxious word reappear during training phase – e.g. “book”, would give people shocks if word appeared  Typical testing session – latency for recognizing “book” became longer • Open to manipulation Sensation • Psychophysics o Study the relationship between stimuli and our psychological response to them o Absolute bottom end o E.g. How sensitive are people’s ears?  In general  How good can they get?  Range, individual variation  Impacts • Sensory receptors o Detect (process) stimuli and convert energy into neural impulses o Receptors are designed to serve very specific functions Thresholds and Stimulus Change • Thresholds o There is a minimum amount of any given sensation that has to be present or us to notice it o Absolute threshold  Minimum amount of a stimulus that is necessary for us to notice it 50% of the time  Varies depending on which sense is being studied  Headphones  people asked to push “yes” or “no” button in response to sounds, done in sound chamber  Must be present in ideal conditions  Galanter – said that absolute threshold of a sound is the same as a watch ticking in a living room • Vision – ability to see the flame of a single candle at 30km in complete darkness • Touch – wing of a bee dropped on cheek (many sense receptors) from 1 cm • Taste – single cube of sugar in 3 gallons of water • Smell – drop of perfume in a 3-bedroom apartment • Sensory adaptation 3 o If a stimulus is unchanging we become desensitized to it o Keeps us focused on changes, not constants o Visual lab  Head in vice, chemicals in face to immobilize eyes  Light shone so that only one set of receptor cells activated  30 seconds, light seems to disappear due to fatigue of receptor cells o Change gives continuity of perception 10/23/13 – Intro • Sensation/perception continuum • Expectations affect perception • “Ideal conditions” – thresholds Just Noticeable Difference • JND • E.g. one quarter placed in one shoe, two quarters in other shoe – not detectable • Minimum 50% accuracy • Smallest difference in amount of stimulation that a specific sense can detect • Weber’s law o The size of the JND is a constant proportion of the initial stimulus o Graded function – more weight in hand, bigger the weight should be to notice difference  Quarter experiment o E.g. each click to change volume on expensive amplifiers for older stereos sounds different Vision • Control sensory levels to understand perception when conducting research • Electromagnetic energy o Long wavelengths – AC circuits, radio waves, infrared rays o Short wavelengths – visible light, X-rays, UV and gamma rays • Other animals can see other segments of the spectrum of electromagnetic energy o Bees – UV rays and blue-violet, not red o Pit vipers – infrared rays  See heat in the dark o Dogs – can’t see all the colours that human can (no red)  See red with less vividness Our Visible Spectrum • ROYGBIV • Hue determines colour o Depends on length of the distance from one peak to the next on the wave o Wave theory of light instead of particle theory of light • Intensity determines brightness o Depends on amplitude of the wave • Transduction o The process where the eye converts electromagnetic energy (light) into nerve impulses 4 The Eye Parts of the Eye • Cornea o Light initially focused by this transparent covering over the eye • Pupil o Light enters the eye through this opening o Adjust size in light/dark • Iris o Muscle connected to the pupil that changes its size to let in more or less light o Everyone has a unique iris – new security technique being employed by some organizations • Lens o Focus images on fovea o Flexibility of lens changes developmentally  Lens stiffens up with age  Near-point distance – how close you can get something in front of your eyes without it being blurry o Ciliary muscles contract lens for focus o Yellows with age  Perception of colours that involve yellow changes (e.g. green) o Flexible disk under the cornea  Focuses light onto the back of the eye o Accommodation – focusing process  Flexibility of the lens allows eye muscles to adjust light from objects at various distances away • Retina o Light reflected from the lens is received by this sheet of tissue at the back of the eye o Contains the receptors that convert light to nerve impulses o Fovea – densest pack of cone cells  Periphery – more rod cells than cone cells  Rods distributed throughout retina, cones focused on fovea How we see colour: Cones 5 • Retinal cells that respond to particular wavelengths of light, allowing us to see color • Most of our cones are located on the fovea – sharpest resolution of visual stimuli • 3 types of cones, each sensitive to different light frequencies How we see in the dark: Rods • Retinal cells that are very sensitive to light but only register shades of gray (i.e. no colour) • Rods are located everywhere in the retina except in the fovea • Rods allow us to see at night without strong light – this is why we see less color at night o Because of where the rods are on the retina, we see best at night without light in the periphery of our vision • Sense movement • Peripheral vision o Varies for each individual • Dark adaptation o Dark adaptation curve – 20 minutes to get 90% of optimal night vision; 1 hour to get optimal night vision o Fighter pilots WWII – Battle of Britain  Fighter pilots had to sit in the dark to fully dark adapt their eyes to watch for night bombings • Rod cells completely non-responsive to red light – doesn’t affect night adaptation at all Optic Nerve • From the receptor cells in the retina, the converted impulse from light is directed to the optic nerve o This is the large bundle of nerve fibers that carry impulses from the retina to the brain o It sits on the retina but contains no cones or rods, so this is where you experience a ‘blind spot’  We aren’t aware that we have a blind spot: • Brain completes patterns that fall across our blind spot • Eyes are constantly moving (‘filling’ it in) Processing of Visual Information • Retina o Processes electrical impulses, starts to encode and analyze sensory information (at the most basic level) • Optic Nerve o Neurons pick up the messages from retina, transmit to the thalamus, then on to the visual cortex, then on to more specified areas How we see color • Trichromatic theory o 3 types of sensors – 3 types of cone cells  Red, blue & green receptors  Receptors fire in response to colours  Mixes of colours – midlevel firing of multiple receptors o Herring – proposed that specialized receptors respond to wavelengths of certain colours o Can record electrical activity of individual cells 6 • Trichromatic theory doesn’t explain after-image effects • Opponent-process theory o Baseline firing rate  Identify stimuli by observing rate of firing – excites/inhibits pairs of colours o Receptors respond to pairs of colors  White-black / red-green / yellow-blue o Opponent process cells don’t exist in retina, but exist higher up in visual system • Which is correct? o Both! Pa
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