Unit VI: Perception: Perceptual constancy Stimuli changes, object perceived to stay the same In other words: Image on retina changes, but brain perceives image as being constant/unchanging Stimuli changes, but percept remains the same Sensation changes, perception doesn’t

Unit VI: Perception: Perceptual constancy Changes include: Shape Size Level of illumination (light) Color Distance

Unit VI: Perception: Perceptual constancy Shape constancy For familiar object; image on retina changes, still perceive it as original shape Image on retina changes because object moved in some way

Unit VI: Perception: Perceptual constancy Size constancy Objects perceived as having constant size, even when distance varies Size constancy: the brain perceives the two people as being the same size, because they’re both people.

Unit VI: Perception: Perceptual constancy Lightness/brightness constancy Object perceives to have constant color even when illumination varies Relative luminance: Amount of light an object reflects relative to its surrounding

Unit VI: Perception: Perceptual constancy Lightness/brightness constancy Example Black and white sheets of paper in normal light Looks black and white Black and white sheets of paper in high light Both still appear black and white Both are reflecting back more light than previously

Unit V: Sensation – Color vision Color vision – theories Color constancy How we see color is influenced by its surroundings & context Put object into different surrounding, color may appear different Inner squares all the same color gray?

Unit VI: Perception: Perceptual constancy Lightness/Brightness Constancy vs. Color Constancy Lightness/brightness constancy: Level of light changes Image on retina different Colors perceived the same Color constancy: Surroundings change Image on retina the same Color perceived differently

Unit VI: Perception: Perceptual constancy Illusions - Perceptual Constancy & Monocular Cues Constancy: image on retina different brain perceives images as unchanging Most cues: images on retina different brain perceives images as different

Unit VI: Perception: Perceptual interpretation Is our perception learned or are we born with it? Experiments show - both Colin Blakemore Graham Cooper Cambridge - 1970

Unit VI: Perception: Perceptual interpretation Is our perception learned or are we born with it? Kittens – blinders from birth until six months (critical period): Visual cortex didn’t develop Eye works properly – transducts, etc. Visual cortex can’t process

Unit VI: Perception: Perceptual interpretation Is our perception learned or are we born with it? Kittens – blinders from six months until year old: Little effect Period of adaptation; no permanent effect

Unit VI: Perception: Perceptual interpretation Is our perception learned or are we born with it? Kittens – blinders from birth until six months: one eye Little effect Period of adaptation; no permanent effect

Unit VI: Perception: Perceptual interpretation Is our perception learned or are we born with it? Kittens – environment with vertical lines (critical period) Feature detection - horizontal lines don’t develop

Unit VI: Perception: Perceptual interpretation Perceptual adaptation Ability to adapt to changed visual input Example: New glasses Glasses - images upside down Glasses - images left to right Period of adaptation

Unit VI: Perception: Perceptual interpretation Perception and the Human Factor Human factors psychology Help design appliances machines, settings, etc. that fit our natural perceptions Explores how : people and machines interact machines/technology can be adapted to human behaviors “User friendly”

Unit VI: Perception: Perceptual set/mental disposition Mental predisposition to perceive things a certain way Varies, person-to-person Based on several factors

Unit VI: Perception: Perceptual set/mental disposition Do not step on on the grass Perceptual set/mental disposition 1) Schema Assimilation 2) Context 3) Anticipation We see what we expect to see acoindrcg to an Eslnigh usintreviy sdtuy the oerdr of ltteers in a word donset mettar the only tnhig ttahs imtorpnat is that the fsirt and last letetr of every word is in the crrocet potsoiin The rset can be jlembud and one is sltil albe to read the txet wuohtit dilffcutiy

Unit VI: Perception: Perceptual constancy Illusions - Perceptual Constancy & Monocular Cues With many illusions: combination of cues & constancy trick the brain I.e. images on retina is same, but brain perceives them differently because of cues

Unit VI: Perception: Perceptual constancy Illusions - Perceptual Constancy & Monocular Cues Shepard’s table Same images on retina; brain perceives them differently Relative height

Unit VI: Perception: Perceptual constancy Illusions - Perceptual Constancy & Monocular Cues Ponzo Illusion & Shepard’s Monsters Both images same size (same image on our retinas) Linear perspective & relative height: second monster/bar should be further away So should be smaller (relative size) But it’s not, so brain perceives it as larger (size constancy)

Unit VI: Perception: Perceptual constancy Illusions - Perceptual Constancy & Monocular Cues Moon illusion Moon close to horizon appears larger Shrinks as it rises Variant of Ponzo Illusion Relative height + relative size