Sensation and Perception Sensation and Perception True or False??? True or False??? 1. 1. On a clear, dark night most of us can On a clear, dark night most of us can see a candle flame 30 miles away. see a candle flame 30 miles away. 2. 2. Advertisers are able to shape our Advertisers are able to shape our buying habits through subliminal buying habits through subliminal messages. messages. 3. 3. Constant eye movements prevent our Constant eye movements prevent our vision from being seriously vision from being seriously disrupted. disrupted.
Transcript
Sensation and PerceptionSensation and Perception
True or False???True or False???
1.1. On a clear, dark night most of us can On a clear, dark night most of us can see a candle flame 30 miles away.see a candle flame 30 miles away.
2.2. Advertisers are able to shape our Advertisers are able to shape our buying habits through subliminal buying habits through subliminal messages.messages.
3.3. Constant eye movements prevent our Constant eye movements prevent our vision from being seriously disrupted.vision from being seriously disrupted.
Introducing,Introducing,….Sensation!….Sensation!
““Seeing is believingSeeing is believing.”.”
For each of the following For each of the following visuals, simply write down visuals, simply write down what you see. (Do not share what you see. (Do not share with your neighbor.)with your neighbor.)
Analyzing what we see….Analyzing what we see….
Each visual provides sensory Each visual provides sensory information that gives rise to two information that gives rise to two totally different perceptual totally different perceptual interpretations.interpretations.
Now, lets try it again…Now, lets try it again… Write down what you see Write down what you see firstfirst in the in the
next visual image.next visual image.
Sensation and visual imagesSensation and visual images
Why is it that no matter how many Why is it that no matter how many times we look at the image, we tend times we look at the image, we tend to see the image we saw the first to see the image we saw the first time we observed it?time we observed it?First impression = schemaFirst impression = schemaHave to consciously seek the other Have to consciously seek the other
figurefigureAfter practice, we can see both images, After practice, we can see both images,
but not simultaneouslybut not simultaneously
So, what isSo, what is Sensation & Sensation & Perception?Perception?
SensationSensation How we detect physical energy How we detect physical energy
from the environment and encode from the environment and encode it as neural signals (what we it as neural signals (what we sense and send to the brain)sense and send to the brain)
PerceptionPerception How we select, interpret and How we select, interpret and
organize this information (what the organize this information (what the brain does with it)brain does with it)
In other words…In other words…
Sensation provides the raw Sensation provides the raw information that perception information that perception constructs into our experiencesconstructs into our experiences
SensationSensation : :
The Forest Has EyesThe Forest Has Eyes
sensation sensation and and perceptioperception work n work together together to sort to sort out out complex complex processesprocesses
SensationSensation
Bottom-Up ProcessingBottom-Up Processing Sensory analysis that begins with the Sensory analysis that begins with the
sense receptors and works up to the sense receptors and works up to the brain’s integration of sensory brain’s integration of sensory informationinformation
Top-Down ProcessingTop-Down Processing information processing guided by information processing guided by
higher-level mental processeshigher-level mental processes we construct perceptions drawing on we construct perceptions drawing on
our experience and expectationsour experience and expectations
Top Down ProcessingTop Down Processing
Aoccdrnig to rscheearch at Cmabridge Aoccdrnig to rscheearch at Cmabridge Uinervtisy, it deosn’t mttaer in what Uinervtisy, it deosn’t mttaer in what oredr the ltteers in a word are, the oredr the ltteers in a word are, the olny iprmoetnt tihng is that the frist olny iprmoetnt tihng is that the frist and lsat ltteer be at the rghit pclae. and lsat ltteer be at the rghit pclae. The rset can be a total mses and you The rset can be a total mses and you can still raed it wouthit a porbelm. can still raed it wouthit a porbelm. This is bcuseae the huamn mnid This is bcuseae the huamn mnid deos not raed ervey lteter by istlef, deos not raed ervey lteter by istlef, but the word as a wlohe.but the word as a wlohe.
Top Down ProcessingTop Down Processing
How were you able to immediately How were you able to immediately make sense of these scrambled make sense of these scrambled words?words?
Our Our experienceexperience and and expectationsexpectations enable us to immediately perceive the enable us to immediately perceive the scrambled letters as meaningful words scrambled letters as meaningful words and sentences.and sentences.
a.a. Place one finger on any line composing Place one finger on any line composing the spiral. the spiral.
b.b. Place a finger from your other hand Place a finger from your other hand beside it and begin tracing the circle beside it and begin tracing the circle while holding your first finger in place. while holding your first finger in place.
c.c. What happens?What happens?
Failures of PerceptionFailures of Perception Prosopagnosia: complete sensation Prosopagnosia: complete sensation
but incomplete perception (“face but incomplete perception (“face blindness”)blindness”)– Can sense visual information, but can’t Can sense visual information, but can’t
recognize it (can’t relate stored recognize it (can’t relate stored knowledge to sensory input)knowledge to sensory input)
– Damage to temporal lobe area Damage to temporal lobe area (recognition)(recognition)
Gustav FechnerGustav FechnerPioneer in PsychophysicsPioneer in Psychophysics
1801-1887 (U. of Leipzig)1801-1887 (U. of Leipzig) Theory: consciousness Theory: consciousness
and matter coexistand matter coexist Mind / body: two aspects Mind / body: two aspects
of fundamental unityof fundamental unity Stared at sun! Afterimage Stared at sun! Afterimage
of blue and yellowof blue and yellow Mathematical relationship Mathematical relationship
b/n force of stimuli and b/n force of stimuli and intensity of sensationintensity of sensation
Sensation- ThresholdsSensation- Thresholds
Absolute ThresholdAbsolute Threshold minimum stimulation needed to detect minimum stimulation needed to detect
a particular stimulus 50% of the timea particular stimulus 50% of the time Difference ThresholdDifference Threshold
minimum difference between two minimum difference between two stimuli required for detection 50% of the stimuli required for detection 50% of the timetime
just noticeable difference (JND)just noticeable difference (JND)
Absolute thresholdAbsolute threshold
““An absolute threshold is anything An absolute threshold is anything but absolute…”but absolute…”
– Why is this? What factors typically Why is this? What factors typically affect the absolute threshold?affect the absolute threshold? RepetitionRepetition FatigueFatigue Competing stimuliCompeting stimuli ExpectationExpectation
Sensation- ThresholdsSensation- Thresholds Signal Detection TheorySignal Detection Theory
predicts how and when we detect the predicts how and when we detect the presence of a faint stimulus (signal) amid presence of a faint stimulus (signal) amid background stimulation (noise)background stimulation (noise)
assumes that there is no single absolute assumes that there is no single absolute thresholdthreshold
detection depends partly on person’sdetection depends partly on person’s experienceexperience expectationsexpectations motivationmotivation level of fatiguelevel of fatigue
Sensation- ThresholdsSensation- Thresholds
SubliminalSubliminal When stimuli When stimuli
are below are below one’s absolute one’s absolute threshold for threshold for conscious conscious awarenessawareness
0
25
50
75
100
Low Absolutethreshold
Medium
Intensity of stimulus
Percentageof correctdetections
Subliminal stimuli
19571957
James VicaryJames Vicary 1/3000 second1/3000 second RepetitionRepetition Sales increaseSales increase
The average The average American will see American will see over 6 million ads over 6 million ads in a lifetime…in a lifetime…
Appeal to the Appeal to the subconscious will subconscious will make consumer make consumer feel more feel more positively about a positively about a productproduct
Sensation- ThresholdsSensation- Thresholds
Weber’s Law-Weber’s Law- to perceive as to perceive as different, two stimuli must differ different, two stimuli must differ by a constant minimum percentage by a constant minimum percentage (Difference thresholds grow with (Difference thresholds grow with magnitude of stimulus)magnitude of stimulus) light intensity- 8%light intensity- 8% weight- 2%weight- 2% tone frequency- 0.3%tone frequency- 0.3%
Weber’s LawWeber’s Law
As a salesman, how might one use As a salesman, how might one use Weber’s law to increase chances of Weber’s law to increase chances of selling the following to one selling the following to one customer?customer?
A.A. Built in ipod accessory: $100Built in ipod accessory: $100
Sensory adaptation-Sensory adaptation- diminished diminished sensitivity as a consequence of sensitivity as a consequence of constant stimulationconstant stimulation
Eyes: constant quiver to ensure Eyes: constant quiver to ensure enough continual stimulation to eye’s enough continual stimulation to eye’s receptorsreceptors
Otherwise full visual image is lostOtherwise full visual image is lost
Vision- Stabilized Vision- Stabilized Images on the RetinaImages on the Retina
VisionVision How do we transform particles of How do we transform particles of
light into meaningful images?light into meaningful images?
TransductionTransduction conversion of one form of energy to conversion of one form of energy to
anotheranother in sensation, how our sensory in sensation, how our sensory
systems transform stimulus energies systems transform stimulus energies into neural impulsesinto neural impulses
VisionVision TwoTwo physical characteristics of light help physical characteristics of light help
determine how we visually sense them…determine how we visually sense them…
1. Wavelength1. Wavelength the distance from the peak of one wave to the the distance from the peak of one wave to the
peak of the next (determines peak of the next (determines huehue)) Hue:Hue: color we see determined by wavelength of color we see determined by wavelength of
lightlight
2. Intensity2. Intensity amount of energy in a light wave determined by amount of energy in a light wave determined by
Vision- Physical Properties of Vision- Physical Properties of Waves (from an atom to a Waves (from an atom to a
mile…)mile…)Short wavelength=high frequency
(bluish colors, high-pitched sounds)
Long wavelength=low frequency(reddish colors, low-pitched sounds)
Great amplitude(bright colors, loud sounds)
Small amplitude(dull colors, soft sounds)
The spectrum of electromagnetic energy: (light that we transduce into color)
VisionVision
Match the followingMatch the following
1.1. CorneaCorneaDD
2.2. Pupil Pupil AA
3.3. Iris Iris BB
4.4. LensLensCC
5.5. RetinaRetinaEE
a.a. Adjustable opening in Adjustable opening in the center of the eyethe center of the eye
b.b. Ring of muscle, color Ring of muscle, color portion of the eye portion of the eye around pupil- controls around pupil- controls size of pupil openingsize of pupil opening
c.c. Transparent- behind Transparent- behind pupil, changes shape pupil, changes shape to focus images on to focus images on retinaretina
d.d. Protects eye, bends Protects eye, bends light to provide light to provide focusfocus
e.e. Eyes light sensitive Eyes light sensitive inner surface- rods, inner surface- rods, cones, neurons that cones, neurons that process visual info.process visual info.
VisionVision
AccommodationAccommodation- the eye’s lens - the eye’s lens changes shape to help focus near or changes shape to help focus near or far objects on the retinafar objects on the retina
Retina-Retina- the light-sensitive inner the light-sensitive inner surface of the eye, containing surface of the eye, containing receptor rods, cones and layers of receptor rods, cones and layers of neurons that begin the processing of neurons that begin the processing of visual information visual information
Retina’s Reaction to Retina’s Reaction to Light- ReceptorsLight- Receptors
RodsRods peripheral retina peripheral retina detect black, white and graydetect black, white and gray twilight or low lighttwilight or low light
ConesCones near center of retina near center of retina fine detail and color visionfine detail and color vision daylight or well-lit conditions daylight or well-lit conditions
Rods and ConesRods and Cones
Making sense of our vision…Making sense of our vision…
So why is our peripheral vision more So why is our peripheral vision more blurred than our focused vision? (in blurred than our focused vision? (in front of us)front of us)Cones = center of retinaCones = center of retinaRods = periphery of retinaRods = periphery of retina
How do you walk effectively on a trail How do you walk effectively on a trail on a very dark night? Why?on a very dark night? Why?
Why can a cat see better than us at Why can a cat see better than us at night?night?
Vision- ReceptorsVision- Receptors
Receptors in the Human Eye
Cones Rods
Number
Location in retina
Sensitivity in dim light
Color sensitive? Yes
Low
Center
6 million
No
High
Periphery
120 million
From the eye to the brainFrom the eye to the brain……
Optic NerveOptic Nerve Rope-like Rope-like
axons from axons from ganglion cells- ganglion cells- carries carries information information from the eye to from the eye to the brain the brain (1,000,000 (1,000,000 messages at messages at once!)once!)
Close your left eye- move forward Close your left eye- move forward to a spot in which the car to a spot in which the car disappears. What is this called? disappears. What is this called? How do we explain it?How do we explain it?
Retina’s Reaction to Retina’s Reaction to LightLight
Blind Spot-Blind Spot- point at which the optic nerve point at which the optic nerve leaves the eye- creates “blind spot” leaves the eye- creates “blind spot” because no receptor cells located therebecause no receptor cells located there
FoveaFovea- central point in the retina, around - central point in the retina, around which the eye’s cones cluster which the eye’s cones cluster (contains (contains only cones- direct connection to visual only cones- direct connection to visual cortex through bipolar cells = fine detail)cortex through bipolar cells = fine detail)
VisionVision AcuityAcuity- the sharpness of vision- the sharpness of vision NearsightednessNearsightedness- nearby objects are - nearby objects are
seen more clearly than distant seen more clearly than distant objects because distant objects objects because distant objects in in frontfront of retina of retina
Farsightedness-Farsightedness- faraway objects are faraway objects are seen more clearly than near objects seen more clearly than near objects because the image of near objects is because the image of near objects is focused focused behindbehind retina retina
Pathways from the Eyes Pathways from the Eyes to the Visual Cortexto the Visual Cortex
Visual Information Visual Information ProcessingProcessing
Retina: Brain tissue Retina: Brain tissue / analyzes, encodes / analyzes, encodes info & routes to info & routes to ThalamusThalamus
Process becomes Process becomes more complex as more complex as continuescontinues
Visual Information Visual Information ProcessingProcessing
Feature DetectorsFeature Detectors(Hubel and Wiesel, 1979)(Hubel and Wiesel, 1979)
nerve cells in the nerve cells in the visual cortex that visual cortex that respond to respond to specific features specific features (send to specific (send to specific parts of cortex)parts of cortex) shapeshape angleangle movementmovement
Stimulus
Cell’s responses
How does this explain How does this explain Prosopagnosia?Prosopagnosia?
The Key to PerceptionThe Key to Perception Perception = combining sensory Perception = combining sensory
input with assumptions, expectationsinput with assumptions, expectations
How the Brain PerceivesHow the Brain PerceivesStare at the Necker Cube. What Stare at the Necker Cube. What
happens?happens?
How can we explain our How can we explain our changing perception of the changing perception of the
Necker Cube?Necker Cube?
Same image continues to meet your Same image continues to meet your retina, your brain constructs varying retina, your brain constructs varying perceptions every couple of seconds.perceptions every couple of seconds.
Illusory ContoursIllusory ContoursStare at the center of the Stare at the center of the
imageimage
Parallel ProcessingParallel Processing simultaneous processing of several simultaneous processing of several
aspects of visual stimulus (color, aspects of visual stimulus (color, depth, movement, form- different parts depth, movement, form- different parts of cortex integrate all info at once to of cortex integrate all info at once to form perception)form perception)
Parallel ProcessingParallel Processing
Facial recognition = 30% of cortexFacial recognition = 30% of cortex Neural networks: synchronized Neural networks: synchronized
integrationintegration– ¼ of second- neurons, parts of brain ¼ of second- neurons, parts of brain
collaborate at once(40 impulses per collaborate at once(40 impulses per
““Light rays are not colored. Light rays are not colored. Color, like all aspects of vision, Color, like all aspects of vision, resides not in the object but in resides not in the object but in the theater of our brains.”the theater of our brains.”
Isaac Newton, 1704Isaac Newton, 1704
Visual Information Visual Information ProcessingProcessing
Trichromatic (three color) TheoryTrichromatic (three color) Theory Young and HelmholtzYoung and Helmholtz three different retinal color receptorsthree different retinal color receptors
redred greengreen BlueBlue
Combination of these cones = other colorsCombination of these cones = other colors
Color-Deficient VisionColor-Deficient Vision
MonochromatMonochromaticic
DichromaticDichromatic
DichromaticDichromatic
Visual Information ProcessingVisual Information Processing
Opponent-Process Theory-Opponent-Process Theory- opposing retinal opposing retinal processes enable color vision (in retina& processes enable color vision (in retina& thalamus, some neurons turned on/off by thalamus, some neurons turned on/off by certain colors)certain colors)
““ON”ON” “OFF”“OFF”
redred greengreen
greengreen redred
blueblue yellowyellow
yellowyellow blueblue
black black whitewhite
white white blackblack
Visual Information Visual Information ProcessingProcessing
Color ConstancyColor Constancy Perceiving familiar objects as Perceiving familiar objects as
having consistent color, even if having consistent color, even if changing illumination alters the changing illumination alters the wavelengths reflected by the wavelengths reflected by the object (perception of color comes object (perception of color comes from object and those things from object and those things around it)around it)
