2Some Questions of Interest How can we perceive an object like a chair as having a stable form, given that the image of the chair on our retina changes as we look at it from different directions?
3Some Questions of Interest What are two fundamental approaches to explaining perception?What happens when people with normal visual sensations cannot perceive visual stimuli?
4Perception Is…The process of recognizing, organizing, and interpreting informationHow do you recognize these items?
5Basic Concepts Distal object Informational medium Proximal stimulation Grandma’s faceInformational mediumReflected light from Grandma’s faceProximal stimulationPhoton absorption in the rod and cone cells of the retinaPerceptual object
6Perceptual Basics Sensory adaptation Our senses respond to change Occurs when sensory receptors change their sensitivity to the stimulusConstant stimulation leads to lower sensitivityOur senses respond to changeGanzfeld effect
7Perceptual Illusions Sometimes we cannot perceive what does exist Sometimes we perceive things that do not existINSERT FIG 3.3 & FIG 3.4
8Perceptual Illusions Sometimes we perceive what cannot be there INSERT FIG 3.5
9Perceptual Illusions Some other illusions to explore:
10Our Visual SystemLight travels through the eye and focuses on the retinaElectromagnetic light energy is converted into neural electrochemical impulsesINSERT FIG 3.7
11Our Visual System Three main layers of neural tissue in retina Ganglion cellsAmacrine cells, horizontal cells, bipolar cellsPhotoreceptorsRods and conesINSERT FIG 3.8
12Visual Pathways in the Brain What/where hypothesisOne path for identifyingTemporal lobe lesions in monkeysCan indicate where but not whatAnother for spatially locatingParietal lobe lesions in monkeysCan indicate what but not where
13Visual Pathways: Alternative What/how hypothesisWhere something is located in spaceHow do we reach for it?
14Theories of Perception Bottom-up theoriesParts are identified, put together, and then recognition occursTop-down theoriesPeople actively construct perceptions using information based on expectations
15Bottom-Up Processing Theories Bottom-Up Processing TheoriesDirect perceptionTemplate theoriesFeature-matching theoriesRecognition-by-components theory
16Gibson’s Theory of Direct Perception The information in our sensory receptors is all we need to perceive anythingDo not need the aid of complex thought processes to explain perception
17Gibson’s Theory of Direct Perception Use texture gradients as cues for depth and distanceAllows us to perceive directly the relative proximity or distance of objectsINSERT FIG 3.10
18Gibson’s Theory of Direct Perception Mirror neurons start firing ms after a visual stimulusINSERT VIDEO #18, Mirror Neurons
19Template Theories Basics of template theories Template TheoriesBasics of template theoriesMultiple templates are held in memoryTo recognize the incoming stimuli, you compare to templates in memory until a match is foundOne click to view the words “See Stimuli” and then the demonstration will illustrate the template theory. All images obtained from Microsoft clips.Search memory for a matchSee stimuli
20Template Theories Weakness of theory Problem of imperfect matches Template TheoriesWeakness of theoryProblem of imperfect matchesCannot account for the flexibility of pattern recognition systemOne click to view the words “See Stimuli”, then the demonstration of the weakness of the theory will occur. All images taken from Microsoft clips.If these clips are being removed, then you can INSERT FIG 3.11 insteadSearch for match in memorySee stimuliNo perfect match in memory
21Feature-Matching Theories Feature-Matching TheoriesRecognize objects on the basis of a small number of characteristics (features)Detect specific elements and assemble them into more complex formsBrain cells that respond to specific features such as lines and angles are referred to as “feature detectors”
22Pandemonium Model Four kinds of demons Image demons Feature demons Cognitive demonsDecision demonsINSERT FIG 3.12
23Navon (1977) Participants asked what they saw on the Global levelLocal levelGlobal precedence effect found when letters were closer together.INSERT FIG 3.13 & FIG 3.14Results depended on whether letters are more widely spacedParticipants were faster at identifying local features of the letters
24Physiological Evidence for Features Physiological Evidence for FeaturesHubel & Wiesel (1979)Simple cells detect bars or edges of particular orientation in particular locationComplex cells detect bars or edges of particular orientation, exact location abstractedHypercomplex cells detect particular colors (simple and complex cells), bars, or edges of particular length or moving in a particular directionINSERT FIG 3.15
25Recognition-by-Components (RBC) Theory Recognition-by-Components (RBC) TheoryBiederman (1987)Describes how 3D images are identifiedBreaks objects down into geonsObjects are identified by geons, relationship between themINSERT FIG 3.16
26Evidence for Geons Biederman & Cooper (1991) Evidence for GeonsBiederman & Cooper (1991)Used visual priming to demonstrate the existence of geons in a picture naming taskSubjects were shown a series of fragmented pictures and were asked to identify the objectsBUT there are neurons sensitive to viewpoint-invariant propertiesBiederman, I., & Cooper, E. E. (1991). Priming contour-deleted images: Evidence for intermediate representations in visual object recognition. Cognitive Psychology, 23,
27Top-Down Processing (Constructive Approach) Top-Down Processing (Constructive Approach)Perception is not automatic from raw stimuliProcessing is needed to build perceptionTop-down processing occurs quickly and involves making inferences, guessing from experience, and basing one perception on another
28Evidence for Top-Down Processing Evidence for Top-Down ProcessingContext effectsINSERT FIG 3.9
29Configural-Superiority Effect Objects presented in context are easier to recognize than objects presented aloneTask: Spot the different stimuli, press buttonINSERT FIG 3.17
30Configural-Superiority Effect TargetCompositePomerantz (1981)Measure reaction time Target alone = 1884 Composite = 749 Target spotted faster in a context!
31Which Approach Is Right? Top-down or bottom-upPerhaps a bit of both
32Object Perception Viewer-centered representation Object is stored in the perspective seenStore multiple views of object as seen under various conditionsViewpoint dependent processObject-centered representationObject is stored in a way that best represents the objectViewpoint invariant processRealism Link: Why is this important?Understanding how information is coded in our minds helps us to better understand how to create computers that can also perceive objects or to enhance our own recognition abilities.
33Object Perception Evidence supports both How to reconcile? Maybe both contribute to object recognitionTwo ends of a continuum that contribute to object recognitionBurgund & Tarr researched this issue
34Landmark-Centered Orientation Information is coded by its relation to a well-known or prominent itemConsider your college campusWhat is a prominent item you use to orient yourself on campus?
35Gestalt’s View of Perception Basic tenet“The whole is more than a sum of its parts”Law of PrägnanzIndividuals organize their experience in as simple, concise, symmetrical, and complete manner as possible
36Gestalt’s Principles of Visual Perception INSERT FIG 3.18
37Gestalt’s Principles of Visual Perception Figure-groundOrganize perceptions by distinguishing between a figure and a backgroundProximityElements tend to be grouped together according to their nearnessSimilarityItems similar in some respect tend to be grouped togetherINSERT FIG 3.19
38Gestalt’s Principles of Visual Perception BContinuityBased on smooth continuity, which is preferred to abrupt changes of directionClosureItems are grouped together if they tend to complete a figureSymmetryPrefer to perceive objects as mirror imagesADCCheck out Kanizsa’s figure at It appears as if a white square were in front of four black circles, representing both closure and symmetry.
39Pattern Recognition Systems Feature analysis systemRecognize parts of objectsAssemble parts into wholesConfigurational systemRecognize larger configurations
40Evidence for Separate Systems Tanaka & Farah (1993)Participants studiedFaces and namesPictures of homes and home owner’s namesAt test, given only a piece of face (e.g., nose), whole face, whole home, or a piece of the home (e.g., window)Asked to recall names
41Tanaka & Farah (1993) Results People have more difficulty recognizing parts of faces than parts of housesINSERT FIG 3.21
42Fusiform Gyrus in Temporal Lobe Implicated in pattern recognitionStudies illustrate it is active in facial recognitionHowever, also active if high expertise in any item (birds, cars) recognitionExpert individuation hypothesis
43Evidence for Separate Systems ProsopagnosiaInability to recognize faces after brain damageAbility to recognize objects is intactAssociative agnosiaDifficulty with recognizing objectsCan recognize faces
44Perceptual ConstancyObject remains the same even though our sensation of the object changesSize constancy vs. shape constancyINSERT FIG 3.23 & FIG 3.24
45Depth PerceptionThe ability to see the world in three dimensions and detect distanceVision only has a two-dimensional viewWe must interpret the information given to perceive depthWe take flat images and create a three-dimensional viewOptical illusions demonstrate that this interpretation does not always have to be correct
46Monocular Depth Cues Texture gradients Relative size Interposition Grain of itemRelative sizeBigger is closerInterpositionCloser are in front of other objectsTeaching Tip: Use a photograph to illustrate cues these cues. Microsoft clips is a good starting point.
47Monocular Depth Cues Linear perspective Aerial perspective Parallel lines converge in distanceAerial perspectiveImages seem blurry farther awayMotion parallaxObjects get smaller at decreasing speed in distanceTeaching Tip: Use a photograph to illustrate cues these cues. Microsoft clips is a good starting point.
48Binocular Depth Cues Binocular convergence Binocular disparity Eyes turn inward as object moves toward you; brain uses this information to judge distanceBinocular disparityEach eye views a slightly different angle of an object; brain uses this to create a 3D image
49Agnosias, Ataxias, & Cognition Demonstrate the modularity of cognitionHelp us to understand what brain locations are associated with different types of higher-level processingProvide us with a model of how normal processing must work
50Deficits in Perception Disruption of the “what” pathwayAgnosiaInability to recognize and identify objects or people, despite having knowledge of the characteristics of the objects or peopleShows the specialization of our perceptual systems
51Deficits in Perception Disruption of the “what” pathwaySimultagnosicNormal visual fields, yet act blindPerceives only one stimulus at a time—single word or object
52Deficits in Perception Disruption of the “what” pathwayProsopagnosiaInability to recognize faces, including one's ownCannot recognize person from faceKnows a face is a face Can recognize individuals from voiceCan recognize objectsCan discriminate whether two faces are same or different
53Deficits in Perception Disruption of the “how” pathwayOptic ataxiaCannot use vision to guide movementUnable to reach for items