Perceptual constancies – perception of entire object does not change, even though some of the sensory items have changed Size Constancy Tendency to view an object as constant in size despite changes in the size of the retinal image. Wundt had no way to explain why this happened either, just like the phi phen.
Cognition (mental activity or mental processes) Cognition (Latin: cognoscere, "to know" or "to recognize") refers to the acquisition, storage, transformation, and use of knowledge. Cognition can be natural or artificial, conscious or unconscious. It is a faculty of mental processes such as learning, memory, perception, thinking, problem solving, reasoning, decision making etc.
CharacteristicsThe cognitive processes are active, rather thanpassiveThe cognitive processes are remarkablyefficient and accurateThe cognitive processes Handle positiveinformation better than negative informationThe cognitive processes are interrelated withone another, they do not operate in isolationmany cognitive processes rely on both bottom-up and top-down processing
Sensation and Perception Sensation The processes by which our sense organs receive information from the environment. Transduction The process by which physical energy is converted into sensory neural impulses. Perception The processes by which people select, organize, and interpret sensations.
sensationSensation is defined as:Irreducible elements from which perceptionsare formed as experiences which are simplerand less meaningful than perceptions anduninfluenced by learning and otherpsychological processes such as emotion andmotivation (Hebb, 1972; Scharf, 1975).
Problems of perceptionNo direct physical contact with the visualelements is required to appreciate there nature.How do we form the impressions of thequantitative and qualitative aspects of externalobjects?Does the real physical world actually existindependently of our experience? If so, how wecan come to know its properties and how truthof that knowledge be determined?
Problems…How percepts are constructed from theinteraction of physical energy (light) and theperceiving organism.Proximal and distal stimuli are different butour perceptions are generally accurate orveridical enough to adjust ourselves in theenvironment.Some times percept have propertiesconsiderably different form proximalstimulus.
Components of perceptionDistal stimulusDistal stimulus refers to a physical aspect of theexternal environment, or the physical energywhich comes from the eternal source. Forexample, object in the external environmentsuch as, table, fan etc.Proximal stimulusIt refers to the physical energy coming from theexternal source strikes on the sensory receptors.
Components…Input and outputInput refers to the sensation of stimulus andoutput refers to behavior made in response tothe input.PerceptOut come of perception is known as percept.Recognizing an object as flower would be anexample of percept.
Difference between proximal and distal stimulusMuch of the light coming form distal source isscattered by molecules and lost before it reachesthe receptors of the eye.Resulting proximal image is much smaller,inverted relative to the distal stimulusProximal stimulus is partly under the control ofobserver’s head and eye movements.Information in the form of electromagneticenergy is changed in the neural impulses(transduction).
Defining perceptionAccording to Morgan and King, “perception isthe way the world look (sounds, feels, tastesand smells too)”.According to Zigher (1985), perception refersto the interpretation of sensory information, asa constructive and creative process whichendows sensory experience with meaning.
Defining…Perception is a process by whichindividuals organize and interpret theirsensory impressions in order give meaningto their environment for making betteradjustment with it.Perception is a process by which werecognize and interpret or give meaning toraw material provided by sensory systemwith the help of other psychologicalprocesses such as, learning, memory,emotions and motivation.
Defining… Perception is the process of creating an internal representation of the out side world (internal representation is a joint product of bottom up and top-down processing). Perception is the interpretation of the information provided by sensory system.
Perception is active, selective andrelatively more automatic highermental process through which weexperience or interpret ourimmediate surrounding.
Properties of perceptionPerception is interpretation of physicalenergy or giving meaning to it.In perception, registered stimuli by thesenses are gathered and interpreted with thehelp of previous knowledge.Perception combines aspect of both theoutside world (the stimulus) and innerworld (previous knowledge).
Properties … Perception is relatively more automatic process, required less effort than other cognitive tasks, such as problem solving of decision making. Perception is influenced by other psychological processes such as motivation and emotion. Perception is an active mental process involves both top-down and bottom-up processing.
Concepts in perceptionPhysical- external or internal stimulus suchas wave length, intensity etc.Physiological- stimulation of sensorysystem: neural activity- excitation-inhibition; sensory modality: transductionBehaviorSubjective experience
PerceptionPerceptual OrganizationPerceptual ConstanciesDepth and DimensionPerceptual SetThe World of Illusions
Approaches to perceptionStructuralismWilhelm Wundt and Edward BradfordTitchner (1867-1927)Structuralisms emphasized on the study ofthe structure of perception. Its goal was touncover the simplest, most basic elementsof conscious experience (bottom-upprocessing).
Constructivist ApproachEmphasized on the active nature of perceptual process.Influenced by empiricism.Proposed that the percept is more than the informationcoming form stimulus.Some constructive processes occur within the observer.These are mediating processes between physical worldand its perception.Our perception is a mental construction based on ourcognitive strategies, past experiences, biases,expectations, motives, attention, and other personalcharacteristics
Direct perception approach (James J. Gibson, 1904-1979)Stimulus contains important informationnecessary for perceptionPast experiences are not importantPerception depends on the characteristics ofstimuli (subjective variables are notimportant)It is also known as ecological approachbecause it focuses on the adaptive linkbetween the perceiving organism to itsphysical environment.
Computational Approach (David Marr, 1945-1980)Involves mathematically oriented analysisof certain aspects of visual perceptionderived form computer simulation and AI.Accepts Gibson’s basic idea of directperception but also proposes that perceptionof characteristics such as lines, edges,borders, contours, motion, and otherdiscontinuity.
Beliefs of the information-processing approachInformation is processed in stagesInformation is processed seriallyThe nature of information changes stage tostageInformation processing is affected by severalfactors (noise)It uses both bottom-up and top-down processingIt is a mediating process between input andoutput
Gestalt approach(German: Gestalt - "shape" or "figure")Berlin SchoolKurt Koffka, Max Wertheimer, and WolfgangKöhler (students of Carl Stumpf) are thefounder of this school. The Gestalt or wholeform approach sought to define principles ofperception -- seemingly innate mental lawswhich determined the way in which objectswere perceived.
Gestalt: Basic ideaOperational principle of the brain is holistic,parallel, and analog, with self-organizingtendencies “The whole is greater than the sum of theparts"Opposed to structuralism and WundtGestalt effect refers to the form-formingcapability of our senses particularly visualsense.
Figure and groundProperties of figure groundFigures hold more memorable association thanthe ground.Figures are seen as being in front of the ground.The ground is seen as uniformed material andseems to extend behind the figure.The contour separating the figure from theground appears to belong to the figure.Compared to ground, perception of figure iseffortless
Field forcesCohesive forcesRestraining forces∑ C = ∑ R = no perception (Ganzfeld)∑ C > ∑ R = perception∑ C < ∑ R = unclear or unstable perception
Laws of pragnanzThe fundamental principle of gestaltperception is the law of prägnanz (Germanfor pithiness).The physiological organization will alwaysbe good. Good refers to the simplest andmost stable.We tend to order our experience in amanner that is regular, orderly, symmetric,and simple.
Gestalt laws of perceptual organizationGestalt psychologists modified Law ofprägnanz and given laws whichhypothetically allow us to predict theinterpretation of sensation. These laws arecalled "gestalt laws".
Perceptual Organization Reversible Figures Drawings that one can perceive in different ways by reversing figure and ground.Gestalt Psychology School of thought rooted in the idea that the whole is different from the sum of its parts.
Perceptual OrganizationGestalt Laws of GroupingProximity Seeing 3 pair of lines in ASimilarity Seeing columns of orange and red dots in BContinuity Seeing lines that connect 1 to 2 and 3 to 4 in CClosure Seeing a horse in D
Gestalt Perceptual Psychology Laws of Perceptual Organization Law of Similarity
Gestalt Perceptual Psychology Laws of Perceptual Organization Law of Proximity (nearness)
General Perceptual Psychology Principles of Perceptual Organization The principle of common region
General Perceptual Psychology Principles of Perceptual Organization The principle of common region
General Perceptual Psychology Principles of Perceptual Organization The principle of connectedness
General Perceptual Psychology Principles of Perceptual Organization The principle of synchrony (objects that change together are grouped together)
General Perceptual Psychology Principles of Perceptual Organization Repetition Discrimination Task - groupings influence perception and speed of search:
Perceptual Segregation Figure-ground segregation-We are primed to see a figure in front of a background Symmetry and perception of figure and ground
Perceptual Segregation Figure-ground segregation-We are primed to see a figure in front of a background Area size and perception of figure and ground
Perceptual Segregation Figure-ground segregation-We are primed to see a figure in front of a background Orientation and perception of figure and ground
Perceptual Segregation Figure-ground segregation-We are primed to see a figure in front of a background Meaningfulness and perception of figure and ground
Pattern recognitionPattern recognition and attention preparethe raw sensory information for morecomplex mental process.Pattern recognition allows us to perceive aform in a stimulus and attention isresponsible for our more extensiveprocessing of some information.Pattern recognition is the identification ofcomplex arrangement of sensory stimuli.
In pattern recognition raw information isorganized and transformed by sensoryprocess and compared with information inother memory storage.Thus, pattern recognition involves realizingthat a particular pattern is seen before.
Bottom up processing (Data driven)• emphasizes importance of stimulus in PR.• Information coming from the stimulus is enough to recognize the pattern.• Recognition process in initiated by the parts of the pattern which serves as the basis for the recognition of whole.
Top down processing (conceptually driven) Emphasizes that concept and high level of processing influence PR. Our knowledge about the world help us identifying patterns. The process of PR is initiated by a hypothesis about the whole leading to the identification of whole and the subsequent recognition of components.
How do we recognize patterns?Do we identify an object because we havefirst recognize it’s components or do werecognize these part because we have firstidentified the object?The problem that, whether the recognitionprocess is initiated by the parts of the patternor whether it is initiated by a hypothesisabout the whole (hypothesis testing) iscalled prasing paradox.
A: Template Matching Theory Templates are specific patterns that are stored in memory. Stimulus is compared with a set of templates. We recognize the stimulus as the template that matches most closely. Stimulus must fit the template precisely.
Problems of TMTIf a number of templates match or come close (not one)- We need further processing to sort out which template is most appropriate which will take much time than it actually takes. It does not explain how perception works. with the development of technology our experiences change thus, how and when templates are created?
How different patterns are recognized assame despite the wide variation in the size,shape, orientation etc. (e.g. recognizinghand writing of different people).It works for simple latter and simple objects.
B: Feature Analysis Feature analysis model assumes that instead of processing stimuli as whole units, we break them down into their components. We recognized those parts to infer what the whole represents. There is physiological mechanism in retina and in the cortex. These are called feature detectors. Some cells respond to boarders between light and dark called edge detectors. Movement detectors are called bug detectors. Horizontal and vertical line detectors are also found in the cortex.
1: Distinctive feature approach Discrimination among letters is made on the basis of small no of characteristics called distinctive features. We store a list of feature components for each letter. E.g. Q has a round closed shape and a diagonal line. Gibson (1969) demonstrated that people require long time to decide whether some letters are different from one another when the letter share large number of critical features.
For example, P and R are similar on a largenumber of critical features; and G and M aredifferent from each other on a large number ofcritical features.Differentiation between G and M takes less time ascompared to differentiation between P and R.In distinctive feature approach pattern recognitioninvolves detecting specific important parts while inTMT emphasizes prototype and entire recognitionof entire shape.
Problems of distinctive feature approach Explain simple shape or features recognition such as letter recognition. It does not explain physical relationships. For example, T and L are similar but they are recognize distinctly on the basis of relationship. For example, T has a vertical line supports a horizontal line in the middle. Where L has the vertical line rests at the side of the horizontal line. It explains simple letter recognition but natural features, shapes are more complex. How can we recognize a horse?
2: The Computational Approach (David Marr (1982)Images- Identification of object’s edges bycombining intensity of the imagePrimal sketch- edges are organized intoabstract representation2 ½ D sketch- primal sketch is convertedinto 2 ½ D sketch (contours, shade, roughdepth)3 D image- Describes shapes and their spatialorganization of the object.
Perceptual OrganizationIdentifying Objects Geons (geometric icons) are simple 3D component shapes. A limited number are stored in memory. Geons are combined to identify essential contours of objects.
Perceptual Constancies Size Constancy The tendency to view an object as constant in size despite changes in the size of the retinal image. Shape Constancy The tendency to see an object as keeping its form despite changes in orientation.
Perceptual Constancies The Ames RoomA specially-built room thatmakes people seem tochange size as they movearound in itThe room is not arectangle, as viewersassume it is.A single peephole preventsusing binocular depth cues.
Perceptual Constancies Shape Constancy Even though these images cast shadows of different shapes, they still are seen as round.
Perceptual ConstanciesSize Constancy Tendency to view an object as constant in size despite changes in the size of the retinal image. http://www.psychologie.tu-dresden.de/i1/kaw/diverses%20Material/www.illusionworks.com/assets/images/constancy.jpg
Binocular CuesDepth cues thatrequire the use ofboth eyesEnables people to seein three dimensions.
Retinal DisparityA binocular depth cue resulting fromslightly different images produced bythe separation of the retinas in the leftand right eyeIs most effective when the item is quiteclose to the person
Retinal Disparity Demo1. Roll a piece of scrap paper into a tube shape.2. Hold it to your right eye as if it were a telescope3. Look through the tube focusing on an object on a blank wall in front of you.4. Keeping both eyes open, hold your open left hand beside the tube…continue to focus on the object on the wall.5. The images should fuse and ….
ConvergenceA binocular depth cue related to thetension in the eye muscles when theeyes track inward to focus on objectsclose to the viewerThe more tension in the eye muscle, thecloser the object isWorks best at close distances
Monocular CuesDepth cues that require the use of onlyone eye
Monocular Depth Cues 1. Relative SizeUsing the perceivedsize of a familiarobject to determinedepthThe larger theobject appears, thecloser the object isto the viewer
Monocular Depth Cues 2. Relative MotionA person who is moving can determinedepth by focusing on a distant object.Objects further away than the object offocus will appear to move in the samedirection as the subject is moving.Objects closer than the object of focuswill appear to move in the oppositedirection.
Monocular Depth Cues 4. Relative HeightMethod ofdetermining depthby noting thatdistant objectsappear higher inyour field ofvision than docloser objects
Monocular Depth Cues 5. Texture GradientMethod of determining depth by noting that distant objects have a smoother texture than nearby objects Can see individual blades of hay, but in the Distance, the hay seems to have a smoother Texture.
Monocular Depth Cues 6. Relative ClarityMethod ofdeterminingdepth by notingthat distantobjects are lessclear thannearby objectsTends to work Paris Street: A Rainy Day by Gustaveoutdoors Caillebotte
Monocular Depth Cues 7. Linear PerspectiveMethod ofdetermining depthby noting thatparallel lines appearto converge in thedistance As parallel lines become moreThe lines appears to distant from us, they appear to get closer together - like the sides ofeventually merge on the gray bit at left. Theirthe horizon. apparent closeness is therefore a cue to their relative distance from us.
Depth and Dimension 8.The Visual CliffDevised by EleanorGibson and Richard Walkto test depth perception ininfants and animals.Provides visual illusion ofa cliff.Caregiver stands acrossthe gap.Babies are not afraid untilabout the age they cancrawl.
Perceptual Set What is seen in the center figures depends on the order in which one looks at the figures: If scanned from the left, a man’s face is seen. If scanned from the right, a woman’s figure is seen.
Perceptual Set Context Effects The same physical stimulus can be interpreted differently depending on perceptual set, e.g., context effects. When is the middle character the letter B and when is it the number 13?
The World of Illusions The Müller-Lyer IllusionIllusion in whichthe perceivedlength of a line isaltered by theposition of otherlines that enclose it
The World of IllusionsThe Ponzo Illusion Illusion in which the perceived line length is affected by linear perspective cues. Side lines seem to converge Top line seems farther away But the retinal images of the red lines are equal.
The Continuing ControversyThe ganzfield procedureResearchers disagree about the reliability ofstudies done to replicate the ganzfield test.Visit www.randi.org/ for information aboutthe James Randi Educational Foundation’smillion-dollar paranormal challenge.