KMF1023 Chapter 3 Perception Part 1 PDF 2017

Unit 3 Part 1 Visual Perception KMF 1023 COGNITIVE PSYCHOLOGY FSKPM Universiti Malaysia Sarawak 1 2 3 4  In this topic, we will learn about: Perception – How does the process of perception take place? – Two important processes: botto...

Unit 3 Part 1 Visual Perception KMF 1023 COGNITIVE PSYCHOLOGY FSKPM Universiti Malaysia Sarawak 1 2 3 4  In this topic, we will learn about: Perception – How does the process of perception take place? – Two important processes: bottom-up vs top-down process Bottom-up processing: – How do we analyse objects into features in the early process of perception? FIT Theory vs RBC Theory Top-down Processing: – How are elements of a scene organised into objects? Gestalt Approach Evidence that perception is an intelligent activity – Some behavioral and physiological evidence 5  How does Perception take place? Why is something easy like looking at a scene becomes complicated when we look at the mechanisms involve? How does our brain store information about our perception of the world? 6  How does Perception take place? Two important basic processes in perception – Bottom-up processing – Top-down processing 7  How does Perception take place? Bottom up processing – Data based processing – Processing based on data received from stimulus (eg. light) – No incoming data, no perception 8  How does Perception take place? Top-down processing – Knowledge-based processing – Processing that is based on knowledge – Knowledge of a context can influence one’s perception 9  The case of Misperception Light from the streetlight is reflected from the sign into Roger’s eye, which creates a pattern representing the street sign on Roger’s retina. 10  The case of Misperception (Interpretation) (Transduction & Transformation) The pattern on the retina is transformed into electrical signals, which are transmitted to the brain and processed. 11  Data + Knowledge = Perception Roger’s perception of the sign is created by the processing of the incoming data provided by the pattern of light entering his eye (bottom-up processing) plus the influence of existing knowledge and expectations (top-down processing). 12  Demonstration of bottom-up and top-down processing The rat-man demonstration Divide class into 2 groups – One group to see stimulus A, another group sees stimulus B – Both groups are then shown Picture A 13 Demonstration of bottom-up and top-down processing Stimulus A 14 Demonstration of bottom-up and top-down processing What do you see in this picture ? 15 Demonstration of bottom-up and top-down processing Stimulus B 16 Demonstration of bottom-up and top-down processing What do you see in this picture ? Why do the two different groups give different answers? 17  Demonstration of bottom-up and top-down processing Stimulus A – data – starting point for bottom up processing When you look at the picture after you have looked at Stimulus A, an expectation is created – This expectation = knowledge = top-down processing – Top-down processing influences your perception of Picture A – “We see only what we know” 18  Demonstration of bottom-up and top-down processing Experiment by Stephen Palmer (1975): Effect of context on perception – Speeded object-recognition task: – e.g. kitchen scene, then shown bread, mailbox, drum 19  Demonstration of bottom-up and top-down processing Palmer’s experiment – Context-congruent objects: 80% recognition – Context-incongruent object: 40% recognition - Shows how a person’s knowledge of a particular context provided by a scene can influence (or inhibit!) perception 20 Bottom Up Processing 21  Bottom-up processing The first step in perceptual process Analysing objects into smaller components (features) – Feature approach to object perception Two theories – Feature Integration Theory (FIT) – Recognition by Components approach (RBC) 22  Bottom-up processing: Feature approach to object perception Basic idea – We break down and analyse objects according to features before we put them together and synthesise them to recognise what objects they are – Analysis before synthesis A model for recognising letters/ alphabets Example, you are shown the letter ‘A’ 23  Bottom-up processing: A model for recognising letters A model for recognizing letters by analyzing their features. The stimulus, A, activates three feature-units. These feature-units cause strong activation of the A letter-unit and weaker activation of units for letters such as the N and the O, which lack some of A’s features. The A is identified by the high level of activation of the A letter-unit. 24 Bottom-up processing: A model for recognising letters 2 stages Letter Analysis Stage Feature Analysis Our mental bank consist of letter Stage units Our mental bank Each letter unit receives input from consist of feature the feature units associated with that units letter Each unit respond ‘A’ unit receives input from three to specific features feature units ‘A’ activates three Other letters that have common units: features with A also receive input from feature units that are activated by ‘A’ (eg. ‘A’, ‘N’, ‘T’) BUT only ‘A’ is recognised due to a higher level of activation 25  Bottom-up processing: A model for recognising letters Basic idea in feature analysis: – Activation of letter units provide the information to determine which letter is present – Our visual system just needs to determine which unit is activated most strongly – Advantage of feature analysis: detect shared features even when letters look different – Eg. – But the model would have difficulty with: 26  Evidence for Feature Analysis Ann Treisman (1986)’s Visual Search Experiment – Wants to find out how fast can people find a target based on how many distractors are present? – Eg. Find the ‘O’ among the ‘V’s Easy to find the ‘O’ as it “pops out” Even when there are many distractors 27  More Evidence for Feature Analysis – Eg. Find the ‘R’ among the ‘P’s and ‘Q’s Difficult to find the ‘R’ Does not “pop out” Takes a longer time when there are more distractors Shared features prevent “pop up” effect. - What are the shared features? 28 More Evidence for Feature Analysis Standard result for Visual Search experiment Differences in results because of features of the target letter and distractor letter Results of visual search experiments like the one in the demonstration. (a) Target = 0; Distractors = V; (b) Target = R; Distractors = P and Q. (Based on Treisman, 1986) 29 Permainan: Cuba cari Waldo 30 31  1) Feature Integration Theory (FIT) Proposed by Treisman (1986) => Free floating features => Object Flow diagram for Treisman’s (1986) feature integration theory. According to this theory, objects are first analyzed into features in the preattentive stage, and then these features are combined into an object that can be perceived in the focused attention stage. 32  Evidence for FIT: Illusory Conjuctions “Illusory” - misleading Treisman & Schmidt (1982) Figure 3.18 (p. 68) Stimuli for Treisman and Schmidt’s (1982) illusory conjunction experiment. The geometrical figures were different colors, as indicated by the key. The numbers were black. 33 Evidence for FIT: Illusory Conjuctions Participants in the experiment shown Figure 3.18 for 20miliseconds Participants reported seeing “small red circle”, “small green triangle” Illusory Conjuctions – incorrect combination of features from two different stimulus Reason : – At the Preattentive stage-Components of perception exist independently of one another 34  Evidence for FIT: Illusory Conjuctions Features like ‘color’, ‘curvature’, ‘angle’ are free floating The results of the illusory conjunction experiment suggest that very early in the perceptual process, features that make up an object are “free floating.” This is symbolized here by showing some of the features of a cell phone as existing separately from one another at the beginning of the perceptual process. 35 Evidence for FIT: Illusory Conjuctions Role of attention: Focus on shapes can eliminate illusory conjunctions – Eg. Participants were told to only focus on the objects and ignore the numbers – so all shapes were paired with their correct colors Role of knowledge: Top-down processing can channel perception – Eg participants told they will be looking at carrot, a lake and a tire, they were more likely to correctly identify the object and its colour Three stimuli used by Treisman to illustrate how top-down processing can influence the combining of features 36  2) Recognition By Components (RBC) Biederman (1987): The basic component of perception are 36 geons (3D- shapes/volumes) Geons – features are not lines, curves or colors. 37 - e.g cylinders, pyramid, rectangular solids shapes 2) Recognition By Components (RBC) Three properties: – View invariances – Discriminability – Resistance to visual noise View invariances (can be identified when view from diff. angles ) – Occurs because geons have view invariant properties 38  2) Recognition By Components (RBC) Discriminability – Each geon can be differentiated from others from all viewpoints (e.g cylinder vs. rectangular) Resistance to visual noise – Each geon can be identified even in noisy conditions – But when geons cannot be identified, we cannot recognise the object – (e.g pg 72) 39  2) Recognition By Components (RBC) Conclusion from the RBC theory: If enough information is available for us to identify an object’s basic geons, we will be able to identify the object We can recognise objects based on a small number of basic shapes 40  FIT vs RBC Both agree on the idea of early analysis of objects into parts (in the early part of the perception process) FIT – focus on basic features (lines, curves, colours) & the role of attention in combining them RBC – focus on how we perceive 3 dimensional shapes (geons) 41 Top Down Processing 42  Top-down Processing What do you see in the picture? 43  Top-down Processing How is the environment organised into objects – The concept of Perceptual organisation - the organisation of elements of the environments into objects Perceptual organisation - Studied by Gestalt Psychologists Gestalt- German word for “form” The essential point in gestalt is that in perception, the whole is different from the sum of its parts. During perception, the mind groups patterns according to rules they called the laws of perceptual organization 44  The Gestalt Approach Perception is due to laws of perceptual organisation – 6 laws 1. Law of Pragnanz (good form) 2. Law of Similarity 3. Law of Good Continuation 4. Law of Proximity (or nearness) 5. Law of Common fate 6. Law of Familiarity Additional Laws: 7. Law of Closure 8. Law of Figure/Ground 45  Gestalt Principles: Laws of Perceptual Organisation 1. Pragnanz / simplicity / good figure - A stimulus will be organized into as good a figure as possible Good = symmetrical, simple, and regular Example 1: The above figure appears to the eye as a square overlapping triangle, not a combination of several shapes Example 2: 46  Gestalt Principles: Laws of Perceptual Organisation 2. Similarity: similar things are grouped together – Elements that look similar will be perceived as part of the same form. Example 1: There seems to be a triangle in the square. Example 2: 47 Gestalt Principles: Laws of Perceptual Organisation Example 3: Grouping (due to similarity) 48  Laws of Perceptual Organisation 3. Good continuation – connected points form a straight or smooth curving line Example 1: People tend to draw a good continuous line. Points which, when connected, result in straight or smoothly curving lines, are seen as belonging together, and the lined tend to be seen as following the smoothest. 49 Laws of Perceptual Organisation -Good continuation Example 2: 50  Laws of Perceptual Organisation 4. Proximity or nearness – things that are closer together will be perceived as grouped together On the left, there appears to be three horizontal rows, while on the right, the grouping appears to be columns. 51  Laws of Perceptual Organisation 5.Common Fate – Things moving together in the same direction are grouped together 52  Laws of Perceptual Organisation 6. Familiarity – things can be grouped if the group appear familiar or meaningful – Eg. Look at the next picture and see if you can find all 12 human faces 53 Finding faces in a landscape 54 Laws of Perceptual Organisation 55  Laws of Perceptual Organisation Some Additional laws of perceptual Organisation (not in the textbook) 7. Closure - Humans tend to close up a space to complete a contour (ignore gaps in the figure) 56  Laws of Perceptual Organisation 8. Figure/Ground - A stimulus will be perceived as separate from it's ground 57  Summary Be sure you know: how does perception happen? What is the difference between bottom up & top down processing? What do we mean by feature analysis? What does the FIT theory say? – What is the pop out effect? – What does illusory conjunction mean? What does the RBC theory say? What is the difference between the FIT & RBC theory? What are the Gestalt perceptual laws? How do these laws influence our perception? 58  Happy Reading & Teruskan Membuat Assignment Bye! 59