Lecture 2 – Perception PDF

Lecture 2 – Perception 1  Content 1. What is Sensation and Perception? 2. Perception 3. Bottom-up Processing Part I 4. Top-Down Processing 5. Objection Perception 6. Face Perception 7. Neural Pathway of Perception...

Lecture 2 – Perception 1  Content 1. What is Sensation and Perception? 2. Perception 3. Bottom-up Processing Part I 4. Top-Down Processing 5. Objection Perception 6. Face Perception 7. Neural Pathway of Perception Part II 8. Deficits of Perception 2  Part I – Content 1. What is Sensation and Perception? 2. Perception 3. Bottom-up Processing 4. Top-Down Processing 3  Sensation vs. Perception What do you see? – Sensation: Five senses: vision, hearing, taste, smell, touch The detection of external stimuli and the transmission of this information to the brain Happens at the sensory organs What is this? No senses no perception – Perception: Experiences resulting from the stimulation of the senses Happens at the brain --- The processing, organization, and interpretation of sensory signals 4  How much do you know? Sense Sensory Organ Vision Eye (retina) Eye (retina) Hearing Ear (inner ear) Ear (inner ear) Taste Tongue (taste buds) Tongue (taste buds) Smell Nose (upper nostrils) Nose (Upper nostrils) Touch Skin Skin A simple overview 6  Diagram depicting the primary sensory areas of the Understand the function, e.g which past processing what function? human brain FIGURE 5.10 Primary Sensory Areas These are the primary brain regions where information about vision, hearing, taste, smell, and touch are projected.  From Sensation Diagram demonstrating an to Perception example of sensory input being (Can be Physical / Chemical) transferred to perception Occipital lobe  Sensory Information is Translated into Meaningful Signals Sensory coding: Sensory receptors translate the physical properties of stimuli into patterns of neural impulses. Transduction: the process by which sensory stimuli are converted to signals the brain can interpret – The brain needs qualitative and quantitative information about a stimulus. Qualitative information consists of the most basic qualities of a stimulus. Quantitative information consists of the degree, or 巨⼤ magnitude. Diagram contrasting qualitative and quantitative sensory information  Part I – Content 1. What is Sensation and Perception? 2. Perception 3. Bottom-up Processing 4. Top-Down Processing 11  Perception Perception: – Experiences resulting from the stimulation of the senses – Perception is built on a foundation of information from the environment. – Then, in what ways do we make use of the environment? 12  Fundamental Processing of Human Perception Bottom-up processing Top-down processing Perceptual processing begins at Perceptual processing begins at the receptors of the sensory the brain (Top of the perceptual organs (Bottom of the perceptual system) system) to the brain (Top of the Prior knowledge in combination perceptual system) with relatively simple and Perception occurs simply and ambiguous information from the directly. There is little need for sensory receptors. complex information processing. (Indirect) Constructive perception approach Direct perception approach 13  Part I – Content 1. What is Sensation and Perception? 2. Perception 3. Bottom-up Processing 4. Top-Down Processing 14  Fundamental Processing of Human Perception Bottom-up processing – Parts are identified, put together, and then recognition occurs – Data-driven or Stimulus-driven Perception – Base on features – Direct perception approach 15  Bottom-up Processing Theories 1 Direct perception theory (Gibson, 1966) 2 Template theories 3 Feature-matching theories 4 Recognition-by-components theory (Bidderman, 1987) 16  Gibson’s Theory of Direct Perception (1966) Eleanor J. Gibson The information in our sensory receptors is all we need to perceive anything – Do not need the aid of complex thought processes to explain perception  Ecological perception For example, we use texture gradients as cues for depth and distance – Allows us to perceive directly the relative proximity or distance of objects 17  C Which rock is the closest to you? Based on detail of rock and scaleof rock B A 18  Depth Perception in Infants (Gibson and Walk, 1960) extracted from Gerrig (2012) Gibson and Walk’s Visual Cliff Experiment: The Classic Footage: https://www.youtube.com/watch?v=3WvtEFJGp-8 A new version: https://youtu.be/p6cqNhHrMJA?t=31 (Up to 1:08) Studies by Karen Adolph revealing that infants’ performance is not due to fear of heights: 19 https://www.youtube.com/watch?v=WanGt1G6ScA  Template Theories Features only Basics of template theories – Multiple templates are held in memory – To recognize the incoming stimulus, you compare it to templates in memory until a match is found See stimuli Search memory for a match 20 extracted from Sternberg & Sternberg (2012)  Template Theories Weakness of theory – Problem of imperfect matches – Cannot account for the flexibility of pattern recognition system See stimuli Search for match in memory  No perfect match in memory 21 extracted from Sternberg & Sternberg (2012)  Feature-Matching Theories perception Have to connect with behaviral expriences Recognize objects on the basis of a small number of characteristics (features) – Features: line, orientation, curve, color, etc – Detect specific elements and assemble them into more complex forms – Brain cells that respond to specific features such as lines and angles are referred to as “feature detectors” Hubel and Wiesel (1964) 22 extracted from Sternberg & Sternberg (2012)  Recognition-by-Components (RBC) Theory Argued that previous theory only interpret 2D Irving Biederman (1987) Describes how 3D images are identified Breaks objects down into geons (geometric ions) We quickly recognize objects by observing the edges of the objects and then decomposing the objects into geons. Geons can be recomposed into alternative arrangements 23 extracted from Sternberg & Sternberg (2012) Recognition-by-Components (RBC) Theory (Biederman, 1987) Geon 3 + Geon 5 Rearrange 24 Recognition-by-Components (RBC) Theory No matter viewpoint you also can recognise that is chair (object) Geons: simple and viewpoint-invariant 25  Recognition-by-Components (RBC) Theory Geons: simple and viewpoint-invariant Problem: – Does not explain how do we recognize or distinguish specific items given they all built from the same set of geons – e.g., my face versus your face, while we share the same geons 26  Part I – Content 1. What is Sensation and Perception? 2. Perception 3. Bottom-up Processing They are working together 4. Top-Down Processing 27  Fundamental Processing of Human Perception Top-down processing – People actively construct perceptions using information based on existing knowledge and expectations Lack of the full picture – Driven by high-level cognitive processes – Constructive perception approach – Perceiver builds (constructs) a cognitive understanding (perception) of a stimulus based on prior knowledge, experience, expectation and making inferences. 28  Fundamental Processing of Human Perception Top-down processing – It enables people to rapidly identify objects and scenes if it is within their expectations Palmer (1975): The effects of contextual scenes on the identification of objects 29 30 Figure 1.13 Stimuli used in Palmer’s (1975) experiment. The scene at the left is presented first, and then one of the objects on the right is briefly flashed. The subject's task is to name the object and rate his confidence in his response. Participants in this experiment were more accurate in identifying the bread (Picture A). This indicates that their knowledge of what is 31 usually found in kitchens influenced their performance.  Fundamental Processing of Human Perception Top-down processing – It enables people to rapidly identify objects and scenes if it is within their expectations – With expectation, we may “see” things that aren’t there or change our interpretation of things. 32 33  What makes top-down processing possible? Context effects Semantic regularities 34  What makes top-down processing possible? Context effects The surrounding environment influences our perception BAT Figure 3.11 “Multiple personalities of a blob.” What we expect to see in different contexts influences our interpretation of the identity of the “blob” 36 inside the circles.  Semantic Regularities Semantics: – In language: the meanings of words or sentences – In perception: the meanings of scenes Semantic regularities are the characteristics associated with functions carried out in different types of scenes. 37  Semantic Regularities Scene schema: – The knowledge of what a given scene typically contains. – The expectations created by scene schemas contribute to our ability to perceive objects and scenes 38  Content 1. What is Sensation and Perception? 2. Perception 3. Bottom-up Processing Part I 4. Top-Down Processing 5. Objection Perception 6. Face Perception 7. Neural Pathway of Perception Part II 8. Deficits of Perception 39  Part II – Content 1. Objection Perception 2. Face Perception 3. Neural Pathway of Perception 4. Deficits of Perception 40  Theories of Object Perception Bottom-Up processing: – Gestalt Principles of Organization Top-down Processing: – Theory of Unconscious Inference 41  Theories of Object Perception Bottom-Up processing: – Gestalt Principles of Organization Top-down Processing: – Theory of Unconscious Inference 42  Gestalt Principles of Organization Originated by a group of psychologists, called Gestalt Psychologists in the 19th century “Old” view of perception —structuralism – Perception involves adding up sensations – Gestalt psychologists rejected this structuralism view as it cannot explain perception in reality Figure 3.15 According to structuralism, a number of sensations (represented by the dots) add up to create our perception of the face. 43  Gestalt Principles of Organization The German word Gestalt means “shape” or “form.” As used in psychology, Gestalt means “organized whole.” Gestalt Principles: The mind groups patterns according to intrinsic laws of perceptual organization Gestalt psychology postulated a series of laws to explain how our brains group the perceived features of a visual scene into organized wholes. Making use of the bottom-up approach 44  Gestalt Principles of Organization Basic tenet – “The whole is more than a sum of its parts” Law of Prägnanz – Individuals organize their experience in as simple, concise, symmetrical, and complete manner as possible Six principles that aid in fast recognition of objects 45  Gestalt Principles of Organization Figure-ground – Organize perceptions by distinguishing between a figure and a background Proximity – Elements tend to be grouped together according to their nearness Similarity – Items similar in some respect tend to be grouped together 46 extracted from Sternberg & Sternberg (2012) 47  Gestalt Principles of Organization Continuity Based on smooth continuity, which is preferred to abrupt changes of direction Closure Items are grouped together if they tend to complete a figure Symmetry Prefer to perceive objects as mirror images 48 extracted from Sternberg & Sternberg (2012)  FIGURE 5.21 Good Continuation (a) We tend to interpret intersecting lines as continuous. Here, as a result, the bar appears to be completely behind the occluder. (b) In this drawing by the vision scientist Peter Tse, two cats appear to be Figure 3.18 (a) Rope on the beach. (b) Good continuation one extremely long cat wrapped around the helps us perceive the rope as a single strand pole. Yet no continuous contours permit this completion, and we know a cat is unlikely to 49 be so long.  50 extracted from Sternberg & Sternberg (2012)  Theories of Object Perception Bottom-Up processing: – Gestalt Principles of Organization Top-down Processing: – Theory of Unconscious Inference 51  Theory of Unconscious Inference Top-down theory Some perceptions are the results of unconscious assumptions we make about the environment – We use our knowledge to inform our perceptions We infer much of what we know about the world Likelihood principle – We perceive the world in the way that is “most likely” based on our past experiences 52  Theory of Unconscious Inference Proposed by Hermann von Helmholtz (1821-1894) Figure 3.14 The display in (a) is usually interpreted as being (b) a blue rectangle in front of a red rectangle. It could, however, be (c) a blue rectangle and an appropriately positioned six-sided red figure. 53  Part II – Content 1. Objection Perception 2. Face Perception 3. Neural Pathway of Perception 4. Deficits of Perception 54  Pattern Recognition Systems Martha Farah (1992, 1995; Farah et al., 1998) 1. Configurational system – Recognize larger configurations; recognizing human face as a whole – Especially for recognizing face – Problem? 2. Feature analysis system – Recognize parts of objects; feature by feature – Assemble parts into wholes – Problem? 55  Pattern Recognition Systems Most of the time, we use the configurational system. Yet, we do use the feature analysis system in recognizing face…unfamiliar face! For faces that are unfamiliar, we may need to analyze the individual features and then put all features to aid recognition Imagine that you bump into an old friend whom you haven’t met for 10 years. In sum, both configurational and feature analysis systems may help in making difficult recognitions and discriminations on recognizing human faces. 56  Fusiform Gyrus in Temporal Lobe Implicated in pattern recognition Studies illustrate it is active in facial recognition – Fusiform Face Area (FFA) However, also active if high expertise in any item (birds, cars) recognition – Expert individuation hypothesis Recently, it has been implicated in processing facial emotions (Ganel et al., 2005) 57  Part II – Content 1. Objection Perception 2. Face Perception 3. Neural Pathway of Perception 4. Deficits of Perception 58  Neurons and Perception Some neurons respond best to things that occur regularly in the environment. Neurons become tuned to respond best to what we commonly experience. 1. Horizontals and verticals 2. “Feature detectors” cells Hubel and Wiesel (1964) Hubel, D. H., and Wiesel, T.N., "Effects of monocular deprivation in kittens." Naunyn- Schmiedebergs Archiv for Experimentelle Pathologie und Pharmakologie 248 (1964): 59 492–7.  Neurons and Perception Some neurons respond best to things that occur regularly in the environment. Neurons become tuned to respond best to what we commonly experience. 3. Experience-dependent plasticity Figure 3.27 (a) Greeble stimuli used by Gauthier. Participants were trained to name each different Greeble. (b) Magnitude of FFA responses to faces and Greebles before and after Greeble training. 60  Neurons and Perception Figure 3.27 (a) Greeble stimuli used by Gauthier. Participants were trained to name each different Greeble. (b) Magnitude of FFA responses to faces and Greebles before and after Greeble training. 61  Visual Pathways in the Brain The Where/What Pathway (Ungerleider & Mishkin, 1982) “Where” Pathway - Indicates spatial location. - Dorsal pathway: Occipital to Parietal lobes - Responsible for processing location “What” Pathway and motion - Indicates object identity. information. -Ventral pathway: Occipital to Temporal lobes - Responsible for processing color, shape, and identity of visual stimuli 62  Visual Pathways in the Brain The Where/What Pathway (Ungerleider & Mishkin, 1982) Figure 3.30 The two types of discrimination tasks used by Ungerleider and Mishkin. (a) Object discrimination: Pick the correct shape. Lesioning the temporal lobe (purple-shaded area) makes this task difficult. (b) Landmark discrimination: Pick the food well closer to the cylinder. Lesioning the parietal lobe makes this task difficult. 63  Visual Pathways in the Brain The What/How Hypothesis (Milner & Goodale, 2008) - Where something is located in space “How” Pathway - Indicates spatial location. - Dorsal pathway: Occipital to Parietal lobes - Responsible for controlling “What” Pathway movements: How can - Indicates object identity. we situate ourselves -Ventral pathway: Occipital to Temporal lobes to grasp the object - Responsible for processing color, shape, and identified by the identity of visual stimuli “What” Pathway. 64  Part II – Content 1. Objection Perception 2. Face Perception 3. Neural Pathway of Perception 4. Deficits of Perception (a recap of what we have learned in Biopsy) 65  Deficits in Perception Agnosia – People who suffer from visual-object agnosia can see all parts of the visual field, but the objects they see do not mean anything to them (Kolb & Whishaw, 1985) – Disruption of the “what” pathway – Caused by damage to the border of the temporal and occipital lobes or restricted oxygen flow to areas of the brain (due to traumatic brain injury) 66  Deficits in Perception Prosopagnosia – Inability to recognize faces (even one’s own face) after brain damage – Can see the face of another person and even recognize the facial emotion expressions – However, the patients failed to recognize the identity of the person (Is this a mother? A friend? A stranger?) – Especially related to the damage of the right fusiform gyrus – Ability to recognize objects is intact – Disruption of the “what” pathway on face An illustration of prosopagnosia by Dr. Oliver Sacks 67 https://youtu.be/k5bvnXYIQG8 and https://youtu.be/664vzbwkc0M  Deficits in Perception Simultagnosia – Object blindness – Perceives only one stimulus at a time—single word or object – Disruption of the “what” pathway 68  Deficits in Perception Optic ataxia – Cannot use vision to guide movement – Unable to reach for items – Disruption of the “how” pathway – Result from a processing failure in the posterior parietal cortex, where sensorimotor information is processed 69  Deficits in Color Perception Color blindness Trichromacy (Trichromats): normal color vision Sex-linked genetic defect on the x-chromosome More common in men than in women 70  Color Vision Trichromatic Theory Human eye has three types of receptors sensitive to the specific wavelengths associated with red, green, and blue-violet White is formed when the three primary colors of light are combined 71  Deficits in Color Perception Rod monochromacy (achromacy): Monochromats No color vision at all With nonfunctional cone cells See through rod cells  shades of gray Rare (1 in 40,000 people) 72  Deficits in Color Perception Dichromacy: Dichromats Only two of the mechanisms for color perception work (red, green and blue-violet), and one is malfunctioning 8% in male; 1% in female Red-green color blindness: – most common – Have difficulty distinguishing red from green  In summary… Source: 74 https://www.simplypsychology.org/perception-theories.html