Perception

What you want to remember Perception is more than photons and pressure. Perception is divided from cognition/emotion but they are often intertwined. Perception follows laws and heuristics. 2

Sensation - the registration of physical stimuli Hearing - anatomy and function of the ear Vision - anatomy and function of the eye 3

What is the purpose of sensory processing? Sensation What is the purpose of sensory processing? To transform physical stimuli in the environment into neural signals in the brain Example (Hearing): Sound waves are transformed into vibrations in the ear, and the strength of those vibrations are coded by sensory neurons 4

Some 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? 5

Some Questions of Interest What are two fundamental approaches to explaining perception? What happens when people with normal visual sensations cannot perceive visual stimuli? 6

Perception Is… The process of recognizing, organizing, and interpreting information How do you recognize these items? 7

Basic Concepts (Gibson) Distal object Grandma’s face Informational medium Reflected light from Grandma’s face Proximal stimulation Photon absorption in the rod and cone cells of the retina Perceptual object 8

Perceptual Basics Sensory adaptation Our senses respond to change Occurs when sensory receptors change their sensitivity to the stimulus Constant stimulation leads to lower sensitivity Our senses respond to change Perceptual training 9

Perceptual Illusions Sometimes we cannot perceive what does exist Sometimes we perceive things that do not exist 10

Perceptual Illusions Sometimes we perceive what cannot be there 11

http://www.vimm.it/cochlea/cochleapages/overview/history.htm 12

Figure 7.4 Figure 7.4 The basilar membrane of the human cochlea. High-frequency sounds produce their maximum displacement near the base. Low-frequency sounds produce their maximum displacement near the apex. 13

Auditory Cortex Tonotopic organization in superior temporal lobe Corresponds to apex of cochlea Corresponds to base of cochlea Primary auditory cortex Secondary auditory cortex Tonotopic organization in superior temporal lobe 14

Typical human range about 20 - 20 kHz Audiograms for various species 15

Our Visual System Light travels through the eye and focuses on the retina Electromagnetic light energy is converted into neural electrochemical impulses 16

Our Visual System Three main layers of neural tissue in retina Ganglion cells Amacrine cells, horizontal cells, bipolar cells Photoreceptors Rods and cones 17

Visual Pathways in the Brain What/where hypothesis One path for identifying Temporal lobe lesions in monkeys Can indicate where but not what Another for spatially locating Parietal lobe lesions in monkeys Can indicate what but not where 18

Theories of Perception Bottom-up theories Parts are identified, put together, and then recognition occurs Top-down theories People actively construct perceptions using information based on expectations 19

Bottom-Up Processing Theories Bottom-Up Processing Theories Direct perception Template theories Feature-matching theories Recognition-by-components theory 20

Template Theories Basics of template theories Template Theories Basics of template theories Multiple templates are held in memory To recognize the incoming stimuli, you compare to templates in memory until a match is found Search memory for a match See stimuli 21

Template Theories Weakness of theory Problem of imperfect matches Template Theories Weakness of theory Problem of imperfect matches Cannot account for the flexibility of pattern recognition system Search for match in memory See stimuli No perfect match in memory 22

Feature-Matching Theories Feature-Matching Theories Recognize objects on the basis of a small number of characteristics (features) 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” 23

Pandemonium Model Four kinds of demons Image demons Feature demons Cognitive demons Decision demons 24

Physiological Evidence for Features Physiological Evidence for Features Hubel & Wiesel (1979) Simple cells detect bars or edges of particular orientation in particular location Complex cells detect bars or edges of particular orientation, exact location abstracted Hypercomplex cells detect particular colors (simple and complex cells), bars, or edges of particular length or moving in a particular direction 25

Recognition-by-Components (RBC) Theory Recognition-by-Components (RBC) Theory Biederman (1987) Describes how 3D images are identified Breaks objects down into geons Objects are identified by geons, relationship between them 26

Gibson’s Theory of Direct Perception (Ecological psych) 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 27

Gibson’s Theory of Direct Perception (Ecological psych) Use texture gradients as cues for depth and distance Allows us to perceive directly the relative proximity or distance of objects 28

Top-Down Processing (Constructive Approach) Top-Down Processing (Constructive Approach) Perception is not automatic from raw stimuli Processing is needed to build perception Top-down processing occurs quickly and involves making inferences, guessing from experience, and basing one perception on another 29

Evidence for Top-Down Processing Evidence for Top-Down Processing Context effects 30

Configural-Superiority Effect Objects presented in context are easier to recognize than objects presented alone Task: Spot the different stimuli, press button 31

Configural-Superiority Effect Target Composite Measure reaction time Target alone = 1884 Composite = 749 Target spotted faster in a context! 32

Which Approach Is Right? Top-down or bottom-up Perhaps a bit of both 33

Beginning of Gestalt psychology 1910 – Max Wertheimer on vacation noticed that distal objects seemed to move with the train; nearby objects went past. Why? Study of apparent motion – why stationary objects appear to move 34

Apparent motion Phi phenomenon – flashing a vertical light that is followed 50-60 msec later by a horizontal light produces the appearance of movement. The light appears to move from vertical to horizontal Movement only perceived if delay was 50 – 60 msec The perceptual experience had properties the individual components did not 1st Gestalt paper presented in 1912 35

Basic premise of Gestalt psychology Humans are not passive receivers of sensory information. Our perceptions are active, lively, and organized We actively organize perceptions into coherent wholes – today the process is referred to as top-down or conceptually driven processing 36

Scientific Method They emphasized the physical environment. Gestalt perspectives on scientific method reflect their acceptance of field physics as a model for psychology. They emphasized the physical environment. They used experience to guide analysis in psychology. They started research with phenomenological investigation. They accepted a broad range of methods in psychology. 37

Mind and Brain Gestalt perspectives on mind and brain reject reductionistic and linear models of mind. Köhler argued for models of mind based in natural systems. He used models of mind based in the brain. He described models in terms of free dynamics. Köhler advocated isomorphism (ex. psychophysical isomorphism). There is a structural correspondence between experience and underlying brain processes. 38

Geographical environment – the physical world Key terms in gestalt psychology: Geographical versus behavioral environment Geographical environment – the physical world Behavioral environment – our interpretation of the physical world Our interpretation or organization can produce a behavioral world that is very different from the physical world Illusions, dreaming, fantasies 39

Gestalt’s View of Perception 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 40

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Perception is not just detection Perception is not just about detecting color or shape. Perception is about organizing visual information. How do we organize visual information? 43

Müller-Lyer-illusion Ponzo illusion 44

Or when do we fail to organize visual information? 45

Gestalt’s Principles of Visual Perception 46

Closure 47

Gestalt’s Principles of Visual Perception 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 48

The figure represents “some thing.” The contours belong to the figure rather than to the ground. 49

Which one if the figure and which is the ground? This is easy. The figure tends to have solid and continuous surface. 50

Gestalt’s Principles of Visual Perception B 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 A D C

Rules for Linking Contours Good continuation: group elements to form smoothly continuing lines 53

The Relatability Principle 54

Non-accidental features provide clues to object structure Meaning in the Edges Non-accidental features provide clues to object structure 55

Is the Whole Seen Before the Parts? Global superiority effect (Navon, 1977) 56

Complex listening: several concurrent sound sources Auditory scene analysis “cocktail-party effect”

Stream segregation

Continuity

Grouping by similarity

Tactile illusions 61

Depth Perception The ability to see the world in three dimensions and detect distance Vision only has a two-dimensional view We must interpret the information given to perceive depth We take flat images and create a three- dimensional view Optical illusions demonstrate that this interpretation does not always have to be correct 62

Monocular Depth Cues Texture gradients Relative size Interposition Grain of item Relative size Bigger is closer Interposition Closer are in front of other objects 63

Monocular Depth Cues Linear perspective Aerial perspective Parallel lines converge in distance Aerial perspective Images seem blurry farther away Motion parallax Objects get smaller at decreasing speed in distance 64

Binocular Depth Cues Binocular convergence Binocular disparity Eyes turn inward as object moves toward you; brain uses this information to judge distance Binocular disparity Each eye views a slightly different angle of an object; brain uses this to create a 3D image 65

Agnosias, Ataxias, & Cognition Demonstrate the modularity of cognition Help us to understand what brain locations are associated with different types of higher-level processing Provide us with a model of how normal processing must work 66

Deficits in Perception Disruption of the “what” pathway Inability to recognize and identify objects or people, despite having knowledge of the characteristics of the objects or people Disruption of the “how” pathway Cannot use vision to guide movement Unable to reach for items

Fusiform Gyrus in Temporal Lobe Implicated in pattern recognition Studies illustrate it is active in facial recognition However, also active if high expertise in any item (birds, cars) recognition Expert individuation hypothesis 68

Evidence for Separate Systems Prosopagnosia Inability to recognize faces after brain damage Ability to recognize objects is intact Associative agnosia Difficulty with recognizing objects Can recognize faces 69

Psychophysics the measurement of sensory experiences Webers Law Δφ = cφ φ = Stimuli Fechners Law Ψ = log φ Ψ = Sensation magnitude 70

Perception or Attention Movement patterns / reflexes What cannot be unseen / heard Pop-out effect Change blindness 71

What you want to remember Perception is more than photons and pressure. Perception is divided from cognition/emotion but they are often intertwined. Perception follows laws and heuristics. 72