THE STUDY OF PERCEPTION

1. THE STUDY OF PERCEPTION Anthony J Greene

2. Chapter 1 Outline • Why study perception? • Perception is reality • How we percieve. • Historical Approaches • Scientific Study of Perception:The Scientific Revolution: Hypothesis, Data & Theory • FunctionalismThe problem of Perception: • Psychophysics • Evolution • Structuralism • Neuroscience Anthony J Greene

3. Why Study Perception? • What we get from perception • Perception is our only source of information: we have no knowledge, or experience except through perception • Perception allows survival • The utility of perceptual systems informs us about why they evolved Anthony J Greene

4. The way we perceive • Perceptual systems are incredible–Nothing man-made is even close • The mechanisms of perceptual systems inform us about how they evolved • Sensory enhancement (glasses, hearing aids), • Sensory substitution Anthony J Greene

5. A Song of Ourselves • Perception is not always veridical • What we are able to perceive • We are fundamentally perceptual beings • Thought, memory and experience are perceptual (either directly or indirectly) • Art, Music, Food, Physical Sensations etc. Anthony J Greene

6. Lemon A man makes a picture A moving picture. Through the light projected He can see himself up close. Man captures color, Man likes to stare, He turns his money into light To look for her; She is the dreamer, She's imagination. --U2 Anthony J Greene

7. Philosophical & Historical Approaches to Perception Realism Subjectivism-e.g. Democritus, Plato Dualism-e.g. Descartes Materialism-e.g. Bacon Nativism-e.g. Plato Empiricism-e.g. Socrates Anthony J Greene

8. Science Derived from the Philosophies of Empiricism & Materialism– Fact & Theory Anthony J Greene

9. Fact & Theory • Facts must be observable (data) • Theory = understanding • Theory is not hypothetical • Theory is broad, fact and hypothesis are narrow • Theories must be consistent with all available (relevant) facts • Theory guides the search for fact • Facts are only important if they inform theory • Theory is more important than fact • The progress of theory is the purpose of science Anthony J Greene

10. The Advancement of Theory Anthony J Greene

11. Scientific Approaches to perception Functionalism (purposes of perception) • Evolution • Psychopohysics Structuralism (mechanisms of perception) • Neuroscience Anthony J Greene

12. Perceptual Systems Vision • Object Identification/recognition • Spatial Vision: Navigation & Motion Perception Audition • Object Identification/recognition • Object Localization Touch • Object Identification/recognition • Pain (detection of tissue damage) • Proprioception Gustation & Olefaction • Chemical detection and identification • Nutrition & and poison avoidance Anthony J Greene

13. Problem of Perception 1 Cornea 2 Lens 3 Retina 4 Optic Nerve 5 Brain Anthony J Greene

14. Proximal vs. Distal Stimulation Proximal Stimulus is upside down • The brain is not looking at retinal pictures Proximal stimulus is 2 dimensional (Depth Perception) • 3rd dimension is lost from distal to proximal, however we perceive in 3 dimensions • How does then do we experience a 3rd dimension? Anthony J Greene

15. Perceptual Experience Mirrors Distal Stimulation 1 Size Constancy 2 Shape Constancy 3 Position Constancy 4 Brightness Constancy 5 Color Constancy Anthony J Greene

16. Size Constancy Anthony J Greene

17. Size Constancy If object moves 2x further away, the retinal image decreases by a factor of 2, but we do not perceive it to shrink Anthony J Greene

18. Shape Constancy Anthony J Greene

19. Position Constancy Anthony J Greene

20. Brightness Constancy A light meter would read that the right side of the panel is white and that the left side is gray Visual systems interpret them both as white Anthony J Greene

21. Color Constancy • Under different ambient lighting conditions, the mondrian will reflect different frequencies (as measured by a light meter). e.g. green light reflected off a red surface would be read by a light meter as orange or yellow Anthony J Greene

22. Brightness Constancy • Visual systems compensate for ambient lighting, so that under almost all conditions the colors appear stable • There are instances when there does not exist a correspondence between distal image and perception (illusions and ambiguity) Anthony J Greene

23. Illusions • Cases where our perceptual experience is inaccurate • How does the brain get tricked? Anthony J Greene

24. Illusions Anthony J Greene

25. Anthony J Greene

26. Perceptual Ambiguity One proximal stimulus produces many perceptual experiences Perceptual experience is not just a function of what hits the eye The man bent over his guitar Anthony J Greene

27. The Man With The Blue Guitar A shearsman of sorts. The day was green. They said, "You have a blue guitar, You do not play things as they are." The man replied, "Things as they are Are changed upon the blue guitar." And they said then, "But play, you must, A tune beyond us, yet ourselves, A tune upon the blue guitar Of things exactly as they are." --Wallace Stevens. Anthony J Greene

28. Psychophysics • Psychophysics: The science of defining quantitative relationships between physical and psychological (subjective) events • Fechner (1801–1887) invented psychophysics, thought to be the true founder of experimental psychology • Pioneering work relating changes in the physical world to changes in our psychological experiences Anthony J Greene

29. Psychophysics (cont’d) • Weber (1795–1878) discovered that the smallest change in a stimulus, such as the weight of an object, that can be detected is a constant proportion of the stimulus level: “Weber’s Law” Anthony J Greene

30. Psychophysics (cont’d) • JND (Just Noticeable Difference): The smallest detectable difference between two stimuli, or the minimum change in a stimulus that can be correctly judged as different from a reference stimulus. Also known as difference threshold • Two-point threshold: The minimum distance at which two stimuli (e.g., two simultaneous touches) can be distinguished Anthony J Greene

31. Psychophysics (cont’d) Fechner’s Law:Relationship between stimulus magnitude and resulting sensation magnitude is exponential. Anthony J Greene

32. Psychophysics (cont’d) Stevens’ Power Law: Relationship between stimulus magnitude and resulting sensation magnitude. Exponent can be positive, zero, or negative. Anthony J Greene

33. Some species sense energies that humans cannot: Bees see ultraviolet lights Rattlesnakes sense infrared energy Dogs and cats can sense sounds with higher frequencies Birds, turtles, and amphibians use magnetic fields to navigate Elephants can hear very low-frequency sounds, which are used to communicate Evolution Anthony J Greene

34. Darwinian Evolution Variation • Every species has enormous diversity • Sexual reproduction insures diversity by recombining genes into new combinations • Variability allows a species (not an individual) to survive Conch Anthony J Greene

35. Darwinian Evolution Selection - reproduction of the fittest • Differential survival advantage • Differential reproduction advantage • No selection pressure after the age of reproduction Anthony J Greene Tarsier

36. Evolution of Accuracy and Acuity in Perception • Strong Selection Pressure for accurate perception. • At every stage of evolution, organisms with better perception gained a differential survival advantage • Better acuity • Larger range of detectable stimuli • Consistent representation of distal stimulus • Illusions Don't Occur in Natural Scenes -- Selection pressure for perceptual systems not to be tricked (e.g. black light) Anthony J Greene

37. We can think of variation as branching And selection as pruning There is no distinction between micro- and macro-evolution. Species alive today are the tip of the branch, not the top of a ladder. Evolutionary Tree of Life Anthony J Greene

38. Neuroscience:Review of Physiology Central Nervous System (CNS) • Consists of the brain and spinal cord • Communicates with the Periphery (anything other than the brain and spinal cord) Anthony J Greene

39. Nerves • Efferent- outflow (CNS to Periphery) • Afferent- inflow (Periphery to CNS) Neurons • Motor - Associated with muscles (efferent) • Sensory - Associated with sense receptors (afferent) • Interneuron - Rest of the CNS - Makes up pathways between motor and sensory neurons and the CNS. Most of brain. Anthony J Greene

40. Cerebral Cortex White Matter Vs. Gray Matter Fissures & Sulci 1 Central Sulcus 2 Lateral (Sylvian) Fissure 3 Longitudinal Fissure Lobes 1 Temporal Lobe - Auditory Cortex - Language Processing - Object Identification (Visual-Auditory-Tactile) 2 Occipital Lobe - Visual Cortex 3 Parietal Lobe - Somatosensory Cortex - Spatial Perception (Visual-Auditory-Tactile) 5 Frontal Lobe - Motor Cortex - Behavior Control - Planning/Strategy Anthony J Greene

41. Cerebral Cortex White Matter Vs. Gray Matter Anthony J Greene

42. Corpus Collosum A P Anthony J Greene

43. Corpus Collosum A P Anthony J Greene

44. Cerebral Cortex Central Sulcus Anthony J Greene

45. Cerebral Cortex Lateral Fissure Anthony J Greene

46. Cerebral Cortex Longitudinal Fissure Anthony J Greene

47. Cerebral Cortex Temporal Lobe Anthony J Greene

48. Cerebral Cortex Occipital Lobe Anthony J Greene

49. Cerebral Cortex Parietal Lobe Anthony J Greene

50. Cerebral Cortex Frontal Lobe Anthony J Greene