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The Process of Perception: Martians on Earth?

Explore the fascinating process of perception, from the workings of sensory receptors to the transformative power of neural processing. Discover the role of knowledge and awareness in shaping our perceptual experience.

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The Process of Perception: Martians on Earth?

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  1. Psy 280: Perception Prof. Anderson Department of Psychology Week 2

  2. Part 1: The process of perception

  3. Martians on earth? • 2 front facing spherical sensors • Light reactive chemical • 2 fleshy antennae on side of head • Pressure sensitive hairs • Cutaneous membrane • Little detectors of different shapes • Temperature, pain, caress • Bilateral air holes • Chemical sampling of gases • Retractable probe • Chemical sampling of solids, liquids

  4. Perception is easy • Misleading • World is projected on retina —> “vision” • Discovery of depth in art, but not perception of depth • Computer vision • MIT student summer project

  5. No privileged access to how perception works • Perception is not just about introspection • Can’t introspect about working of the brain directly • Have access to the results of complex processes

  6. What’s perception for? • Evolutionary adaptionist view • Shaped by environment to optimize fitness • Animal perception • Olfactory sensitivity in dogs • “smell face” • Bat “vision” • Bird brains: Magnetic fields • What do they help us do? • Perceptual toolbox • Work with environment • What is perception for? • What's the problem to be solved? • What sense would you choose to lose?

  7. Sensation vs. Perception • Sensation: workings of peripheral sensory receptors • Receptors are like little specialized “peripherals” • Retina: Does your retina see? • What’s frog vision like? • Hardwired? • Perception: working of the brain • The big CPU • Influence of knowledge, learning • Consciousness • Sensation & Perception • It’s not a clear distinction

  8. The process of perceiving • The big question: Where/when does “perception” start? • Start with the stimulus? • Not exactly • A tree falls in the forest … • Don’t see things behind your head? • Must being looking at stimulus • “Attention”

  9. Receptors • Stimulus must fall on receptors • More restrictive for vision than hearing (< 180°) • What would vision be like if 360°? • E. Abott’s “flatlands” • Don’t “perceive” what’s on receptors • E.g., inverted retinal image • Don’t see world upside down • Poke yourself in the eye! • What’s up is down • What’s right is left • No need to “flip” image • Or twist optic nerve

  10. The magic of sensory transduction • Transference of energy from one form to another • Physical/environmental energy to biological energy • Photosynthesis: Chemical energy • Plants, bacteria • Sunlight—> sugar—>ATP (fuel) • Sensory transduction: Electrical energy • Retina: Light—>chemical—>electrical • Sensation: Process of transduction for different sensory systems • E.g., Touch: physical compression —> electrical energy

  11. Neural processing I • Where does it start? • Receptors—>Brain/neurons • Definition of periphery vs. brain • Brain is where signal becomes electrical • Retinal photoreceptors are not part of the brain

  12. Neural processing II • If you think the retina is complicated … • Hundreds of thousands of receptors in retina • Billions of neurons • Complexity comes from the connections • Each neurons has ~ 1000 connections • Not random connections • Controls flow of information

  13. Neural processing III • What's the processing part? • Transformations and products • Malt—>Beer • light—>sight of beer

  14. Perception I • Transformation of electrical information into perceptual experience • Depends on critical brain stages after receptor transduction • Perception is conscious sensory experience? • Depends who you ask: Different research traditions • Can you have perception without awareness? • Subception (1940-50s) • processing of emotionally significant information unconsciously

  15. Perception II: Bottom-up vs. Top-Down • Prof Anderson says: “This is where the cool stuff happens” • Can perception take place without knowledge of the world? • Bottom-up • Information coming from receptors on up • Top down • Brain is not “Tabula rasa” • What effect does knowledge play in guiding the perceptual process • Knowledge is “higher-order”, receptors “lower-order” • Computer vision • Goal: perception based entirely on bottom up analysis

  16. Knowledge dependence of perceptual processing • Is knowledge needed to derive cup shape? • Or can object be “drawn” in minds eye without knowledge? • E.g. Gestalt grouping • Good continuation • Computers find task very difficult

  17. Perception is much more than the stimulus • It’s a constructive creative process T E PE TE MY T PE

  18. Recognition I • Perception’s contact with meaning • Can we dissociate perception and recognition? • Yes and no • Brain damage: Visual agnosia • Vision w/out knowledge

  19. Can you perceive without accessing knowledge? • Modularity • Certain bottom-up perceptual processes are not influenced by knowledge • Cognitive impenetrability • Visual illusions still occur despite knowing they are illusions

  20. A mind is a terrible thing to waste (and taste) • Its almost impossible to not use your knowledge • Can’t ask you to not recognize a word • Just process color, orientation of lines • Knowledge irrevocably changes the process of perception T E PE TE MY T PE

  21. Where do top down influences on perception start? • Does knowledge (cognition), desire (emotion) influence how your retina works? • If you’re hungry does your retina start looking for steak? If you mentally imagine a steak does it appear on your retina? • Unlikely. Rather, occurs at some later (higher) stage in your brain

  22. Recognition II • Can we have recognition without perception? • Access knowledge without perceptual awareness? • Yes • e.g., Amygdala unconscious recognition of aversive stimuli (associated with shock) • Unconscious semantic priming

  23. Part 2: From brain to perception and back again • Levels of analysis • Study experience (psychology) • Study brain (neuroscience) • Study relation between mind and brain • Psychophysical analysis (Fechner, 1860s) • Phenomenology (quality of experience, W. Wundt) • Wundt focused on qualitative studies • Quantify relation between “objective” stimulus energy (physics) and “subjective” experience (psycho) • Physiological analysis (nonhuman animals) • How does electrical activity in brain relate to presented stimuli • Difficult to assess experience

  24. Human functional neuroimaging • Can assess the relation between stimulus, neural response, and experience conjointly

  25. What's the relation between mind and brain • Brain ultimately determines perception • Can look to the brain for physiological characteristics to tell us how perception works • Can also look to perception for how brain is organized • E.g., weird illusions

  26. Silly human tricks: Psychophysical methods I • Relation between stimulus and resulting perception • The Phenomenological method • Typically illusions • Detection • Its all about thresholds • Visual, auditory, touch, etc • Types of methods • Limits (up/down staircases) • Adjustment (volume knob) • Constant stimuli (find amount of energy where 50% correct detection) Arcane fact # 1

  27. Silly human tricks: Psychophysical methods II • Difference thresholds (Weber) • Smallest detectable difference between two stimuli • The Weber fraction • Amount of weight increases but proportion stays constant • = Difference/standard • This applies to most senses • Think of it like the discovery of the gravitational constant but applied to mental activity 5/100=.05 10/200=.05

  28. Signal Detection Theory 100 • Problems with sensory thresholds • “I hear/see it” 50% of the time • Represents true sensory threshold? • Classical psychophysical methods • No stimulus no response (wrong) • Sensory system vs observer • Liberal vs conservative criteria Liberal Conserv Percent “yes” response 0 Low High Tone Intensity

  29. Signal detection experiment • Trials with and without a stimulus (e.g., Tone) • How often respond to stimulus? Hits (H) • How often respond to no stimulus? False alarms (FA) • Vito is liberal • 90% H, 40% FA, 90 - 40 = 50% • Mario is conservative • 60% H, 10% FA, 60 - 10 = 50% • Equal discrimination

  30. Receiver operating characteritics (ROC) • Plot H vs FA • Sensitivity increases with deviation from diagonal • Observers falling on curve have equal threshold/sensitivity Liberal Cons

  31. Beyond thresholds • Magnitude estimation • “I love you this much” • I love my mom 2.46 times as much as chocolate • Give standard (say 10) • Judge other stimuli relative to standard • Stevens’s power law • Compression vs. expansion • Power functions • Perceived magnitude=constant x stimulus intensityn

  32. Part 3: Neurons and perception

  33. The Neuron Doctrine • Brain • Unicellular (common cytoplasm) vs. Multicellular • Neuron as basis for mind • Neurons are special • in brain, not other organs • Have special qualities that allow for perception • Your liver or kidneys do not have the capacity for perception • Aristotle: Heart was the origin of mind and soul

  34. Neurons and perception • Cutaneous receptor neuron • Collection of sensory axons: Nerve bundle • Axons from the the periphery (receptors) are called nerves Dendrites

  35. Basic properties of neurons • What are the fundamental units of the neural code? • Action potentials (AP) • What’s the neural code? • How do neurons represent stimulus intensity? • Neurons “fire” more APs • Do not fire larger APs • Analog to digital • Excitation: Increases # of APs • Inhibition: Decreases # of APs

  36. Localization of brain function • Perception is not created by a single neuron • It’s a result of many neurons • Antilocalizationists (Holists) • One brain system • One faculty (sensation, memory, emotion) • Localizationists • Multiple brain systems • Multiple faculties • Sensation, memory, emotion separate

  37. Phrenology • Franz Gall (Early 1800s) • Like palm reading • ~35 specific functions • 1 vs many faculties • Muscle metaphor • Bump on skull • Right and wrong • Localization of function

  38. Localization of perception:Law of specific nerve energies • Mueller (early 1800s) • Specific perceptual quality (hearing, touch, sight, taste, smell) depends on stimulation of specific nerves (“nerve energies”) • Critically depends on where in brain nerves connect to

  39. grid work of electrodes laid over the surface for stimulation and recording exposed cortex of epilepsy patient Intracranial stimulation: Perception • Epilepsy patients • Can activate sensations of smell, sight, touch, hearing, by stimulating the brain regions directly • Perception happens in brain, not receptors

  40. Specific perceptual qualities reside in distinct brain regions • The primary cortical sensory regions Taste

  41. End of Section

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