The Process of Perception: Martians on Earth?

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