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Sensation and Perception Sensation vs. Perception • Sensation vs. Perception • Physical stimulus → Physiological response → Sensation and Perception Sensory experience & interpretation • Example vision research questions: Chapter 5 – How does the eye take light and transform it into a message the brain can understand? Vision: p. 135 - 156 – How do we see a stable world even though our eyes are constantly blinking and shifting? – How do perceptual illusions trick the mind? Visual system Physical properties of light • Wavelength – Hue • Amplitude – Intensity/brightness • Mix of wavelengths – Saturation The Eye Blindspot demonstration Transduction Process to translate light into an electro- chemical message for the brain Accommodation Lens changes shape to focus light on retina Demo in text p.141 http://faculty.washington.edu/chudler/chvision.html 1 Vision problems Photoreceptors Accomodation = shape of lens changes to focus Rods Flexibility lost with increased age = Presbyopia – Concentrated in periphery of retina – Low light ok – No detail, no color Cones – Concentrated in fovea – Needs full light – High visual acuity – Color receptors http://faculty.washington.edu/chudler/sight.html The three main layers of the retina Dark adaptation Color theories Opponent-process theory E. Herig Photopigments have to be regenerated by cells Trichromatic theory H. von Helmholz Negative afterimage Lilac Chaser • http://michaelbach.de/ot/col_lilacChaser/index.html http://faculty.washington.edu/chudler/after.html Text demo p155 http://michaelbach.de/ot/col_rapidAfterimage/index.html 2 Center-Surround Receptive Fields Luminance and contrast • 126 million receptors in retina • Convergence allows many receptors to use 1 neuron for afferent signaling • Center-Surround receptive fields allow for more than 1 signal to be sent by 1 afferent neuron • Either excitatory or inhibitory for each region http://michaelbach.de/ot/lum_herGrid/index.html Motion perception Rotating Snake • Phi phenomenon • http://michaelbach.de/ot/mot_rotsnake/ind – Max Wertheimer (1912) ex.html – Motion via still images – http://michaelbach.de/ot/mot_reverse- phi/index.html • Motion illusions – Motion aftereffect – http://michaelbach.de/ot/mot_adapt/index.html Thought paper • What perceptual work is required by a baseball player to hit a baseball? • Dynamic visual acuity: see moving object, see rotation of object Object (or Pattern) • Depth perception: see how far away it is Recognition • Tracking: keep eyes fixed on moving object • Object recognition: separate object from field How do we interpret lines and • Contrast sensitivity: see object color against patterns as objects? background color • Pick up on other cues specific to sport 3 Gestalt principles of organization Which gestalt law? • Laws of “perceptual organization”: see whole • Figure vs. ground – Proximity – Similarity – Closure – Good continuation – Common fate Gestalt principles Biological motion • Group objects together to find the 13 faces • http://michaelbach.de/ot/mot_biomot/index .html • Which gestalt law?? What are the depth cues? Depth perception • Monocular cues – Linear perspective – Acuity – Color and brightness – Shadow or occlusion – Relative height – Relative motion http://michaelbach.de/ot/mot_ske/index.html 4 Depth perception Pattern recognition • Binocular cues • Bottom-up processing – Retinal disparity – Information from sensory receptors – Convergence • Depth illusions • Top-down processing – Ames room – Information from knowledge and expectations • Perceptual constancies Feature detectors Visual disorders • Agnosia: deficit in recognizing objects • Specialized receptors in Cell’s responses – Book: “The man who mistook his wife for a hat” by Oliver Sacks visual cortex – Prosopagnosia ( deficit for faces) – Hubel & Weisel , 1962 • http://www.youtube.com/watch?v=XLGXAiSpN00 Stimulus • http://www.faceblind.org/ • Simple cells – Akinetopsia (deficit for objects in motion) – Orientation specific • Suggests regions of the cortex designed to • Complex cells processes certain parts of visual input – Movement, faces, etc. • “What” system – Damage to occipital-temporal pathway • How does brain pull • “Where” system information together? – Damage to occipital-parietal pathway Ungerleider & Mishkin (1983) Perceptual parsing • Detect and identify primary 3d objects or geons (Biederman, 1987) • Method with monkeys: – Object discrimination task – Landmark discrimination problem • IV: lesion site (temporal lobe vs. parietal lobe) • Result: – Object discrimination deficit with temporal lesion – Landmark discrimination deficit with parietal lesion 5 Biederman’s Geons Top-down processing • Intersections are important to recognition Top-down processing Tox-Doxn Pxocxssxng • To xllxstxatx, I cxn rxplxce xvexy txirx lextex of x sextexce xitx an x, anx yox stxll xan xanxge xo rxad xt – ix wixh sxme xifxicxltx • Why are you able to read the sentence above? Another example Pattern Recognition 7H15 M3554G3 53RV35 7O PR0V3 H0W • Bottom-up AND top-down 0UR M1ND5 C4N D0 4M4Z1NG 7H1NG5! • Bi-directional model 1MPR3551V3 7H1NG5! 1N 7H3 B3G1NN1NG 17 WA5 H4RD BU7 N0W, 0N 7H15 LIN3 Y0UR M1ND 1S R34D1NG 17 4U70M471C4LLY W17H 0U7 3V3N 7H1NK1NG 4B0U7 17, B3 PROUD! 0NLY C3R741N P30PL3 C4N R3AD 7H15. PL3453 F0RW4RD 1F U C4N R34D 7H15 6 Perceptual problem solving: Impossible figures Thought paper • Think of an example from your life where you use top-down and bottom-up processing. • Explain the example. • What parts of the example use top-down processing and what parts use bottom-up processing? 7 .
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