Sensation and Perception. Sensation. Sensory Receptors. Sensation. General Properties of Sensory Systems

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1 Sensation and Perception Psychology I Sjukgymnastprogrammet May, 2012 Joel Kaplan, Ph.D. Dept of Clinical Neuroscience Karolinska Institute joel.kaplan@ki.se General Properties of Sensory Systems Sensation: Information arriving from sense organs (eye, ear, etc.) Perception: Mental process of organizing sensations into meaningful patterns Data Reduction System: Any system that selects, analyzes, and condenses information Sensation Sensory Receptors Specialized cells that detect and transmit sensory information to the brain These cells respond selectively to stimulation Cells send signals via distinct neural pathways 2008 The McGraw-Hill Companies, Inc. Sensory Receptors Sensation Photoreception (Vision) Detection of light Mechanoreception (Touch) Detection of pressure, vibration, and movement Chemoreception (Smell and Taste) Detection of chemical stimuli 2008 The McGraw-Hill Companies, Inc The McGraw-Hill Companies, Inc. 1

2 Animation: Effect of Sound Waves on Cochlear Structures Skin: Highly Specialized Somato-Sensory Receptors Sensory Thresholds Vision A candle flame seen at 30 mi. on a clear, dark night Slide 10 Hearing Taste Smell Touch The tick of a watch under quiet conditions at 20 ft. One teaspoon of sugar in 2 gallons of water 1 drop of perfume diffused into the entire volume of a 3 room apartment The wing of a bee falling on your cheek from a height of 1 cm 2007 The McGraw-Hill Companies, Inc. All Rights Reserved Sensation 1. Stimulus is received by sensory receptors. Sensation Perception 3. Feature detectors analyze stimulus features. 5. Neural representation is compared with previously stored information in brain. Perception Bottom-up and Top-Down Processing Perception consists of the progression of recognizing and processing information from individual components of a stimuli and moving to the perception of the whole. Top-down and bottom-up processing occur simultaneously and interact with each other in our perception of the world around us. 2. Receptors translate stimulus properties into nerve impulses (transduction). 4. Stimulus features are reconstructed into neural representation. 6. Matching process results in recognition and interpretation of stimulus. BOTTOM-UP PROCESSING Combination and interpretation of whole Breakdown/analysis of stimuli TOP-DOWN PROCESSING Concept, Expectation Guides, analysis Detection of individual stimulus elements Interpretation of incoming stimuli 2

3 Churchland: Unconscious Inferences Top Down Processing [14:10-17:16] The Visual System does a lot with limited information That is a good thing because the neural processing capacity of each of the sensory systems is also limited. So perception involves numerous shortcuts and clever techniques for extracting relevant information. Sometimes such shortcuts can create misperception, as revealed by various illusions. Perceptual Organization- Gestalt Visual Capture tendency for vision to dominate the other senses Grouping the perceptual tendency to organize stimuli into coherent groups Perceptual Organization- Gestalt PerceptualOrganization- Grouping Principles Gestalt- an organized whole tendency to integrate pieces of information into meaningful wholes Grouping Principles proximity- group nearby figures together similarity- group figures that are similar continuity- perceive continuous patterns closure- fill in gaps connectedness- spots, lines and areas are seen as unit when connected 3

4 Law of Similarity Law of Closure Kanizsa square The Blind Spot Mach Bands - Edge Enhancement Illusion Fig. 5.8 Experiencing the blind spot. (a) With your right eye closed, stare at the upper right cross. Hold the book about 1 foot from your eye and slowly move it back and forth. You should be able to locate a position that causes the black spot to disappear. When it does, it has fallen on the blind spot. With a little practice you can learn to make people or objects you dislike disappear too! (b) Repeat the procedure described, but stare at the lower cross. When the white space falls on the blind spot, the black lines will appear to be continuous. This may help you understand why you do not usually experience a blind spot in your visual field. Fig. 6.1 Shape constancy. (a) When a door is open its image actually forms a trapezoid. Shape constancy is indicated by the fact that it is still perceived as a rectangle. (b) With great effort you may be able to see this design as a collection of flat shapes. However, if you maintain shape constancy the distorted squares strongly suggest the surface of a sphere. (From Spherescapes-1 by Scott Walter and Kevin McMahon, 1983.) 4

5 Perceptual Organization- Depth Perception Depth Perception ability to see objects in three dimensions allows us to judge distance Binocular cues retinal disparity images from the two eyes differ closer the object, the larger the disparity convergence neuromuscular cue two eyes move inward for near objects Monocular Cues for Depth Perception The Ponzo Illusion Monocular Cues for Depth Perception Relative Size Powerful Depth Illusion The Ames Illusion Face Recognition [28:00-32:06] 5

6 Image From Mars A Top Down Contribution to Face Recognition (Memory, Experience): [33:27-34:53] Top-down processing is also illustrated by the importance of context in determining how we perceive objects. Top Down Processing Example Who is afraid? Who may be violent? The power of context is shown in this figure. Note how the B and the 13 are identical. (Source: Coren & Ward, 1989.) Eye Movements Snapshot? Still Life If eyes don t move, the image disappears 6

7 Sensory Adaptation Eye Tracking Fig. 6.5; (a) A projector mounted on a contact lens makes the projected image move with the eye. (b) Initially, the person sees the stabilized image, but soon she sees fragments fading and reappearing. Figure-Ground Principle of Perceptual Organization Bi-stability Example: Necker Cube [43:04-45:15] Pay Attention! Attention and Concentration Can Influence What Is Seen (perceived) And What Is Not Seen 7

8 Moon-walking Bear Change Blindness Auditory Perception Many of the same principles apply to sound perception (hearing). The Ear is Not a Tape Recorder Formants: Frequency Band Decomposition of Human vowel sounds Multimodal Integration More than one sense modality Can influence perception Example The McGurk Effect Vision has strong influence on speech Perception Vision and Touch Can Influence Our Body Perception Rubber Hand Illusion 8

9 The redder the drink, the sweeter the taste. Movshon: Intro to Brain Anatomy [13:00-18:23] Growth in size and importance of the associative areas of the brain, from rats to cats to humans. Green = sensorimotor area, red = visual area, blue = auditory area. 9

10 Sensory Pathways Schematics Sensory Systems [Cartoon] Somatosensory System [Schematic] Kandel: Visual System Overview Movshon: Visual System Anatomy [4:10-8:11] [8:12-12:42] Sense of Vision From the retina to the visual cortex The optic nerves carry impulses to the optic chiasm» Fibers from the right half of each retina converge and continue through the right optic tract» Fibers from the left half of each retina converge and continue through the left optic tract Fibers from the optic tracts synapse with neurons in the thalamus Axons from the thalamus carry impulses to the primary visual areas of the occipital lobes The right and left visual cortex perform higher visual processing tasks 10

11 Receptive Field Properties Of Visual Neuons Recording Setup Processing Within Retina Ganglion Cell Output: Round Receptive Fields: Center/Surround Ganglion cells not particularly responsive to changes in illumination that include center and surround Rather, sensitive to center/surround differences Contrast is key, not absolute illumination Primary Visual Cortex: Area 17) Simple Cell Receptive Field Adelson: Machine Vision 1 Adelson: Machine Vision Challenges [12:40-14:16] [29:00-33:01] 11

12 Adelson: Machine Vision 3 Kornwisher: Face Recognition Localization of Function [41:00-43:02] [20:00-25:47] Localization of Function for Recognition of Faces, Places, etc. Kornwisher: Letter/Character Recognition Localization of Function [34:14-35:35] Localization of Function for Letter/Character Recognition Agnosias: Intro 12

13 Initial, Mostly Unconscious Activation Of Primary Sensory Cortex Information Broadcast to Many Regions Neglect, Attention, Awareness Hemi-Neglect Syndrome :40-27:48 MRI Scan In Patient with Hemi-Neglect Failure to Broadcast Global Workspace Model 13

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