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Sensation and Perception
Psychology ISjukgymnastprogrammet
May, 2012
Joel Kaplan, Ph.D.Dept of Clinical Neuroscience
Karolinska [email protected]
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
© 2008 The McGraw-Hill Companies, Inc.
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
© 2008 The McGraw-Hill Companies, Inc.
Sensation
Photoreception (Vision) Detection of light
Mechanoreception (Touch) Detection of pressure, vibration, and movement
Chemoreception (Smell and Taste) Detection of chemical stimuli
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Animation: Effect of Sound Waves on Cochlear Structures
Skin: Highly Specialized Somato-Sensory Receptors
© 2007 The McGraw-Hill Companies, Inc. All Rights Reserved
Slide 10Sensory Thresholds
VisionA candle flame seen at 30 mi. on a clear, dark night
Hearing The tick of a watch under quiet conditions at 20 ft.
TasteOne teaspoon of sugar in 2 gallons of water
Smell1 drop of perfume diffused into the entire volume of a 3 room apartment
TouchThe wing of a bee falling on your cheek from a height of 1 cm
Sensation Perception
PerceptionSensation
2. Receptors translate stimulus properties into nerve impulses (transduction).
3. Feature detectors analyze stimulus features.
4. Stimulus features are reconstructed into neural representation.
1. Stimulus isreceived bysensory receptors.
5. Neural representationis compared with previously stored information in brain.
6. Matching process results in recognition and interpretation of stimulus.
“Bottom-up” and “Top-Down” ProcessingPerception 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.
Concept, Expectation
Guides, analysis
Interpretation of incoming stimuli
Combination and interpretation of “whole”
Breakdown/analysis of stimuli
Detection of individual stimulus elements
BOTTOM-UP PROCESSING TOP-DOWN PROCESSING
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Churchland: Unconscious Inferences – Top Down Processing
http://www.charlierose.com/view/interview/12025 [14:10 -17:16] http://www.biomotionlab.ca/Demos/BMLwalker.html
The Visual System does a lot with limited information
That is a good thing because the neural processingcapacity of each of the sensory systems is also limited.
So perception involves numerous shortcuts and clevertechniques for extracting relevant information.
Sometimes such shortcuts can create ‘misperception,’as revealed by various illusions.
Perceptual Organization-Gestalt
Visual Capturetendency for vision to dominate the
other senses
Groupingthe perceptual tendency to organize
stimuli into coherent groups
Perceptual Organization-Gestalt
Gestalt- an organized wholetendency to integrate pieces of information
into meaningful wholes
Grouping Principlesproximity- group nearby figures togethersimilarity- group figures that are similarcontinuity- perceive continuous patternsclosure- fill in gapsconnectedness- spots, lines and areas are
seen as unit when connected
PerceptualOrganization-Grouping Principles
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Law of Closure
Law of Similarity
Kanizsa square
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.
The Blind SpotMach Bands - Edge Enhancement Illusion
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.)
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Perceptual Organization-Depth Perception
Depth Perceptionability to see objects in three dimensionsallows us to judge distance
Binocular cuesretinal disparityimages from the two eyes differ closer the object, the larger the disparity
convergenceneuromuscular cuetwo 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
http://www.charlierose.com/view/interview/12099 [28:00-32:06]
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Image From Mars
A Top Down” Contribution to Face Recognition(Memory, Experience):
http://www.charlierose.com/view/interview/12099 [33:27 - 34:53]
The power of context is shown in this figure. Note how the B and the 13 are identical.
(Source: Coren & Ward, 1989.)
•Top-down processing is also illustrated by the importance of context in determining how we perceive objects.
Top Down Processing ExampleWho is afraid? Who may be violent?
Eye MovementsSnapshot? Still Life
If eyes don’t move, the image disappears
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Sensory Adaptation
Fig. 6.5; (a) A projector mounted on a contact lens makes theprojected image move with the eye. (b) Initially, the person seesthe stabilized image, but soon she sees fragments fading and reappearing. http://www.youtube.com/watch?v=e5Sa3H8QN6c
Eye Tracking
“Figure-Ground” Principle of Perceptual Organization
Bi-stability Example: Necker Cube
http://www.charlierose.com/view/interview/10727 [43:04 - 45:15]
Attention and Concentration CanInfluence What Is Seen (perceived)
And What Is Not Seen
http://www.youtube.com/watch?v=0grANlx7y2E
Pay Attention!
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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 IntegrationMore than one sense modality
Can influence perception
Example “The McGurk Effect”
Vision has strong influence on speech Perception
http://www.youtube.com/watch?v=G-lN8vWm3m0
Vision and Touch Can Influence Our Body Perception
“Rubber Hand Illusion”
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http://www.youtube.com/watch?v=sxwn1w7MJvk&feature=relmfu
The redder the drink, the sweeter the taste.
Movshon: Intro to Brain Anatomy
http://www.charlierose.com/view/interview/10694 [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.
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Sensory Pathways Schematics
Sensory Systems[Cartoon]
Somatosensory System[Schematic]
Kandel: Visual System Overview
http://www.charlierose.com/view/interview/10727 [4:10 -8:11]
Movshon: Visual System Anatomy
http://www.charlierose.com/view/interview/10727 [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
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Receptive Field PropertiesOf 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
http://www.charlierose.com/view/interview/10727 [12:40-14:16]
Adelson: Machine Vision Challenges
http://www.charlierose.com/view/interview/10727 [29:00-33:01]
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Adelson: Machine Vision 3
http://www.charlierose.com/view/interview/10727 [41:00-43:02]
Kornwisher: Face Recognition Localization of Function
http://www.charlierose.com/view/interview/10727 [20:00 -25:47]
Localization of Function forRecognition of Faces, Places, etc.
Kornwisher: Letter/Character RecognitionLocalization of Function
http://www.charlierose.com/view/interview/10727 [34:14 - 35:35]
Localization of Function forLetter/Character Recognition
Agnosias: Intro
http://www.charlierose.com/view/interview/12099 - 2:54-6:28
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Initial, Mostly Unconscious ActivationOf Primary Sensory Cortex
Information “Broadcast” toMany Regions
Neglect, Attention, Awareness
http://www.charlierose.com/view/interview/12099 --17:40-27:48
Hemi-Neglect Syndrome
MRI ScanIn Patient with Hemi-Neglect
“Failure to Broadcast”Global Workspace Model