Sensation and Perception - pingpong.ki.se · 1 Sensation and Perception Psychology I...

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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


Sensory Receptors


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


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


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


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


Adelson: Machine Vision Challenges


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Adelson: Machine Vision 3


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


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

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