THE STUDY OF PERCEPTION
Anthony J Greene
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Chapter 1 Outline
I.
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2.
3.
II.
1.
2.
Why study perception?
Perception is reality
How we percieve.
Historical Approaches
Scientific Study of Perception:
The Scientific Revolution: Hypothesis, Data & Theory
Functionalism
The problem of Perception:
•
Psychophysics
•
Evolution
Structuralism
•
Neuroscience
Anthony J Greene
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Why Study Perception?
• What we get from perception
• Perception is our only source of
information: we have no knowledge, or
experience except through perception
• Perception allows survival
• The utility of perceptual systems informs us
about why they evolved
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The way we perceive
• Perceptual systems are incredible–Nothing
man-made is even close
• The mechanisms of perceptual systems
inform us about how they evolved
• Sensory enhancement (glasses, hearing
aids),
• Sensory substitution
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A Song of Ourselves
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•
•
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Perception is not always veridical
What we are able to perceive
We are fundamentally perceptual beings
Thought, memory and experience are
perceptual (either directly or indirectly)
• Art, Music, Food, Physical Sensations etc.
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Lemon
A man makes a picture
A moving picture.
Through the light projected
He can see himself up close.
Man captures color,
Man likes to stare,
He turns his money into light
To look for her;
She is the dreamer,
She's imagination.
--U2
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Philosophical & Historical
Approaches to Perception
Realism
Subjectivism-e.g. Democritus, Plato
Dualism-e.g. Descartes
Materialism-e.g. Bacon
Nativism-e.g. Plato
Empiricism-e.g. Socrates
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Science
Derived from the Philosophies of Empiricism
& Materialism–
Fact & Theory
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Fact & Theory
•
•
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•
•
•
•
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Facts must be observable (data)
Theory = understanding
Theory is not hypothetical
Theory is broad, fact and hypothesis are narrow
Theories must be consistent with all available (relevant)
facts
Theory guides the search for fact
Facts are only important if they inform theory
Theory is more important than fact
The progress of theory is the purpose of science
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The
Advancement
of Theory
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Scientific Approaches to
perception
Functionalism (purposes of perception)
1. Evolution
2. Psychopohysics
Structuralism (mechanisms of perception)
1. Neuroscience
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Perceptual Systems
Vision
• Object Identification/recognition
• Spatial Vision: Navigation & Motion Perception
Audition
• Object Identification/recognition
• Object Localization
Touch
• Object Identification/recognition
• Pain (detection of tissue damage)
• Proprioception
Gustation & Olefaction
• Chemical detection and identification
• Nutrition & and poison avoidance
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Problem of Perception
1
2
3
4
5
Cornea
Lens
Retina
Optic Nerve
Brain
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Proximal vs. Distal Stimulation
Proximal Stimulus is upside down
• The brain is not looking at retinal pictures
Proximal stimulus is 2 dimensional (Depth
Perception)
• 3rd dimension is lost from distal to proximal,
however we perceive in 3 dimensions
• How does then do we experience a 3rd
dimension?
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Perceptual Experience Mirrors
Distal Stimulation
1 Size Constancy
2 Shape Constancy
3 Position Constancy
4 Brightness Constancy
5 Color Constancy
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Size Constancy
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Size Constancy
If object moves 2x further away, the
retinal image decreases by a factor of 2,
but we do not perceive it to shrink
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Shape Constancy
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Position Constancy
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Brightness Constancy
A light meter would read that the right side of
the panel is
white and that the left side is gray
Visual systems interpret them both as white
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Color Constancy
• Under different ambient lighting conditions, the
mondrian will reflect different frequencies (as
measured by a light meter). e.g. green light
reflected off a red surface would be read by a light
meter as orange or yellow
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Brightness Constancy
• Visual systems compensate for ambient
lighting, so that under almost all conditions
the colors appear stable
• There are instances when there does not
exist a correspondence between distal image
and perception (illusions and ambiguity)
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• Cases where our
perceptual
experience is
inaccurate
• How does the
brain get tricked?
Illusions
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Illusions
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Perceptual Ambiguity
One proximal stimulus produces many
perceptual experiences
Perceptual experience is not just a function of
what hits the eye
The man bent over his guitar
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The Man With The Blue Guitar
A shearsman of sorts. The day was green.
They said, "You have a blue guitar,
You do not play things as they are."
The man replied, "Things as they are
Are changed upon the blue guitar."
And they said then, "But play, you must,
A tune beyond us, yet ourselves,
A tune upon the blue guitar
Of things exactly as they are."
--Wallace Stevens.
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Psychophysics
•
•
Psychophysics: The science of defining
quantitative relationships between physical and
psychological (subjective) events
Fechner (1801–1887) invented psychophysics,
thought to be the true founder of experimental
psychology
–
Pioneering work relating changes in the physical
world to changes in our psychological experiences
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Psychophysics (cont’d)
• Weber (1795–1878) discovered that the
smallest change in a stimulus, such as the
weight of an object, that can be detected is a
constant proportion of the stimulus level:
“Weber’s Law”
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Psychophysics (cont’d)
• JND (Just Noticeable Difference): The
smallest detectable difference between two
stimuli, or the minimum change in a
stimulus that can be correctly judged as
different from a reference stimulus. Also
known as difference threshold
• Two-point threshold: The minimum
distance at which two stimuli (e.g., two
simultaneous touches) can be distinguished
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Psychophysics (cont’d)
Fechner’s
Law:
Relationship
between
stimulus
magnitude and
resulting
sensation
magnitude is
exponential.
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Psychophysics (cont’d)
Stevens’ Power
Law:
Relationship
between stimulus
magnitude and
resulting
sensation
magnitude.
Exponent can be
positive, zero, or
negative.
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Evolution
Some species sense energies
that humans cannot:
– Bees see ultraviolet lights
– Rattlesnakes sense infrared
energy
– Dogs and cats can sense
sounds with higher
frequencies
– Birds, turtles, and
amphibians use magnetic
fields to navigate
– Elephants can hear very lowfrequency sounds, which are
used to communicate
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Darwinian
Evolution
Variation
• Every species has
enormous diversity
• Sexual reproduction
insures diversity by
recombining genes
into new
combinations
• Variability allows a
species (not an
individual) to
survive
Conch
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Darwinian
Evolution
Selection reproduction of the
fittest
• Differential
survival advantage
• Differential
reproduction
advantage
• No selection
pressure after the
age of reproduction
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Tarsier
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Evolution of Accuracy and
Acuity in Perception
• Strong Selection Pressure for accurate perception.
• At every stage of evolution, organisms with better
perception gained a differential survival advantage
• Better acuity
• Larger range of detectable stimuli
• Consistent representation of distal stimulus
• Illusions Don't Occur in Natural Scenes -Selection pressure for perceptual systems not to be
tricked (e.g. black light)
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Evolutionary Tree of Life
• We can think of variation as branching
• And selection as pruning
• There is no distinction between micro- and
macro-evolution.
• Species alive today are the tip of the branch,
not the top of a ladder.
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Neuroscience:
Review of Physiology
Central Nervous System
(CNS)
• Consists of the brain
and spinal cord
• Communicates with the
Periphery (anything
other than the brain and
spinal cord)
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Nerves
•Efferent- outflow (CNS to Periphery)
•Afferent- inflow (Periphery to CNS) Neurons
•Motor - Associated with muscles (efferent)
•Sensory - Associated with sense receptors
(afferent)
•Interneuron - Rest of the CNS - Makes up
pathways between motor and sensory neurons and
the CNS. Most of brain.
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Cerebral Cortex
White Matter Vs. Gray Matter
Fissures & Sulci
1 Central Sulcus
2 Lateral (Sylvian) Fissure
3 Longitudinal Fissure
Lobes
1 Temporal Lobe - Auditory Cortex - Language Processing - Object
Identification (Visual-Auditory-Tactile)
2 Occipital Lobe - Visual Cortex
3 Parietal Lobe - Somatosensory Cortex - Spatial Perception (VisualAuditory-Tactile)
5 Frontal Lobe - Motor Cortex - Behavior Control - Planning/Strategy
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Cerebral Cortex
White Matter Vs. Gray Matter
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Corpus Collosum
A
P
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Corpus Collosum
A
P
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Cerebral Cortex
Central Sulcus
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Cerebral Cortex
Lateral Fissure
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Cerebral Cortex
Longitudinal Fissure
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Cerebral Cortex
Temporal Lobe
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Cerebral Cortex
Occipital Lobe
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Cerebral Cortex
Parietal Lobe
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Cerebral Cortex
Frontal Lobe
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Neurons
The Basic Neuron
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Neurons
The Synapse
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Neurons
The Action Potential
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Perceptual Processes
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Perceptual Processes
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01 The Study of Perception