THE STUDY OF PERCEPTION
Anthony J Greene 1

Chapter 1 Outline
I.
Why study perception?
1.
Perception is reality
2.
How we percieve.
3.
Historical Approaches
II.
Scientific Study of Perception:
The Scientific Revolution: Hypothesis, Data & Theory
1.
Functionalism
The problem of Perception:
• Psychophysics
•
Evolution
2.
Structuralism
•
Neuroscience
Anthony J Greene 2

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
Anthony J Greene 3

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
Anthony J Greene 4

A Song of Ourselves
• 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.
Anthony J Greene 5

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
• 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 Cornea
2 Lens
3 Retina
4 Optic Nerve
5 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: 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
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Conch
34

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 (Visual-
Auditory-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
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Corpus Collosum
A
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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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Parietal Lobe
Cerebral Cortex
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Frontal Lobe
Cerebral Cortex
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The Basic Neuron
Neurons
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The Synapse
Neurons
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The Action Potential
Neurons
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Perceptual Processes
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Perceptual Processes
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