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Anthony J Greene 1

THE STUDY OF PERCEPTION

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Anthony J Greene 2

Chapter 1 Outline

I. Why study perception?

1. Perception is reality2. 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

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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 incredibleNothing

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

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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LemonA man makes a pictureA 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 PerceptionRealism

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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TheAdvancement

of Theory

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Scientific Approaches to

perceptionFunctionalism (purposes of perception)

1. Evolution

2. Psychopohysics

Structuralism (mechanisms of perception)

1. Neuroscience

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Perceptual SystemsVision

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 (DepthPerception)

3rd dimension is lost from distal to proximal,however we perceive in 3 dimensions

How does then do we experience a 3rddimension?

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Perceptual Experience Mirrors

Distal Stimulation1 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 lightreflected 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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Illusions Cases where our

perceptual

experience is

inaccurate

How does the

brain get tricked?

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Illusions

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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

Perceptual Ambiguity

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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 (18011887) invented psychophysics,

thought to be the true founder of experimental

psychology

Pioneering work relating changes in the physicalworld to changes in our psychological experiences

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Psychophysics (contd)

Weber (17951878) discovered that the

smallest change in a stimulus, such as the

weight of an object, that can be detected is aconstant proportion of the stimulus level:

Webers Law

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Psychophysics (contd)

JND(Just Noticeable Difference): Thesmallest detectable difference between two

stimuli, or the minimum change in a

stimulus that can be correctly judged asdifferent from a reference stimulus. Also

known as difference threshold

Two-point threshold:The minimumdistance at which two stimuli (e.g., two

simultaneous touches) can be distinguished

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Psychophysics (contd)

Fechners

Law:Relationship

between

stimulusmagnitude and

resulting

sensationmagnitude is

exponential.

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StevensPower

Law:Relationship

between stimulus

magnitude andresulting

sensation

magnitude.

Exponent can be

positive, zero, or

negative.

Psychophysics (contd)

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EvolutionSome species sense energies

that humans cannot: Bees see ultraviolet lights

Rattlesnakes sense infrared

energy

Dogs and cats can sensesounds with higher

frequencies

Birds, turtles, and

amphibians use magneticfields to navigate

Elephants can hear very low-

frequency sounds, which are

used to communicate

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Darwinian

EvolutionVariation Every species has

enormous diversity

Sexual reproductioninsures diversity byrecombining genesinto new

combinations Variability allows a

species (not anindividual) to

survive

Conch

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Darwinian

EvolutionSelection -reproduction of thefittest

Differentialsurvival advantage

Differentialreproduction

advantage No selection

pressure after theage of reproduction

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- andmacro-evolution.

Species alive today are the tip of the branch,not the top of a ladder.

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Neuroscience:

Review of PhysiologyCentral Nervous System

(CNS)

Consists of the brainand spinal cord

Communicates with thePeriphery (anythingother than the brain andspinal 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 andthe CNS. Most of brain.

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Cerebral CortexWhite Matter Vs. Gray MatterFissures & Sulci

1 Central Sulcus

2 Lateral (Sylvian) Fissure

3 Longitudinal FissureLobes

1 Temporal Lobe - Auditory Cortex - Language Processing - ObjectIdentification (Visual-Auditory-Tactile)

2 Occipital Lobe - Visual Cortex3 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 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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NeuronsThe Action Potential

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Perceptual Processes

Perceptual Processes

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Perceptual Processes