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OBJECTIVES:

EXPLAIN THE DIFFERENCE BETWEEN
SENSATION AND PERCEPTION

COMPARE AND CONTRAST THE JND AND
WEBER’S LAW; AND THE ABSOLUTE
THRESHOLD AND THE SIGNAL DETECTION
THEORY

IDENTIFY AND EXPLAIN THE PARTS OF THE EYE
AND THEIR FUNCTION
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Sensation and Perception: The
Distinction
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Sensation : stimulation of sense organs
Perception: selection, organization, and
interpretation of sensory input
Sensation begins with a detectable stimulus
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Psychophysics: Basic Concepts
Transduction – the conversion of external
physical stimuli to neural impulses the brain
can understand. - KNOW WHERE AND
HOW THIS HAPPENS FOR VISION,
AUDITION, AND SMELL
 Absolute threshold: detected 50% of the
time. - ex. automatic lights turn on when a
threshold is reached.
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Concepts - continued
Just noticeable difference (JND): smallest
difference detectable - ex. 5 lb dumbell and 5.1 lb
dumbell
Weber’s law: size of JND proportional to size of
initial stimulus so you can use a ratio or percentage ex. 100 lb dumbell and 102 lb dumbell
light intensity- 8%
weight- 2%
tone frequency- 0.3%
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Psychophysics: Concepts and
Issues
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Signal-Detection Theory: predicts how and when
we detect the presence of a faint stimulus (signal)
amid background stimulation (noise)
detection depends partly on person’s experience,
expectations, motivation, level of fatigue
– Ex. Hearing the doorbell ring at a loud, crowded party
because you were expecting it to ring at a certain time
AND NO ONE ELSE HEARS IT

Sensory Adaptation: Decline in sensitivity to a
stimulus after a few minutes
– TAKE 30 SEC TO LIST AS MANY EXAMPLES OF
SENSORY ADAPTATION AS YOU CAN.
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REVIEW:

What is the difference between the JND and
Weber’s law?
– JND is the smallest difference detectable between
to similar stimuli. Weber’s law is the constant
proportion of the JND to the initial stimulus.

What is the difference between the absolute
threshold and the signal-detection theory?
– Absolute threshold is minimum amount of stimulus
detected 50% of the time. Signal-detection theory
accounts for experience, expectations, motivation,
level of fatigue, etc.
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Vision: The Stimulus

Light = electromagnetic radiation
– Amplitude (height): perception of brightness
– Wavelength: perception of color
– purity: mixing of wavelengths (colors)
• perception of saturation, or richness of colors.
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The Eye: Converting Light into Neural
Impulses
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The eye: housing and channeling
Components:
– Cornea: where light enters the eye
– Lens: focuses the light rays on the retina
• Accommodation -
– Iris: colored ring of muscle, constricts or dilates via
amount of light
– Pupil: regulates amount of light
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The Retina: An Extension of the CNS

Retina: absorbs light, processes images, and sends
information to the brain
– Fovea - clearest vision due to highest concentration of
cones

Activity - xyz
 Optic disk (Blind Spot): where the optic nerve
leaves the eye so there are no photoreceptors
 Activity – color vision
 Photoreceptor cells:
– Rods: black and white/ low light vision
– Cones: color and daylight vision
• Adaptation: becoming more or less sensitive to light as
needed
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Figure 4.7 The human eye
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Figure 4.7 The human eye
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The Retina and the Brain: Visual
Information Processing
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Light -> cornea -> lens -> iris -> pupil -> retina ->
rods and cones -> neural signals -> bipolar cells ->
optic nerve (blind spot) -> optic chiasm -> opposite
half brain ->
 HOMEWORK – COME UP WITH A MNEMONIC
DEVICE FOR REMEMBERING THE ORDER AND
PARTS OF VISION. DUE TOMORROW
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Review:

List 3 terms or concepts that you
learned today.
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Figure 4.19 Additive versus subtractive color mixing
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Visual Information
Processing

Trichromatic (three color) Theory
 Young and Helmholtz
 three different retinal color receptors
 red
 green
 blue
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Theories of Color Vision
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Trichromatic theory - Young and Helmholtz
– Receptors for red, green, blue – color mixing – F 4.21
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Opponent-Process theory – Hering
– 3 pairs of antagonistic colors – negative afterimages
– red/green, blue/yellow, black/white
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Current perspective: both theories necessary
Trichromatic theory is explained by color blindness
Opponent-Process theory is explained by the
afterimage effect
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Perception: Perceiving Forms, Patterns, and
Objects
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Reversible figures –
Perceptual sets – readiness to perceive a stimulus
in a particular way – ambiguous stimuli – effects of
motivational factors
Inattentional blindness/change blindness –
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http://www.youtube.com/watch?v=nkn3wRyb9Bk&feature=related
 http://www.youtube.com/watch?v=38XO7ac9eSs
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Feature detection theory - bottom-up processing.
Form perception - top-down processing
Subjective contours
Gestalt psychologists: the whole is more than the
sum of its parts
– Reversible figures and perceptual sets demonstrate that the
same visual stimulus can result in very different perceptions
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Principles of Perception

Gestalt principles of form perception:
– figure-ground, proximity, similarity, continuity, closure, and
simplicity
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Recent research:
– Distal (stimuli outside the body) vs. proximal (stimulus
energies impinging on sensory receptors) stimuli.
– Perceptual hypotheses
• Context
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Depth and Distance Perception
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Binocular cues – clues from both eyes together
– retinal disparity
– convergence
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Monocular cues – clues from a single eye
– motion parallax
– accommodation
– pictorial depth cues
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Stability in the Perceptual World:
Perceptual Constancies
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Perceptual constancies – stable perceptions amid
changing stimuli
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Size
Shape
Brightness
Hue
Location in space
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Emphasis on linear
perspective during the
Western Renaissance
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Optical Illusions: The Power of
Misleading Cues
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Optical Illusions - discrepancy between visual
appearance and physical reality
Famous optical illusions: Muller-Lyer Illusion,
Ponzo Illusion, Poggendorf Illusion, Upside-Down
T Illusion, Zollner Illusion, the Ames Room, and
Impossible Figures
Cultural differences: Perceptual hypotheses at work
http://www.michaelbach.de/ot/ - website with visual
illusions and other visual effects
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Hearing: The Auditory System
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Stimulus = sound waves (vibrations of molecules
traveling in air)
– Amplitude (loudness)
– Wavelength (pitch)
– Purity (timbre)
• ex. - a violin and a piano playing the same note
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Wavelength described in terms of frequency:
measured in cycles per second (Hz)
– Frequency increase = pitch increase
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The Ear: Three Divisions
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External ear (pinna): collects sound.
Middle ear: the ossicles (hammer, anvil, stirrup)
Inner ear: the cochlea
– a fluid-filled, coiled tunnel
– contains the hair cells, the auditory receptors
– lined up on the basilar membrane
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Figure 4.49 The human ear
Figure 4.50 The basilar membrane
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The Auditory Pathway
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Sound waves vibrate bones of the middle ear
Stirrup hits against the oval window of cochlea
Sets the fluid inside in motion
Hair cells are stimulated with the movement of the
basilar membrane
Physical stimulation converted into neural impulses
– TRANSDUCTION

Sent through the thalamus to the auditory cortex
(temporal lobes)
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Theories of Hearing: Place or
Frequency?
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Hermann von Helmholtz (1863)
– Place theory
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Other researchers (Rutherford, 1886)
– Frequency theory
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Georg von Bekesy (1947)
– Traveling wave theory - the whole basilar membrane does
move, but the waves peak at particular places, depending on
frequency.
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Auditory Localization: Where Did that
Sound Come From?
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Two cues critical:
Intensity (loudness)
Timing of sounds arriving at each ear
– Head as “shadow” or partial sound barrier
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Timing differences as small as 1/100,000 of a second
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The Chemical Senses: Taste
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Taste (gustation)
Physical stimulus: soluble chemical substances
– Receptor cells found in taste buds
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Pathway: taste buds -> neural impulse -> thalamus
-> cortex
– Four primary tastes: sweet, sour, bitter, and salty
– Taste: learned and social processes
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The Chemical Senses: Smell
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Smell (Olfaction)
Physical stimuli: substances carried in the air
– dissolved in fluid, the mucus in the nose
– Olfactory receptors = olfactory cilia
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Pathway: Odor molecule, Nasal Passage, Nasal
Cavity, Olfactory cilia (transduction)-> neural
impulse ->olfactory nerve (axons pass through
ethmoid bone)-> olfactory bulb (brain)->olfactory
tract (inside bulb)->olfactory cortex in temporal
lobe->limbic system
– Does not go through thalamus
– Retro-nasal Olfaction -> food in your mouth goes through
the back of your mouth to your nasal cavity where
you
Table
of smell
Contents
it.
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Figure 4.54 The olfactory system
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Skin Senses: Touch
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Physical stimuli = mechanical, thermal, and chemical energy
impinging on the skin.
Pathway: Sensory receptors -> the spinal column ->
brainstem -> cross to opposite side of brain -> thalamus ->
somatosensory (parietal lobe)
Temperature: free nerve endings in the skin
Pain receptors: also free nerve endings
– Two pain pathways: fast vs. slow
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Other Senses: Kinesthetic and
Vestibular
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Kinesthesis - knowing the position of the various
parts of the body
– Receptors in joints/muscles
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Vestibular - equilibrium/balance
– Semicircular canals
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Synesthesia – “The man who tasted shapes”
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