The Stroop Effect (1)
Red
Blue
Green
Black
Green
Blue
The Stroop Effect (2)
Green
Red
Blue
Black
Blue
Red
Definitions
• Sensation:
The process of stimulating receptors
• Perception:
Interpretation & selection of sensory input
The Retina
Made of about 107 million
transducers:
100 million rods
7 million cones
Rods
•
•
•
•
•
Mostly in the periphery
More light sensitive
Detect light and dark
Insensitive to red
Take 20-30 minutes to fully adapt to
darkness
Cones
•
•
•
•
•
Mostly in the fovea
Less light sensitive
Detect colors
Have best detail vision
Adapt fully to darkness in 2-3 minutes
The Young-Helmholtz
trichromatic theory:
The Opponent Process
Theory
Cells are connected so as to place
sensations of:
• red in opposition to green
• blue in opposition to yellow
• black in opposition to white
Color Vision
• The trichromatic theory explains
perception at the receptor level
• The opponent process theory
explains it at higher brain levels
Seeing Afterimages
In the following slide, fix your eyes
on the dot in the center of the flag
Lateral Inhibition
• Cells in the retina are connected
laterally by amacrine cells
• Works to enhance contrasts
Lateral Inhibition
See the glowing white spots where the black lines cross?
Ear Structures
Ear Structures
• Pinna: The external ear. Amplifies sound.
Funnels energy to the middle ear.
• Typanic Membrane (eardrum): Moves in
response to sound waves. Converts sound
energy to mechanical energy .
• Ossicles: The hammer (maleus), anvil
(incus), & stirrup (stapes). Transmit &
amplify motion of eardrum
Ear Structures
• Cochlea: A fluid-filled chamber. Hair cells
are attached to the basilar membrane .
Converts mechanical energy to neural
impulses.
• Bone Conduction: Sound is also
transmitted to the cochlea through contact
with skull bones. This is why your voice
sounds odd in recordings
Hearing
Sound Attributes
• Pitch: determined by frequency
• Loudness: determined by amplitude
• Timbre: Complexity of the sound (number
of component waves involved in it)
Sound Waves
Hearing Loss
Hair cells, once lost, do not regenerate
Even some children's toys can cause permanent hearing loss
Hearing Loss
Usually caused by continuous exposure to excessive noise
The louder the noise, the less exposure needed
Chemical Senses
• Consist of smell & taste
• Evoke memories, emotions
• Humans vary greatly in chemical
sensitivity
Olfaction (Smell)
• Senses vaporized
molecules
• Consists of 10
million rods
embedded in the
olfactory epithelium
Olfaction (Smell)
• Olfactory Bulbs: Matchstick-sized; Integrate
signals from the olfactory rods, send them on to
the brain
• Turbinate Bones: Filter out dust and warm
incoming air. Protect the olfactory epithelium.
• Olfactory Rods: There are more than 100
different types. Each responds to different
chemicals
Smell Sensitivity
• Sense of smell varies among animals
• Dogs have 200 million olfactory rods,
spread out in a much bigger nose
• Humans differ greatly in ability to detect
smells
• The most sensitive people are 20 times
more sensitive than the least
Taste Buds
The least numerous sensory receptors
(humans have only about 10,000)
Taste
• Involves only 4 sensations: Sweet, sour,
salty, bitter
• Most of what we consider taste is actually
smell
• Texture is very important in enjoyment of
food
• People love fats for the smooth feeling they
give food (most are tasteless)
Taste Changes
• There are no taste buds in the center of the
tongue
• Taste buds constantly replaced (like
olfactory rods)
• Taste sensitivity changes very little with age
• Enjoyment of food among the aged is
reduced by loss of sense of smell
Somasthetic Senses
•
•
•
•
Kinesthetic sense: A moving sense
Vestibular sense: Being oriented
Touch: Feeling well
Temperature
Skin Senses
• The largest sensory apparatus, involves
heat, cold, pressure, pain
• Sensitivity varies throughout the body,
reflected in the amount of brain devoted to
each section of skin
• The hands & face predominate
Pain
• Important for survival
• Motivates us to protect the body, tend injuries,
rest, seek medical help.
• Gate Theory:
– Suggests an area in the spinal cord where fastconducting nerve fibers can block the messages of
small, slow conducting fibers.
– Suggests humans can block pain even when severely
injured
– Explains why the badly injured may not even notice an
injury
Endorphins
• Slow firing of pain neurons
• Accupuncture & placebos work
through endorphin release
• "Runner's high" involves endorphin
production
• Can be blocked by endorphin-blocking
drugs
Body Senses
• Kinesthetic Sense
– Knowledge of the position and motion of body parts.
– Driven by receptors in muscles, joints, and ligaments
• Vestibular Sense
– Involves the semicircular canals & the vestibular sacs
– Senses acceleration, not uniform motion
– Motion sickness arises when vision and the vestibular
sense give rise to different messages
Subliminal Persuasion
• Influence by messages that are below
your level of awareness
Ex: taped messages that are below
auditory level
• Double-blind studies have found little
support for the efficacy of subliminal
persuasion tapes (See the following
example.)
Subliminal Persuasion
• Example:
In one study, subjects were given audio
tapes labeled for weight loss.
• Half were given actual weight loss tapes
• Half were given smoke-ending tapes
• Results:
The tapes with subliminal anti-smoking messages were
just as effective as those with weight-loss messages.
The label mattered, not the messages.
Extra-Sensory Perception
• Telepathy: Detecting others' thoughts
• Clairvoyance: Knowing things that can't be
sensed
• Precognition: Predicting the future
– Psychology is concerned with evidence
– Evidence of psychic ability under controlled conditions
is lacking
Consider this: If you could read minds, couldn't you
find something more worthy (and profitable) for your
talent than to do cheap parlor tricks?
Definitions-Psychophysics
• Absolute Threshold:
The point where you can tell the stimulus is
there vs. not there 50% of the time
• Difference Threshold:
The smallest change in the stimulus that is just
detectable 50% of the time
Psychophysics:
A World of Experience
• Detecting signals
– Signal detection theory
– Sensitivity
– Bias
Intermediate Vision
• Perceptual organization
– Figure
– Ground
Figure-Ground
We organize the
world so some
parts of a
stimulus appear
to stand out
(figure) in front
of other parts
(ground)
Gestalt Principles
• The whole is greater than the sum of
its parts.
• A group of sensory elements forms
something new that is greater than
itself
Figure-Ground
Similarity
Proximity
Good Continuation
Closure
Simplicity
Similarity
• We group things that are similar in
color, shape, etc. into single units
and see them as belonging
together
• Note in the following example how
similarity alters our perception of
the stimulus as rows vs. columns
of circles
Similarity
Repeat
Proximity
• We perceive as a unit things that
are closer together relative to
other things
• Note the tendency to see the next
example as a set of columns first,
then a set of rows, despite the fact
the horizontal distance between
circles doesn't change
Proximity
Repeat
Good Continuation
• We group things together if they
appear to form a continuous pattern
Example: lines are continued through if they
cross other lines
• In the next example, we see the
stimulus as a wavy line crossing a
straight line, although numerous other
interpretations are possible.
Good Continuation
Repeat
Closure
We tend to complete figures with
gaps in them, by ignoring the gaps
and mentally filling in what we
believe should be there
Good Continuation
Repeat
Simplicity
• We tend to impose the simplest,
best-fitting interpretation on any
stimulus.
• In the following picture, we tend to
see overlapping simple geometric
figures rather than complex
Good Continuation
Repeat
Depth Perception
• Cues can be monocular or
binocular
• Some appear to be innate,
whereas others appear to be
learned
Binocular Cues
Convergence -- the lenses of your
eyes move closer together when
things are close, farther apart
when things are farther away
Convergence
Repeat
Binocular Cues
Binocular Disparity -• Each eye gets a different picture of the
world
• The greater the difference between
the pictures, the closer the object
Monocular Cues
• Linear Perspective -parallel lines converge into the distance
• Relative Size -bigger things appear to be closer
• Texture Gradient -textures become finer as things become
more distant.
Monocular Cues
• Shading -Shadowing distinguishes bulges from
indentations
Largely a learned cue
• Motion Parallax -Objects closer than our fixation point move
opposite to our direction of motion.
Objects farther away move in the same
direction as us.
Monocular Cues
• Overlap or Interposition -–Closer objects overlap objects that are
farther away
Monocular Cues
Linear
Perspective
Relative
Size
Overlap
Visual Illusions
• Reveal information about the
visual system
• Sometimes derive from
perspective cues
The Bending Lines Illusion
Repeat
Illusions
Repeat
Depth Cues
Ambiguous Images
• Have 2 interpretations, can be
switched at will
• Demonstrate the existence of topdown processing
The Schroeder Staircase
Impossible Images
• Changing perspective gradually in a
large picture can create impossible
figures (as in some Escher prints).
• If the figure is large enough, you cannot
perceive it all at once, so the change in
perspective is not readily apparent.
• Contrast the relative ambiguity of the
large and small figures on the next slide.
2 Tongs/ 3 Tongs
Another Impossible Figure
Late Vision
• Knowing more than you can see
• Informed perception
– Perceptual expectancies