Sensation and
Perception
Modules 5 & 6
What’s the difference??
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Sensation: the process by which sensory systems
and the nervous system receive stimuli from our
environment
Bottom-up processing: info processing that
analyzes raw stimuli entering through the many
sensory systems
Perception: process of organizing and
interpreting incoming sensory info
Top-down processing: info processing that
draws on expectations and experiences to
interpret incoming info
ABSOLUTE THRESHOLD
• Weakest amount of a stimulus that can be
sensed
• Has been found for vision, hearing, smell,
touch
• Varies depending on psychological and
biological factors
DIFFERENCE THRESHOLD
•AKA " just noticeable difference"
•Minimum amount of difference that can be
detected between 2 stimuli
(paint colors)
- How much do the laces on your shoes need
to be loosen so that they feel less tight?
- How much does the volume have to increase
before you can tell that your stereo has
gotten louder?
Are subliminal messages a
real thing??
Subliminal = “below threshold”
SIGNAL-DETECTION
THEORY
• Investigates the effects of the distractions
and interferences we experience while
perceiving the world
• Developed during the Cold War
• Attempts to explain & predict the different
perceptual mistakes we make
• Variables to consider:
• Stimulus variables
• Environmental variables
• Organism variables
SENSORY ADAPTATION
• Process by which we become more
sensitive to weak stimuli and less sensitive
to unchanging stimuli
• Ex: living in the city, odors, darkness at
the movie theater, temperature
Selective Attention
REVIEW
1.Define absolute threshold.
2.Give 2 examples of sensory
adaptation.
3.What is the difference between
sensation and perception?
4.What is difference threshold
also known as?
5.What is the signal detection
VISION
• Light is electromagnetic energy
• Described in wavelengths
• Light visible to humans only makes up a small
part of the spectrum
• Wavelength = color
• Amplitude = brightness
• Human photoreceptors in the eye are sensitive
to wavelengths of light energy called the visible
spectrum. (photoreceptors --> brain)
• ROY G BIV
THE EYE
• Light enters the eye and then is projected onto a
surface
• Cornea --> part of the sclera; bulge on front of
eye: focuses light by bending toward a central focal
point; protects eye
• Amount of light that enters is determined by size of
opening (pupil) in the
• colored part of our eye --> iris
• Opening --> pupil: size adjusts automatically
based on the amount of light entering eye;
sensitive to emotions
Cont…
• Once light enters the eye, it encounters the
lens
• Lens adjusts to the distance of objects by
changing its thickness
• As the light passes through the lens,
images are flipped and inverted
• These changes project a clear image of the
object onto the retina (focuses image)
So essentially….
Light travels through the pupil to the
lens and is then reflected onto the
retina. The optic nerve sends the
visual information to the brain.
RETINA CONTAINS THESE
RECEPTOR CELLS...
Rods - located in retina's periphery; sensitive only to
brightness of light; allow us to see in black & white
Cones - located in the middle of retina; involved in color
perception
Blind spot - where the optic nerve connects to the eye
and contains neither rods or cones
Activity 2.2
DEMONSTRATION
1. For the first demonstration, hold the side of the paper with the X and Y at
arm's
length while covering one eye with the other hand. If the left eye is covered,
fixate on the X (assuming it is on the left), and vice versa. Then slowly advance
the paper toward the eye. Notice what happens to the Y: At some critical
distance from the eye it disappears, but as the distance from the eye is further
decreased, it reappears. You should then be able to tune the Y in and out by
adjusting the distance of the paper from the eye.
2. The second demonstration involves using the side of the paper with the X, Y,
and Z; holding it at arm's length; fixating on the Y with the left eye covered;
and slowly advancing the paper toward the eye. At some critical distance from
the eye, the Z will disappear. If the paper is then held at this point, it is
possible to observe an unusual phenomenon: Shifting fixation to the X causes
the Y to disappear and the Z to reappear. Thus, by shifting fixation back and
forth between and Y and the X, you can make the Z and the Y alternately pop
in and out of view.
COLOR VISION
Young - Helmholtz trichromatic theory - retinas
contain 3 types of cone cells, each responding best to a
particular wavelength: blue, green, red
Opponent process theory - two-color processes,
red vs. green, yellow vs. blue, black vs. white
(complementary colors)
OPT explains afterimage p. 84
Color blindness - absence/ malfunction of cones
(monochromatic and dichromatic)
The Stroop Effect/interference
Figure 4.19
Demonstration of a complementary afterimage. Stare at the dot in the center of the flower for at
least 60 seconds, then quickly shift your gaze to the dot in the white rectangle. You should see
an afterimage of the flower—but in complementary colors.
REVIEW!!!
1. What are rods and cones?
2. Where is the blindspot located?
3. Provide one example of difference
threshold.
4. What is the stimulus for light?
5. You’re holding your dog’s leash as he
calmly lays down. Your friend comes up to
talk to you…after several minutes you
accidently drop the leash. What is this an
example of???
HEARING
VISION
HEARING
Sound is mechanical energy typically
caused by vibrating objects
Vibrations produce movement of air
molecules (sound waves)
Moving one's head helps in detecting the
source of a sound
Locating sound is automatic; in front and
behind is more difficult (uses other
CHARACTERISTICS OF SOUND
Frequency - corresponds to pitch; measured in hertz
(Hz) [vocal chords - more cycles = higher pitch]; 2020,000 Hz
Amplitude - corresponds to loudness; measured in
decibels (dB); 0 dB threshold = ticking of a watch 20 ft
away in quiet room
THE EAR
Outer/middle/inner
Pinna - visible skin/cartilage
Auditory canal --> eardrum (tympanic membrane)
Eardrum - gateway to the middle ear; thin
membrane that vibrates when sound waves strike
it (damage)
Ossicles - located in the back of the eardrum; 3
small bones that pick up and transmit vibration
1. Hammer
2. Anvil
Cont…
Cochlea - inner ear; fluid-filled, snail-shaped
bony tube
Vibrating fluid stimulates hair cells --> tiny
projections in cochlea that are receptor cells for
hearing
Energy is converted to neural impulses that are
transmitted to the brain via auditory nerve -->
projected to hearing areas of cerebral cortex
(temporal lobe)
DEAFNESS
2 million people are deaf
Conductive deafness - sound waves are unable
to be transferred from the outer ear to inner ear;
damage to the ossicles (middle ear) – unable to
vibrate (hearing aids)
Sensorineural deafness - damage to the inner
ear or hair cells in the cochlea (disease or trauma);
people are unable to hear certain frequencies
Activity 2.3
REVIEW
1. What determines loudness? How is it measured?
2. How do we SEE? Describe the process, listing the parts
involved.
3. How do we HEAR? Describe the process, listing the parts
involved?
4. How do we see in color?
5. What is an afterimage? What theory describes this
phenomenon?
6. What is the smallest bone in the body?
7. What takes information from the eye to the brain?
8. Where does auditory information go to in the brain? (What
lobe???)
9. What is the stimulus for vision? For hearing?
10.Describe 2 types of deafness.
SMELL
Starbursts!
Molecules are given off by substances
Olfactory cells carry it to the olfactory bulb, which activates
the prefrontal cortex  amygdala/hippocampus
Olfactory nerve sends info to brain
Odors can evoke highly emotional memories
Women detect odors more readily than men; brain responses
to odors are stronger in women
Pheromones - same-species odors, form of chemical
communication
Anosmia - loss of sense of smell
TASTE
Also known as gustation
Receptor cells are located in the taste buds
Receptors are sensitive to 4 basic taste qualities:
1. Salty
2. Sweet
3. Sour
4. Bitter
5. Umami
Receptor cells reproduce rapidly enough to completely renew
in a week
1/4 of population are "supertasters"
TOUCH
Skin senses pressure, temperature, and pain
Touch is vitally important to infants and elderly
Pressure --> hair
Temperature --> relative
Pain --> prostaglandins are chemicals that help body
transmit pain messages to the brain (aspirin curbs
production); endorphins block release
PAIN
Message sent to spinal cord to thalamus then projected
to cerebral cortex which registers the location and
severity
Gate-control theory - only certain amount of info can be
processed by nervous system at a time
Pain messages travel on one set of nerve fibers in spinal
cord, and all other sensory messages travel along another
set
Fibers carrying pain messages have pain gates that open
Non-pain fibers can close gates if there is a competing
stimulation to larger nerve fibers (rubbing/icing)
BODY SENSES
Vestibular sense - located in your inner ear
Provides information about your overall orientation
Relies on fluid-filled semicircular canals in ear
Concerned with balance and body position
Kinesthesis - communicates information about
movement and location of body parts; relies on receptors
in muscles and joints (touch nose/"falling asleep")
Activity 3.1 – Sensory Interdependencies
Perception
http://www.youtube.com/watch?v=-yl0HGD7B20
“Maybe each human being lives in a unique world, a private
world different from those inhabited and experienced by all
other humans. . If reality differs from person to person, can we
speak of reality singular, or shouldn't we really be talking about
plural realities? And if there are plural realities, are some more
true (more real) than others? What about the world of a
schizophrenic? Maybe it's as real as our world. Maybe we
cannot say that we are in touch with reality and he is not, but
should instead say, His reality is so different from ours that he
can't explain his to us, and we can't explain ours to him. The
problem, then, is that if subjective worlds are experienced too
differently, there occurs a breakdown in communication ... and
there is the real illness.”
― Philip K. Dick
PERCEPTION
Gestalt (remember this???) - the whole experience is
greater than the sum of the individual parts; we don’t
focus on individual stimuli in our environment – we
group them into more meaningful units
Closure - tendency to perceive a whole figure even if
there are gaps
http://www.youtube.com/watch?v=nxKcpfFvuf8
Closure
A Gestalt
PERCEPTION
Figure-ground perception - perception of figures
against a background
Grouping Principles: proximity, similarity, continuity,
common fate
Perception of movement - relative; waiting at a light
Stroboscopic motion - drawing books, movies; law of
continuity - prefer to see things as one continuous image
Figure-ground Perception
Figure-Ground
Grouping Principles
DEPTH PERCEPTION - PERCEIVED
BY USING A NUMBER OF CUES
Monocular cues - depth cues provided by one eye
Motion parallax
Texture gradient
Shadow
Overlapping/interposition
Clearness
Linear Perspective
Binocular cues - depth cues provided by both eyes
Retinal disparity
Convergence
Monocular cues
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Motion Parallax
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Texture Gradient
Monocular Cues
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Shadow
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Overlapping
Interposition
Monocular Cues
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Linear Perspective
Binocular Depth Cues: Finger Sausage
VISUAL ILLUSIONS
Perceptual illusions occur when sensory stimuli are
misinterpreted; reveal the strategies we use to interpret
sensations correctly
Muller-Lyer
Ponzo
The Ames room
Muller-Lyer
Ponzo
Size Distance Relationship
Size Distance Relationship
Size Distance Relationship
PERCEPTUAL CONSTANCY
Size
Shape
Lightness
Perceptual Constancies