UNIT 4, Sensation and Perception Notes, pp. 115-173
(Updated for 2011; these go with Chapters 5 and 6 in 2007 book)
Prosopognosia, face blindness, page 115
What are sensation and perception? What do we mean by bottom up and top down
processing?
116: Sensation is referred to as bottom up processing: from the senses up to the brain;
this is when we have no prior knowledge of something and we start at the bottom.
Perception is top down processing: higher level function where you draw conclusions;
we apply prior knowledge to something
An example is stereotyping someone. We apply what we already know about the
characteristics and make a judgment even though we don’t know them. Stereotyping
does help because it is a mental short cut and we need to make them every day, for
certain stimuli, on a regular basis in order to navigate our world.
Selective Attention, 117
How are we affected by selective attention?
Selective attention you focus on only one stimulus in the environment
People with ADHD have difficulty with this; they can’t tune anything out and take it all
in.
a. Cocktail party effect focusing on one voice in a crowd at a party, for example
b. Unnoticed stimuli still has an effect on you: example, women who were played a
tune that they didn’t pay attention to still preferred it later
c. Cell phone drivers have more accidents. Even pedestrians on cell phones are less
safe.
Selective Inattention, 118
c. inattentional blindness Neisser, Becklen and Cervone in their experiment people did
not notice a woman walking across a basketball court because they were directed to count
the number of times black shirt players passed a ball.
This kind of blindness is defined as failing to see objects when our attention is directed
elsewhere.
Simons and Chabris did a replication in 1999. See fig. 4.2
Other examples of inattentional blindness:
Change blindness lack of attention to changing events or images in a scene; for
examples see Fig 4.3
Change deafness failing to recognize a change in the way a person is speaking when the
words are difficult
Choice blindness not recognizing a change in the choice you have made
The pop-out phenomenon when a strikingly distinct image jumps out and gathers our
attention
What are the absolute and difference thresholds? Do stimuli below the threshold have any
influence? 120
Psychophysics: the study of the relationship between physical characteristics of stimuli
and the psychological perception of them
Absolute threshold: the lowest amount of a stimulus to notice it 50% of the time
Gustav Fechner did early research on this topic.
Ex.: turning down the radio volume so that you only notice the faint sound half the time
Thresholds increase with age.
Signal Detection theory: arousal, expectations, experience and motivation all affect
whether or not you detect a stimulus
Subliminal stimulus: any stimulus below your absolute threshold
Ex: a microscopic cell that you cannot see with your naked eye
We can be influenced by information just below our threshold. An image or word can
prime our response to a later question. We can feel what we do not know and
experience responses to imperceptibly brief stimuli. This is due to context effects.
Subliminal advertisements do have an affect on you, but do not persuade you. The FCC
banned them in 1974 after a James Vicary claimed to have influenced movie goers with
subliminal messages in a movie.
Greenwald conducted 16 studies about subliminal self-help programs and found no
effect.
The difference threshold is the lowest difference you can detect between two stimuli 50%
of the time. 122
Aka just noticeable difference, jnd
Ex: noticing the difference between 1 kg. And 1.02 kg 50% of the time
Weber’s Law: two stimuli must differ in percentages or ratios or proportions for a person
to notice it
Sensory adaptation,123
What is the function of sensory adaptation?
Lowered sensitivity due to constant pressure from a stimulus
Ex: you go into someone’s house and notice a smell, but this only lasts for a while
because sensory adaptation allows you to focus on other stimuli
Ex: you notice your foot in contact with the floor, but then move on to other stimuli
We focus on informative changes in our environment.
We perceive the world as it is useful for us to perceive it.
II. Vision p. 124
What is the energy we perceive as visible light?
Transduction: sensory energy is converted/transformed into neural energy
The Stimulus Input: Light Energy
Wavelength: distance between peaks determines hue (the color we see) of light
Amplitudes: Height of wave; Intensity (influences brightness) and loudness
Acuity: normal, nearsightedness, farsightedness
A. Parts of the eye
How does the eye transform light energy into neural messages?
Pupil adjusts the opening
Iris muscle regulating pupil
Lens structure behind pupil that changes shape to focus images on the retina
Accommodation: lens changes shape to focus near or far objects on the retina
Retina has 125 million rods (detect brightness) and 6 million cones (detect color)
REVIEW TABLE 4.1 ON PAGE 128
Optic nerve: carries neural impulses from the eye to the brain
Receptive fields: collection of rod and cone receptors that funnel signals to a particular
visual cell
Lateral antagonism: affect on neighboring receptive fields
Acuity: sharpness of vision
Nearsightedness light rays are focused in front of the retina
Farsightedness light rays are focused behind the retina
Path of vision information: rods/cones to bipolar cells to ganglion cells to optic nerve
Ganglia: cells in the retina that generate action potentials
Photoreceptors: nerve cells in the retina that code light energy into neural activity
Optic disc: hole in the retina where the optic nerve exits the eye: no receptors there…
Blind spot: there are no receptor cells where the optic nerve leaves the retina, but the two
eyes compensate for each other’s blind spot, plus our eyes are constantly moving
Fovea: light is centrally focused here where there are only cones; see figure 4.10
Light travels to the back of the retina and enters rod and cones; the next process is a
chemical reaction in bipolar cells; finally, ganglion cells become active; their axons
connect with the optic nerve before the information is sent to the brain for processing.
B. Visual information processing p. 128
How does the brain process visual information?
Hubel and Wiesel discovered Feature detectors: sensitive to specific features we see. The
information is then sent to other cortical features where “supercell clusters” interpret the
data.
Parallel processing: processing lots of information at the same time; page 130, see fig.
4.15
Computers use serial processing
Recognizing a face requires 30 percent of your cortical brain power (ten times what you
need to perceive sounds)
Example: seeing an orange and recognizing the color, round shape and bumpy texture
Blind sight: you cannot perceive the object but you can locate it. The neural areas that
bring vision into awareness are impaired.
Visual information process stages:
Retinal processing
Feature detection
Parallel processing
Recognition (see fig. 4.16)
C. Color vision 132
What theories help explain color vision?
Chromatic v. achromatic (color v. black and white)
Young-Hemholtz trichromatic theory of color vision: light is detected by three types of
cones sensitive to red, blue and green
Evidence for theory: color blindness: see figure 4.17, page 132
Subtractive color mixing for paints: the more colors you add, the fewer that are reflected
back; red, blue and yellow equal black
Addititive color mixing with paints: adding more colors leads to more light waves
becoming white
Opponent process theory: (Ewald Hering, Jameson, Hurvich) color is then processed by
opponent colors.
Example: yellow is inhibited and blue is exhibited
Evidence for: negative after image; see fig. 4.18
Combined theory: color processing occurs in two stages:
a. retina’s red, green, and blue cones respond to different color stimuli
b. their signals are processed by the nervous system’s opponent process cells en
route to the visual cortex
Color constancy you perceive the color as same even as the amount of light differs
III. Hearing (Audition) 134
Frequency: number of waves per second
Pitch: a tone’s highness or lowness
Decibels: measuring unit for sound energy
Audition: sound is converted into neural impulses
Outer ear: auditory canal
Middle ear: ear drum; hammer, anvil, stirrup these vibrate when ear drum is stimulated
Inner ear: cochlea and basilar membrane: vibrations cause the cochlea’s membrane to
vibrate, jostling the fluid that fills the tube. This causes ripples in the basilar membrane,
bending hair cells lining its surface. The hair cell movement triggers impulses in
adjacent nerve cells, whose axons converge to form the auditory nerve. Neural messages
are then sent to the temporal lobe’s auditory cortex. See fig. 4.19, page 135
Hair cell damage leads to most hearing loss.
Perceiving Pitch, 137
What theories help us understand pitch perception?
Hermann von Helmholtz’s Place theory: we hear different pitches because a different
place in the cochlea is stimulated
Frequency theory: the speed of neural impulses matches the speed of the sound wave
The direction of sound: directly in front or behind sounds are more difficult to locate; we
locate sounds by the timing of the arrival of the sound waves to our ears
Volley principle neural cells alternate firing in rapid succession to achieve a combined
frequency of 1000 times per second
Place and frequency theory combine to explain intermediate pitches
Locating Sounds, 138
How do we locate sounds?
One ear hears the sound as more intense and sooner.
Hearing loss and deaf culture 138
What the common causes of hearing loss, and why does controversy surround cochlear
implants?
Conduction deafness: damage to ear drums or bones causes loss of hearing
Nerve deafness (sensorineural hearing losss) damage to cochlea, hair cells or basilar
membrane causes loss of hearing; may lose sensitivity to different tones; the hearing loss
is uneven and not total
Conductive deafness: problems disrupt the conduction of sound through the outer and
middle ear affecting hearing before the sound reaches the cochlea and the nerve receptors
of the inner ear.
Cochlear implants
author.
a bionic ear for nerve deafness; said to be controversial by the
Sensory compensation
Lacking one sensation people can compensate using other senses
Example: aphasics can read lying behavior: they can’t speak but focus more on facial
cues, voice and body movements
IV. Other important senses p. 141
A. Touch
How do we sense touch and sense our body’s position and movement? How do
we experience pain?
Composed of four senses: warmth, pain, cold, pressure (the only one with identifiable
receptors)
Warm + cold = hot
Pressure + cold= wet
Pressure + pain= tickling itch
Hairy skin: contains hair cells which detect movement and pressure
Glabrous skin: no hair cells; hands, feet, lips; more sensitive
Rubber hand illusion: fig. 4.23
Kinesthesis: sense of position and movement of your body parts the sensors are in the
muscles, joints and tendons
Ian Waterman lost this sense. Uses his sense of vision to move; has difficulty in
darkness.
Vestibular sense: fluids in the semicircular canals, vestibular sacs, and cochlea detect
body position, motion and balance
Propioception: loss of ability to move unless you can see yourself move
Phantom Limb: recepting neurons still fire resulting in “feeling” in a nonexistent limb
What is Pain? Page 145
Ashlyn Blocker can’t feel pain
Nociceptors: these detect harm to the body
Gate control theory Robert Melzack and Patrick Wall: the spinal cord has gates that
open or close to transmit pain messages
Small fibers open to transmit pain; large fibers close to block pain
Endorphins: natural pain killers
Phantom limb sensations 7/10 amputees have feelings in missing limbs
Phantom sounds, the sound of silence, tinnitus
Pain physical and psychological interpretations that can be distracted; V.S.
Ramachandran experiment: a variation of the rubber hand illusion
Biopsychosocial model of pain, fig. 4.25:
Nerve activity, brain interpretations, expectations, presence of others all influence pain
Controlling pain, 145
Some believe hypnosis can reduce pain; others say it merely distracts the mind; see Unit
5
Placebos are used to great effect; example Acupuncture
Exercise and electric stimulation also ease pain
Fire walking: based on heat diffusion, the hot wood was a poor heat conductor
Lamaze: relaxation, counter stimulation and distraction method used for child birth
B. Taste Gustatory sense p. 146
How do we experience taste?
Is a chemical sense of sweet, sour, salty, bitter and umami (a meaty taste) table 4.2
Bitter or sour plants are often toxic, while sweet ones are often nutritious
Taste buds generate every 1-2 weeks but smoking, alcohol and drinking all lower
sensitivity
Supertasters (Linda Bartoshuk research) they have more fungiform papillae and feel
more pain from lesions on the tongue or from other irritants; and they are better at
perceiving fat in food
Expectations also influence taste
Sensory interaction P. 148
When you cannot distinguish apple v. potato, for example, without tasting AND smelling
Also influences what we hear:
McGurk Effect (p. 148) seeing someone say something, while hearing another sound,
leading to the perception of a third blending of the other two
Synaesthesia p. 148: one sensation produces another: “hearing” a color or “tasting” a
number
B. Smell or Olfaction p.148
How do we experience smell?
Olfactory bulbs, olfactory cilia see figure 4.28
The chemical information goes from the nose directly to the temporal lobe.
This is the only sense not first transmitted to the thalamus for processing; instead going to
the olfactory brain, see figure 4.30 on page 150
Dogs have many times more olfactory receptors.
Pheromones: A chemical secreted externally by an organism to send information to
members of the same species.
Males and females (gender) can be identified based on odor alone.
People come to like scents associated with good experiences.
Smell and memory: areas that process memories and smells are connected by brain
circuitry.
Perceptual Organization, 151
How did the Gestalt psychologists understand perceptual organization?
a. Visual capture when senses compete with one another, vision captures and
overwhelms the others
Examples:
1. Where does sound come from in a theater v. where is it perceived?
2. A ventriloquist
Gestalt is an organized whole: we have a tendency to perceive the environment of pieces
in terms of the big picture
Form perception, 151
How do figure-ground and grouping principles contribute to our perceptions?
a. Figure is the object we focus on; Ground is the background in the environment
b. Figure-ground: humans have a tendency to organize their perception so that an
object of focus is separated from the background fig. 4.32 (a tessellation, also
called a repeating geometric pattern)
c. Grouping: these are perceptual rules we follow (see visuals on p.152)
i. Proximity items close together are viewed as being together(when someone we don’t
know walks with us, can make us uncomfortable)
ii. Closure
iii. Connectedness
iv. Similarity if they look the same they are grouped together (but what about when
someone you don’t know wears exactly the same outfit?)
v. Continuity
Depth perception, 153
How do we see the world in three dimensions?
partly innate; it allows us to see 2D images in 3D
Visual cliff, fig. 4.35
Gibson & Walk, 1960, placed kids on a visual cliff (age 6-14 mos.); most refuse
indicating depth perception
Binocular cues: you need both eyes to perceive the depth levels
1. Retinal disparity: binocular cue in which the greater the disparity the farther the
image is away
Another binocular cue to distance is Convergence monocular cues; the more eyes turn
inward, the closer the object
h. Monocular cues: distance cues that are available to either eye
Gateway Arch is a horizontal vertical illusion; fig. 4.37
Examples (see page 155)
Relative size if two objects seem similar in size, the smaller one is assumed by the eye
to be farther away
Interposition, if one object blocks our view of another we assume it is closer
Relative clarity, we perceive hazier objects as farther away
Relative height, objects higher in our field of vision are assumed to be farther away
Relative motion or Motion parallax a depth cue whereby the difference in the
apparent rate of movement of different objects gives you information about the
relative distance of the objects; for example objects that would be nearer to you
would speed across your visual field
Texture gradient, if the texture goes from coarse to fine, distance is perceived as
greater
Linear perspective, the more parallel lines converge the greater the perceived distance
Light and shadow nearer objects reflect more light to the eye
Relative brightness
Amblyopia: lazy eye
Strabismus: deflected eye; crossed eyes)
Motion perception, 155
How do we perceive motion?
We compute motion by assuming objects moving away are getting smaller
Stroboscopic movement: we view rapidly moving similar objects are representing
movement
Phi phenomenon perception of movement when lights blink one after another (Max
Werthheimer observed this)
Apparent motion the illusion of movement in a stationary object; it illustrates higher
level processing in the brain; movies and TV are examples where the brain creates
apparent motion from still pictures
Induced motion illusion when you’re tricked into seeing movement: looking up at the
sky on a cloudy night you “see” the moon move through the clouds; the frame of
reference is wrong
Motion after effect: occurs when you gaze at a moving object for a long period of time
then look at something stationary; the new thing appears to move in the opposite
direction; also called the waterfall effect; this is evidence that motion-sensitive neurons
exist in the visual cortex at the back of the brain
Perceptual constancy, 156
How do perceptual constancies help us organize our sensations into meaningful
perceptions?
Linear perspective can cause you to see one object as bigger even when they appear to
be the same size
Shape and size constancies
Objects remain constant in shape or size even as our distance from them changes
Size distance relationship
Examples:
Moon illusion: can look up to 50% greater on the horizon; monocular cues for distance
are responsible for this; see the other examples on page.
Ponzo illusion; fig. 4.42
Also see the Ames room illusion on page 157, fig. 4.43
Lightness constancy, AKA brightness constancy, 158, see figure 4.44
Depends on relative luminance, the amount of light an object reflects relative to its
surroundings
Color constancy
We see color due to how our brain interprets the light reflected by the object relative to
its surrounding objects (there is no color intrinsic to the object)
IV. page 159 Perceptual Interpretation
Philosopher John Locke argued that perception develops through learning from
experience
Infancy is a critical period of development (see Unit 9 for background)
Patients who had been blind can’t recognize objects by touching them
Sensory deprivation and restored vision
What does research on sensory deprivation and restored vision reveal about the effects on
experience on perception?
Sensory restriction does no damage if it occurs later in life
Perceptual adaptation the ability to adjust our vision for artificial displacement
How adaptable is our ability to perceive?
George Stratton wore upside down goggles for eight days before adapting.
Example: the quarterback on the Sensation and Perception video
c. Sperry eye experiments: he surgically turned eyes of animals; mammals can
adapt/reptiles cannot
Perceptual set, created by experiences, assumptions, expectations
How do our expectations, contexts and emotions influence our perceptions?
Example: a mental, or perceptual, set causes you to see one thing and not another;
explains UFOs---seeing them and not the actual natural phenomena
Also see figure 4.47 on p. 161
Perceptual sets are determined by schemas, concepts that organize information; schemas
can “prime” us to see certain things and not others; Jean Piaget (see Unit 9) developed
this concept.
Context effects, 162
A later stimulus can determine how we perceive and earlier one
Emotion and motivation
Expectations influence perceptions in a top-down manner
Perception is a biopsychosocial phenomenon: senses, attention, schemas, cultural
assumptions, expectations all play a role
Extra Sensory Perception
What are the claims of ESP, and what have most research psychologists concluded after
putting these claims to the test?
50% of Americans believe in
The claims of ESP: the information does not come from the five senses, thus extra
sensory
Parapsychology the study of paranormal phenomena
Most scientists are skeptical.
Concepts: see figure 4.53 for relationships between the following terms:
Telepathy sending thoughts
Clairvoyance perceiving an event with no prior knowledge or sensory experience
Precognition seeing future events
PK psychokinesis moving objects with mental powers
Vague predictions are often interpreted later to have meaning
Correlations are often assumed to be causally connected
Confirmation bias occurs when the believer only finds evidence that supports their claim
and ignores all the evidence that refutes it.
No reproducible experiment has supported ESP
35% of major city police departments have used psychics, but none have had success.
Magician James Randi offers $1 million to anyone who can demonstrate a psychic power
under scientific testing. No one has passed the preliminary test to make it to final
testing. www.randi.org
Other groups offered 200,000 euros, with no winner.
Why do people believe in ESP, when there is no evidence?
1. Misperceptions
2. Misinterpretations of results
3. Selective recall
Key terms to know on page 172
AP quiz on page 173
Perception and the Human Factor, Appendix B13-15
Human factor psychologists help design machines humans can better use
How do human factors psychologists work to create user-friendly machines and work
settings?
Norman has a website for good design (www.jnd.org)
Research on human error in aircraft accidents: distance cues confused pilots into thinking
they were higher than actual; caused by night and lack of visuals in front of the land strip.
Action statements work best in directing behavior
Assistive listening technologies
Loop systems broadcast right into the hearing aid
Technology designers mistakenly assume others know enough about their device;
simulating what it’s like not to know is called, the curse of knowledge.