Sensation and Perception Chapter 6. Sensation vs. Perception Psychophysics: The study of the relationship between physical stimuli and our experience.
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Sensation and Perception
Chapter 6
Sensation vs. Perception Psychophysics: The study of the relationship between physical
stimuli and our experience of them. Sensation
The experience of sensory stimulation “I see…hear…feel…smell…taste something”
Perception Creating meaningful patterns from raw sensory information “I see a cat;” “I hear footsteps” etc.
Bottom-Up Processing (DATA-DRIVEN) Beginning with stimulation of our senses, we interpret
sensory information with our brains I see a furry, 4-legged creature with a tail and identify this as
a dog Top-Down Processing (SCHEMA-DRIVEN)
Using our schemas, expectancies and past experiences, we interpret sensory information to construct deeper meaning
The dog is growling and foaming at the mouth and I realize it may have rabies so I will not approach it
Demo 1: Top-Down Processing
Based on research of Bugelski and Alampay (1961)
Examine the series of images on your worksheet. Afterwards, look at the image below and describe what you see in the space on your worksheet.
The Nature of Sensation
The Basic Process Receptor cells
Specialized cells that respond to a particular type of energy
These exist in your sense organs
Law of specific nerve energies (Muller) One-to-one relationship
between stimulation of a specific nerve and the resulting sensory experience
For example, applying pressure with your finger to your eye results in a visual experience – try it!
Press on your
eyeball und you vill have a visual
experience…
YA!
Ich bin Johannes Muller!
Sensory Thresholds Absolute threshold (Demonstration #2)
The minimum amount of energy that can be detected 50% of the time
E.g. At what point can you hear the presence of a sound? Some examples for humans:
Taste: 1 gram (.0356 ounce) of table salt in 500 liters (529 quarts) of water
Smell: 1 drop of perfume diffused throughout a three-room apartment
Touch: the wing of a bee falling on your cheek from a height of 1cm (.39 inch)
Hearing: the tick of a watch from 6 meters (20 feet) in very quiet conditions
Vision: a candle flame seen from 50km (30 miles) on a clear, dark night
Sensory Thresholds Sensory adaptation (Demonstration #3)
An adjustment of the senses to the level of stimulation they are receiving
Sandpaper demonstration? toothpaste/orange juice phenomenon? Distortion goggles – in springtime…
Difference threshold (Demonstration #4) The smallest change in stimulation that can be detected 50%
of the time Also called the just noticeable difference or JND e.g. At what point can you tell that the TV volume has been
raised? Weber’s Law
States that the difference threshold is detected by a constant minimum percentage of the stimulus, not a constant amount
e.g. to detect a difference in weight, the change must be 2% of the original stimulus’ weight
Subliminal Perception? We know that below threshold (subliminal) stimuli bombard
us regularly… BUT…do we respond to these stimuli that are below our
level of awareness? Research shows that the effect only occurs in controlled
laboratory studies Research outside the laboratory shows no significant, lasting
effect of subliminal information Priming
The often unconscious activation of certain associations for the purpose of altering perception, memory or response
Individuals flashed a pleasant or unpleasant image before viewing a photo of a person were influenced to judge the person positively if they saw a pleasant picture and negatively if unpleasant
Subliminal Research at Duke University Subliminal Advertising Experiment (Demo #5)
A Challenge to Sensory Thresholds?
Signal Detection Theory challenges the notion of the absolute threshold.
SDT is a mathematical model that predicts how and when we will detect the presence of a faint stimulus or signal There is NO single absolute threshold Detection of a stimulus depends on a person’s experience,
expectations, motivations, and fatigue.
Vision
EYE see you!
I cannot, however
Vision: Transduction and Light Energy
Transduction: Our eyes have the ability to convert one form of energy – in this case LIGHT – into messages that our brain can interpret as a visual experience
We can only see a small part of the electromagnetic spectrum (see diagram on reverse of absolute threshold)
Properties of Color and Light Energy Hue
Colors we see such as red and green
Determined by wavelength
Shorter wavelength results in blue-violet; longer results in red
Brightness “loudness” or intensity
of a color Determined by
amplitude Saturation
Vividness of a hue
The Visual System Cornea
Transparent protective coating over the front of the eye
Pupil Small opening in the iris
through which light enters the eye
Iris Colored part of the eye;
controls size of pupil Lens
Focuses light onto the retina Changes shape through
accommodation to help focus image on retina
Retina Lining of the eye containing
receptor cells that are sensitive to light
Fovea Center of the visual field
Receptor Cells Cells in the retina that are
sensitive to light Visual receptors are called rods
and cones Rods
About 120 million rods Respond to light and dark Very sensitive to light Provide our night vision
Cones About 8 million cones Respond to color as well as light and
dark Work best in bright light Found mainly in the fovea
Marker Demonstration? Stars in the sky?
Receptor Cells Bipolar cells
Receive input from receptor cells
Ganglion cells Receive input
from bipolar cells Axons of these
cells form optic nerve
Blind spot Area where
axons of ganglion cells leave the eye
NO RECEPTORS! Blind-spot demo
Click for animated visual process!
From Eye to Brain Optic nerve
Made up of axons of ganglion cells
carries neural messages from each eye to brain
Optic chiasm Point where part
of each optic nerve crosses to the other side of the brain
Thalamus relays sensory info to visual cortex in occipital lobes
Feature Detection Feature detectors are neurons in the brain that
respond to specific aspects of a stimulus: edges, lines, movements, angles Feature detectors in the visual cortex send signals to
other areas of the cortex for higher-level processing These areas – called supercell clusters – work in teams
to determine familiar patterns – such as faces (processed in the right-side of temporal lobe)
Parallel processing Our brains process multiple features of visual experience
at one and integrate these features to create our experience of vision
If parts of this integration are disrupted through damage or electromagnetic pulses, we may lose our ability to processes certain aspects of vision such as movement or lines (blindsight)
Theories of Color Vision Additive color mixing
Mixing of lights of different hues Lights, T.V., computer monitors (RGB) Lights add wavelengths
Subtractive color mixing Mixing pigments, e.g., paints Pigments absorb or subtract wavelengths
Theories of Color Vision Trichromatic theory (Young-
Helmholtz) Three different types of cones
Red Green Blue
Experience of color is the result of mixing of the signals from these receptors
Can account for some types of colorblindness
Approximately 10% of men and 1% of women have some form of “colorblindness” (sex linked trait)
Dichromats: Two colors only Monochromats: One color only Ishihara Test
Theories of Color Vision Trichromatic theory cannot explain all aspects of
color vision People with normal vision cannot see “reddish-green” or
“yellowish-blue” Red-Green colorblind people can see yellow, which
Helmholtz argues is a result of red and green cones firing – if Helmholtz is correct, how could this be?
Color afterimages? Opponent-process theory (Ewald Hering)
Three pairs of color receptors Yellow-blue Red-green Black-white
Members of each pair work in opposition Can explain color afterimages
Both theories of color vision are valid
Adaptation Dark adaptation
Increased sensitivity of rods and cones in darkness
Light adaptation Decreased sensitivity of rods and cones in
bright light Afterimage
Sensory experience that occurs after a visual stimulus has been removed in response to overstimulation of receptors
Color Vision in Other Species Other species see colors differently
than humans Most other mammals are
dichromats Rodents tend to be monochromats,
as are owls who have only rods Bees can see ultraviolet light Stomatopods have the most
complex color hyperspectral vision in the animal kingdom, allowing them to differentiate between colors that may appear the same to other human and non-human animals.
The Mantis Shrimp is a stomatopod with hyperspectral vision. Hyperspectral capabilities enable the mantis shrimp to recognize different types of coral, prey, or predators.
I’m neith
er shrimp nor mantis…I am
mantis
shrimp.
Hearing
Ear we go!
Sound We hear by transduction of
sound waves into nerve impulses.
Sound waves Changes in pressure caused
by molecules of air moving Frequency
Number of cycles per second in a wave, measured in Hertz (Hz)
Frequency determines pitch Amplitude
Magnitude (height) of sound wave
Determines loudness, measured in decibels (dB)
Overtones Multiples of the basic tone
Timbre (TAM-ber) Quality of texture of sound
The Ear Outer Ear
Pinna Tympanic
Membrane (eardrum)
Middle Ear Contains three
auditory ossicles (bones)
Malleus (Hammer)
Incus (Anvil) Stapes (Stirrup)
These bones relay and amplify the incoming sound waves
Inner Ear Oval Window set in motion by
ossicles Fluid-filled Cochlea Basilar membrane set in motion by
the rippling fluid Organ of Corti sits atop the basilar
membrane and contains with cilia (hair cells) which bend as basilar membrane vibrates
Ear to Brain Cilia send nerve impulses
through the auditory nerve to the brain
Auditory nerve Connection from ear to
brain Provides information to
both sides of brain Information processed
in auditory cortex in temporal lobe
Theories of Hearing Loudness is determined by how many hair cells fire Theories of Pitch
Place theory Herman von Helmholtz (again!) Pitch is determined by location of vibration along the basilar
membrane Frequency theory
Pitch is determined by frequency hair cells produce action potentials
Volley Principle Accounts for high-frequency (high pitched) sounds Pattern of sequential firing determines pitch where hair cells in
teams: some fire while others go through refractory Sound Localization
Binaural cues allow us to determine source of sound Interaural Time Difference (ITD) says nearer ear picks up
sound first to provide clues about sound source Sounds directly behind us are most difficult – no visual cues
and little to no ITD.
Hearing Disorders About 28 million people have some form of hearing damage
in the U.S. Can be caused by
Injury Infections Explosions Long-term exposure to loud noises
Conduction hearing loss results from damage to parts of the ear itself
Sensorineural hearing loss results when there is damage to hair cells or auditory nerve
Cochlear implants can replace damaged hair cells and transduce sounds into electrical signals sent to the auditory nerve Use of the implants is debated Many advocates for the deaf argue that deafness is NOT a
disability, but rather an enhancement of other senses
The Other Senses
The Skin Senses Skin is the largest sense organ There are receptors for
pressure, temperature, and pain
Touch appears to be important not just as a source of information, but as a way to bond with others
Homunculus Man Proportional representation of skin
receptor concentration The larger the part, the more
receptors/the more sensitive Demo: Skin sensitivity
“Paradoxical heat”
Remember Me?
Kinesthetic Senses Kinesthetic senses
provide information about the position and movement of body parts Stretch receptors
sense muscle stretch Golgi tendon organs
sense movement of tendons when muscle contracts and send impulses to CNS
Vestibular Senses Vestibular senses provide
information about equilibrium and head and body position Fluid moves in two
vestibular sacs and the semicircular canals
These vestibular organs are lined with hair cells that bend when fluid moves over them
Vestibular organs are also responsible for motion sickness
Motion sickness may be caused by discrepancies between visual information and vestibular sensation
Pain Serves as a warning about
injury or other problem Large individual differences in
pain perception Gate control theory
Neurological “gate” in spinal cord which controls transmission of pain to brain
Major pain signals (large fiber activity) can close “gate” while small ones open it
Biopsychosocial theory Holds that pain involves not
just physical stimulus, but psychological and social factors as well
Placebo effect Shows that when a person
believes a medication reduces pain, their pain is often reduced even though no medication was given
Pain relief is likely the result of endorphin release
Alternative approaches Hypnosis and Self-hypnosis Acupuncture Thought distraction
Taste Five Basic Tastes Traditionally, taste sensations consisted of sweet, salty, sour,
and bitter tastes. Recently, receptors for a fifth taste have been discovered called “Umami”
Sweet Sour Salty Bitter Umami(Fresh [dead?]
Chicken)
Taste Receptor cells are
located in taste buds
Taste buds are located in papillae (“pa-PILL-ee”) on the tongue
Chemicals dissolve in saliva and activate taste receptors inside the taste buds
Taste is processed in the parietal lobe
Taste Why do we have
receptors for the tastes we do?
Evolutionary perspective on how taste receptors developed?
Other aspects of taste result from the interaction of taste and smell together, such as flavors.
Without a sense of smell, our ability to distinguish flavor vanishes!
Smell Detecting common odors
Odorant binding protein (OBP) is released and attached to incoming molecules
These molecules then activate receptors in the olfactory epithelium
Axons from those receptors project directly to the olfactory bulb
Women have a better sense of smell than men
Anosmia Complete loss of the
ability to smell
Smell, Taste and Memory The brain region for
smell (in red) is closely connected with the brain regions involved with memory (limbic system). That is why strong memories are made through the sense of smell.
Smell and Pheromones Pheromones
Used by animals as a form of communication
Provides information about identity
Also provides information about sexual receptivity
Pheromones stimulate the vomeronasal organ (VNO)
Information from the VNO is sent to a special part of the olfactory bulb used for pheromonal communication
T-Shirt Study?
Perception How do we
integrate our sensory experiences into something meaningful?
Gestalt principles
Perceptual Organization: Figure Ground We perceive a foreground object (figure) against a
background (ground) Animals may look like the background they inhabit
as a way of destroying figure-ground distinction
Perceptual Organization:Grouping
Closure (above) : We fill in gaps to complete a whole object and assume there are three circles and two triangles in this picture.
Proximity: We group nearby things together
Similarity: We group together objects that look alike
Continuity: We tend to perceive smooth and continuous patterns over separate pieces
Connectedness: We group together things that are connected as one unit
Perception of Distance and Depth Visual Cliff revisited Binocular cues – those
that require both eyes Stereoscopic vision Retinal disparity Angle of Convergence Hotdog Finger Illusion?
Perception of Distance and Depth
Monocular cues – those that require only one eye Relative height Relative size Interposition Linear perspective Relative motion
(motion parallax) Light and shadow Texture gradient
Localizing Sounds We use both monaural
and binaural cues Loudness
Louder sounds are perceived as being closer
Time of arrival Sounds will arrive at
one ear sooner than the other (ITD)
This helps determine direction of the sound
Perception of Movement Apparent movement
Illusion that still objects are moving
Autokinetic illusion Perceived motion of a
single object without any grounding references
Stroboscopic motion Created by a rapid series of
still pictures Phi phenomenon
Apparent motion created by lights flashing in sequence
Perception of Movement
Perception of Movement
When one analyses step-by-step the gray levels next to the spokes, there are two steps where any given spoke first merges with the preceding sector on one side, then with the succeeding sector. Since in this transition the spoke’s identity is lost and thus it (seemingly) changes position, it is seen as moving. In addition, there is a Gestalt factor at play: each individual spoke only moves one single tiny step per rotation of the sectors, but each one does so at a different time. Since all spokes are grouped together, the entire spoke wheel is perceived as undergoing a continuous rotation.
Perception of MovementContrast gives the impression of stop/start movement!
Perception of Movement Spiral Illusion
Stare into the middle of the spiral After a minute, then look at a still object What happens? How can sensory adaptation explain this? This is often explained in terms of “fatigue” of
the class of neurons encoding one motion direction. It is probably more accurate to interpret this in terms of adaptation
Perceptual Organization Perceptual
Constancy Our tendency to
perceive objects as stable and unchanging despite changing sensory information
Ames Room Illusion explained
Size constancy Turnbull’s Research Is it learned?
Shape constancy Lightness constancy Color constancy
Perceptual Interpretation Sensory Deprivation and Critical Periods
Without environmental stimulation certain feature detectors may never develop
Hirsch and Spinelli’s (1970) experiment with kittens Perceptual Adaptation
Our ability to adjust to distorted perceptual circumstances Drunk goggles?
Perceptual Set Mental predisposition to perceive one thing over another Can be influences by motivation, schemas, emotions, and
experience
Perceptual Interpretation
Visual Illusions Occur because of
misleading cues in the stimulus
Gives rise to false perceptions
Individual Differences and Culture in Perception
Motivation Our desires or
needs shape our current perceptions
We perceive what we are rewarded for!
Context Values Expectations Cognitive Style Experience and
Culture Personality
Motivation in perception: When rewarded to see sea animals, people perceived a seal; when rewarded for horses, they perceived a horse.
Midget or giant? Context shapes perception.
Extrasensory Perception Refers to extraordinary
perception such as Clairvoyance – awareness
of an unknown object or event not available to the senses
Telepathy – knowledge of someone else’s thoughts or feelings
Precognition – foreknowledge of future events
Psychokinesis – “Mind over matter”
Research has been unable to conclusively demonstrate the existence of ESP or psychokinesis
Video Links Sensation and Perception – Zimbardo’s
Discovering Psychology (27:43) Sensation and Perception 1 (13:52) and 2
(13:43) from Psychology: The Human Experience
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