Chapter 4: Sensation and Perception


Vocabulary:

Sensation- process of receiving, converting, and transmitting raw sensory information
from the external and internal environments to the brain

Perception- process of selecting, organizing, and interpreting sensory information

Synesthesia- a mixing of sensory experiences (e.g., “seeing” colors when a sound is
heard)

Transduction- converting a stimulus to a receptor into neural impulses

Sensory reduction- filtering and analyzing incoming sensations before sending a neural
message to the cortex

Cocktail Party Phenomenon- despite distractions, you can still attend to important information.

Coding- process that converts a particular sensory input into a specific sensation

Psychophysics- study of the relation between attributes of the physical world and our
psychological experience of them

Absolute threshold- smallest amount of a stimulus needed to detect that the stimulus is
present

Difference threshold- minimal difference needed to notice a stimulus change; also called
the “just noticeable difference” (JND)

Weber’s Law- the greater the intensity of the stimulus, the greater the change needed to produce a noticeable change.

Sensory adaptation- repeated or constant stimulation decreases the number of sensory
messages sent to the brain, which causes decreased sensation

Gate-control theory of pain- theory that pain sensations are processed and altered by
mechanisms within the spinal cord

Wavelength- distance between the crests (or peaks) of light or sound waves; the shorter
the wavelength, the higher the frequency

Frequency- how often a light or sound wave cycles (i.e., the number of complete
wavelengths that pass a point in a given time)

Amplitude- height of a light or sound wave- pertaining to light, it refers to brightness; for
sound, it refers to loudness

Cornea- protective, transparent tissue that helps focus incoming light rays.

Iris- provides the color (usually brown or blue) of the eye.

Pupil- dilates or constricts in response to light intensity or emotion.

Lens- adds to the focusing begun by the cornea.

Accommodation- automatic adjustment of the eye, which occurs when muscles change
the shape of the lens so that it focuses light on the retina from objects at different
distances

Nearsightedness (myopia)- visual acuity problem resulting from cornea and lens
focusing an image in front of the retina

Farsightedness (hyperopia)- visual acuity problem resulting from the cornea and lens
focusing an image behind the retina

Retina- light-sensitive inner surface of the back of the eye, which contains the receptor
cells for vision (rods and cones)

Rods- receptor cells in the retina the detect shades of gray and are responsible for
peripheral vision and are most sensitive in dim light

Cones- receptor cells, concentrated near the center of the retina, responsible for color
vision and fine detail; most sensitive in brightly lit conditions

Fovea- a tiny pit in the center of the retina filled with cones and responsible for sharp
vision

Blind spot- where blood vessels and nerve pathways enter and exit the eyeball.

Dark adaption: during the changeover, there is a second or two before the rods are functional enough for you to see; they continue to adjust for 20-30 minutes until maximum sensitivity is reached.

Light adaption: the visual adjustment that takes place when you leave a dark area and move into sunlight.

Audition- sense of hearing

Timbre- the complex mix of frequencies and amplitudes that allows us to distinguish between the origin of sound (trumpet or violin) and the many human voices that we hear.

Pinna- the external, visible part of the ear that we envision when we think of an ear.

Auditory canal- a tube-like structure that focuses the sound.

Eardrum (tympanic membrane)- a thin, tautly stretched membrane that vibrates when hit by sound waves.

Hair cells- hearing receptors that bend from side to side.

Cochlea- three-chambered, snail-shaped structure in the inner ear containing the
receptors for hearing

Place theory- explains how we hear higher-pitched sounds; different high-pitched sounds bend the basilar membrane hair cells at different locations in the cochlea

Frequency theory- explains how we hear lower- pitched sounds; hair cells in the basilar membrane bend and fire neural messages (action potentials) at the same rate as the sound frequency.

Conduction deafness- middle- ear deafness resulting from problems with transferring sound waves to the inner ear.

Nerve deafness- inner- ear deafness resulting from damage to the cochlea, hair cells, and auditory nerve.

Olfaction- sense of smell.

Olfactory bulb- a brain structure just below the frontal lobe.

Pheromones- airborne chemicals that affect behavior, including recognition of family members, aggression, territorial marking, and sexual mating.

Lock-and-Key Theory- humans can smell various odors because each three-dimensional odor molecule fits into only one type of receptor.

Gustation- sense of taste

Five major taste sensations: sweet, sour, salty, bitter, and umami.

Umami- delicious or savory.

Glutamate- taste of protein.

Body senses- tell the brain how the body is oriented and where and how the body is moving.

Vestibular sense- sense of body orientation and position with respect to gravity and three- dimensional space.

Semicircular canal- provide the brain with balance information, particularly about the rotation of the head.

Vestibular sacs- located at the end of the semicircular canals; contain hair cells, which are sensitive to the specific angle of the head-- straight up and down or tilted.

Kinesthesia- sensory system for body posture and orientation.

Signal-Detection Theory- the detection of a stimulus involves some decision-making process as well as a sensory process. Both sensory and decision-making processes are influenced by more factors than just intensity.

Selection- choosing where to direct our attention.

Selective attention- filtering out and attending only to important sensory messages.

Feature detectors- specialized neurons that respond only to certain sensory information.

Prosopagnosia- the ability to recognize that something is a face, but cannot distinguish if it is their own or another person’s.

Habituation- tendency of the brain to ignore environmental factors that remain constant.

Gestalt (“whole” or “pattern”) psychologists were among the first to study how the brain organizes sensory impressions.

Law of Organization: tendency to distinguish between figure and ground.

Irreversible figure: the discrepancy between figure and ground becomes vague, so we have difficulty perceiving which is which.

Perceptual constancy: tendency for the environment to be perceived as remaining the same even with changes in sensory input.

Size constancy- the perceived size of an object remains the same even though the size of its retinal image changes.

Shape constancy- the brain remembers past experiences with objects that only seemed to change shape as you moved but actually remained constant.

Color constancy and brightness constancy- enable us to perceive things as retaining the same color or brightness levels even though the amount of light may vary.

Depth perception- the ability to perceive three-dimensional space and to accurately judge distance.

Binocular cues- visual input from two eyes that allows perception of depth or distance.

Retinal disparity- binocular cue to distance where the separation of the eye causes different images to fall on each retina.

Stereoscopic vision- provides important cues to depth in which the brain fuses the different images received by the two eyes into one overall visual image. Effective for up to 100m.

Convergence- binocular depth cue in which the closer the object, the more the eyes converge, or turn inward.

Monocular cues- visual input from a single eye that contributes to perception of depth or distance. Used beyond 100m.

Linear Perspective- the vanishing point on the horizon; makes things appear three-dimensional.

Interposition- objects overlap and the one that is covered appears to be in the back.

Relative Size- small objects are understood to be farther away.

Texture Gradient- with increased distance, things appear smaller and denser.

Aerial Perspective- things far away have less detail. Around the edges, there is “blue atmosphere.”

Light and Shadow- bright things are understood to be close and dark things far away.

Motion Parallax (relative motion)- when an observer is moving, close objects appear to whiz by, far ones move slowly, and very distant ones remain stationary.

Accommodation- refers to changes in the shape of the lens of the eye in response to stimuli.

Trichromatic theory- theory that color perception results from mixing three distinct color systems-- red, green, and blue.

Opponent-process theory- theory that color perception is based on three systems of color opposites-- blue-yellow, red-green, and black-white.

Perceptual adaptation- the ability to adapt to our perceptions by re-training our brains to create a newly coherent and familiar world.

Perceptual set (or expectancies)- readiness to perceive in a particular manner based on experiences.

Frame of reference- perceptions of people, objects, or situations are affected by their frame of reference, or context.

Bottom- Up processing- information processing that begins “at the bottom” with raw sensory data that feed “up” to the brain.

Top- Down processing- information processing that starts “at the top” with the observer’s thoughts, expectations, and knowledge, and works “down.”


Chapter Outline:

  • Sensation: the passive process of receiving, converting, and transmitting raw sensory information from external and internal environments to the brain.
  • Perception: the process of selecting, organizing, and interpreting sensory information.
  • Sensation occurs in your sense organs; perception takes place in your brain.
  • Information→Sensation→Perception= I Sense People

Understanding Sensation
  • Synesthesia: a mixing of sensory experiences (e.g., “seeing” colors when a sound is heard).
    • Example 1: Someone with synesthesia may see streaks of purple every time she hears her name.
    • Example 2: Someone with synesthesia may see streaks or bursts of orange when eating ice cream.
Processing: Getting the Outside Inside
  • Receptors receive and process sensory information from the environment.
    • They respond to a distinct stimulus, such as light, sound waves, or chemical molecules.
  • Transduction: receptors convert the stimulus into neural impulses, which are then sent to the brain; a physical process.
    • Example: Receptors in the inner ear convert sound waves to electrochemical signals.
  • Some level of filtering is needed so that the brain is not overwhelmed with unnecessary information.
    • The brain needs to respond to stimuli that are important to our survival.
  • Sensory reduction: filters and analyzes incoming sensations before sending a neural message to the cortex of the brain.
  • RAS (Reticular Activating System)
    • Cells in the reticular formation send messages via the thalamus to alert the cortex → cells learn to screen out certain messages while allowing others to go on to higher brain centers.
    • Example: A sudden loud noise will generally wakes a person up.
  • Cocktail Party Phenomenon: Despite distractions, you can still attend to important information.
    • Example: You are rocking out to music blasting from your iHome, but you hear your mom call your name to come downstairs for dinner.
  • Coding: a process that converts sounds and smells as distinct sensations.
  • Deals with the rate of neuron firing and which ones fire.
  • Respective neural impulses travel by different routes and arrive at different parts of the brain.

Thresholds: Testing Our Sensitivity
  • Psychophysics: study of the relation between attributes of the physical world (e.g., sound and smell) and our psychological experience of them.
  • Absolute threshold: the smallest amount of a stimulus needed to detect that the stimulus is present.
  • Difference threshold: the minimal difference needed to notice a stimulus change; also called the “just noticeable difference” (JND).
  • Note: Everyone’s thresholds are slightly different.
  • Determine the loss or gain of noticing a stimulus by comparison.
  • Weber’s Law: the greater the intensity of the stimulus, the greater the change needed to produce a noticeable change.
    • Example: You have a ten-pound backpack. It feels heavier when you add your psychology text book. Your friend has a fifty-pound backpack. It feels the same when she adds her book.
  • Sensory thresholds exist not only for hearing but also for vision, taste, smell, and skin senses.
  • Vestibular vs. Kinesthesia
    • The vestibular sense is the sense of body orientation and position with respect to gravity and three-dimensional space.
    • Kinesthesia is the sense that provides the brain with information about body posture and orientation, as well as body movement.

Adaptation: Weakening Our Sensitivity
  • Sensory adaption: repeated or constant stimulation decreases the number of sensory messages sent to the brain, which causes decreased sensation.
    • Allows our brains time and space for paying attention to change.
    • Limitations aid survival.
  • Receptors higher up in the sensory system get “tired” and actually fire less frequently.
  • “Turning down the volume” in repetitive information helps the brain cope with an overwhelming amount of sensory stimuli.
  • Endorphins are neurotransmitters that relieve pain by inhibiting pain perception (like morphine).
  • Gate- control theory: theory that pain sensations are processed and altered by mechanisms within the spinal cord.
    • Robert Melzack and Patrick Wall
    • A gatekeeper in the spinal cord either blocks pain signals or allows them to pass on to the brain.
    • Large fibers carry competing pressure messages that help block some of the pain.
    • Messages from the brain itself can also control the pain gate.
    • Other research:
      • Substance P opens the pain gate and endorphins close it.
      • The brain is capable of generating pain and other sensations on it’s own.
    • Gate-Control Theory: Pain Sensations Altered By Spinal Cord=Grilled Chicken Tastes Pretty Salty After Being Sauced Carelessly

How We See and Hear
Vision: The Eyes Have It
-Waves of Light-
  • Vision is based upon the wave phenomena.
  • Wavelength: the distance between the crests (or peaks) of light or sound waves.
    • Determines the hue (color) we see.
  • Frequency: how often a light or sound wave cycles (i.e., the number of complete wavelengths that pass a point in a given time.)
    • Also determines the hue (color).
  • Larger wavelength means smaller frequency and vice versa.
  • Amplitude: the height of a light or sound wave--pertaining to light, it refers to brightness; for sound, it refers to loudness.
  • Vision is based on light waves waves of electromagnetic energy of a certain wavelength.
  • Most wavelengths are invisible to the human eye.
    • The visible spectrum is detected by our receptors.
-Eye Anatomy and Function-
  • Eyes are designed to capture light and focus it on receptors at the back of the eyeball.
  • Receptors convert light energy into neural signals to be interpreted by the brain.
  • Path of light: Cornea Iris Pupil Lens Retina= Corn Is Popped Like (pop) Rocks

-Cornea, Iris, Pupil, and Lens-
  • Cornea : protective, transparent tissue that helps focus incoming light rays.
    • Has a convex (outward) curvature.
  • Iris : provides the color (usually brown or blue) of the eye.
  • Pupil : dilates or constricts in response to light intensity or emotion.
    • Muscles allow the pupil to dilate.
  • Lens : adds to the focusing begun by the cornea.
    • Adjustablesmall muscles change its shape to allow us to focus on objects close to the eye or farther away.external image wMSQt72nmGPG8x1GAY2p16dOlkLXtBr37qNL3xdLFAvt3FbEnl8-BQr8P3TB4b4I_jKsnI8niK-4Fmv_2kok_UwKFp6inLYRxhTlBt-j3f-Gnl1XFnE
  • Accommodation : the automatic adjustment of the eye (by thickening or curving), which occurs when muscles change the shape of the lens so that it focuses light on the retina from objects at different distances.
  • The lens focuses the image of any object-- near or far-- on the retina at the back of your eye.
  • Nearsightedness (Myopia): a visual acuity problem resulting from the cornea and lens focusing an image in front of the retina.
    • Light rays are focused at a point in front of the retina and, as a result, the image is blurred.
    • You cannot see far away.
  • Farsightedness (Hyperopia): a visual acuity problem resulting from the cornea and lens focusing an image behind the retina.
    • The eyeball is shorter that normal, and the light is focused at a point beyond the retina.
    • You cannot see up close.
  • Lenses start to lose elasticity and the ability to accommodate for near vision.
    • Presbyopia
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-Retina-
  • Retina: the light- sensitive inner surface of the back of the eye, which contains the receptor cells for vision (rods and cones)
    • Contains blood vessels and a network of neurons that transmit neural information to the occipital lobes of the brain.
  • Rods: receptor cells in the retina that detect shades of gray, are responsible for peripheral vision, and are most sensitive in dim light.
    • 120 million rods
    • More sensitive to light.
    • Enables us to see in dim light.
  • Cones: receptor cells; concentrated near the center of the retina; responsible for color vision and fine detail; most sensitive in brightly lit conditions.
    • Gives ability to see things in fine detail
    • Maximally sensitive to red, green or blue.
    • Sensitive to many wavelengths.
  • Fovea: a tiny pit in the center of the retina filled with cones and responsible for sharp vision.
  • Blind spot: Where blood vessels and nerve pathways enter and exit the eyeball.
    • The brain fills in the information missing from the blind spot with the information from adjacent areas on the retina or with images from the other eye.
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  • When brightness level suddenly changes, you are momentarily blinded because the rods are bleached and, therefore, nonfunctional.
  • Dark adaption: During the changeover, there is a second or two before the rods are functional enough for you to see; they continue to adjust for 20-30 minutes until maximum sensitivity is reached.
  • Light adaption: the visual adjustment that takes place when you leave a dark area and move into sunlight.
    • Cones adjust for 7-10 minutes until maximum sensitivity is reached.
  • As a person ages, the adaption takes longer.

Hearing: A Sound Sensation
  • Audition: sense of hearing.
- Waves of Sound-
  • Sound is based on pressure waves in the air.
  • Pressure variations can result from an impact or vibrations.
  • Sound waves have characteristics of wavelength (or frequency), amplitude (height), and complexity (mixture; rich vs. pure).
    • The frequency determines the pitch of sound that is heard.
    • The amplitude determines the loudness that is heard.
    • Complexity determines timbre.
      • Timbre: the complex mix of frequencies and amplitudes that allows us to distinguish between the origin of sound (trumpet or violin) and the many human voices that we hear.
-Ear Anatomy and Function-
  • The outer ear gathers and delivers sound waves to the middle ear.
  • The middle ear amplifies and concentrates the sounds.
  • The inner ear contains receptor cells that transform the mechanical energy created by sounds into neural impulses.
  • Sound waves are gathered and funneled into the outer ear by the pinna.
    • Pinna: the external, visible part of the ear that we envision when we think of an ear.
  • The pinna channels sound waves to the auditory canal
    • Auditory canal: a tube-like structure that focuses the sound.
  • Eardrum (tympanic membrane): a thin, tautly stretched membrane that vibrates when hit by sound waves.
  • The vibrating eardrum causes the malleus (hammer), the incus (anvil), and the stapes (stirrup) to vibrate.
    • Together they are called the ossicles.
    • Malleus Incus Stapes =Make Iced Snowcones
  • The stapes bone presses on the oval window causing it to vibrate.
  • Vibrations of the oval window create waves in the fluid that fills the cochlea.
    • Cochlea: a three- chambered, snail- shaped structure in the inner ear containing the receptors for hearing.
      • Also contains the basilar membrane.
  • Hair cells: hearing receptors that bend from side to side.
  • When the hair cells bend, the mechanical energy of the sound wave is trans-duced into electrochemical impulses that are carried by the auditory nerve to the brain.

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  • Place theory: explains how we hear higher-pitched sounds; different high- pitched sounds bend the basilar membrane hair cells at different locations in the cochlea.
    • We hear higher pitches because the sound wave causes the eardrum, ossicles, and oval window to vibrate.
    • The vibrations produce a “traveling wave” through the fluid of the cochlea which bends the hair cells all along the basilar membrane.
    • Part 1: Eardrum, Ossicles, Oval Window, Vibration=Every Ostrich Only Wants Visitors
    • Part 2: Wave To Cochlea Bends Hair Cells Along Basilar Membrane= When Tiny Children Bake Hot Cookies All Becomes Madness
  • Frequency theory: explains how we hear lower- pitched sounds; hair cells in the basilar membrane bend and fire neural messages (action potentials) at the same rate as the sound frequency.
  • Some sounds are louder than others because it they depend on the intensity of the sound waves.
  • Conduction deafness: middle- ear deafness resulting from problems with transferring sound waves to the inner ear.
  • Nerve deafness: inner- ear deafness resulting from damage to the cochlea, hair cells, and auditory nerve.
    • Disease and biological changes associated with aging can cause nerve deafness.
    • The most common and preventable cause is continuous exposure to loud noise, which can damage hair cells and lead to permanent hearing loss.
  • Damage to the nerve or receptor cells is almost always irreversible.
    • Would need a cochlear implant.
      • Auditory nerve must be intact so that the implant can bypass the hair cells and directly stimulate the nerve.
      • Implant produces only a crude approximation of hearing.
Our Other Senses
Smell and Taste: Sensing Chemicals
-Olfaction-
  • Olfaction : sense of smell.
  • Humans can detect over 10,000 distinct smells.
  • Sense of smell results from stimulation of receptor cells in the nose.
  • The receptors are embedded in a mucus-coated membrane called the olfactory epithelium.
    • Receptors are actually modified neurons with branched dendrites extending out into the epithelium.
  • Chemical molecules in the air pass through the nose and come in contact with the dendrites, initiating a neural impulse
  • Impulse travels along the neuron’s axon directly to the olfactory bulb.
    • Olfactory bulb : a brain structure just below the frontal lobe.
      • Most information is processed here before being sent to other areas of the brain.
  • Each odorous chemical excites a portion of the olfactory bulb, and they are coded and detected according the the stimulated area.
  • Pheromones : airborne chemicals that affect behavior, including recognition of family members, aggression, territorial marking, and sexual mating.
  • Lock-and-Key Theory : Humans can smell various odors because each three-dimensional odor molecule fits into only one type of receptor.

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- Gustation-
  • Gustation: sense of taste.
    • Least critical of the senses.
  • The major function is to provide information about substances that are entering our digestive tracts so that we can screen out those that may be harmful.
    • Aided by other senses: smell, temperature, touch.
  • Five major taste sensations: sweet, sour, salty, bitter, and umami.
    • Umami: delicious or savory.
      • Separate taste and receptor that is sensitive to glutamate.
        • Glutamate: taste of protein.
          • Found in meats, meat broths, and MSG.
          • Major contributor to the tastes of natural foods.
  • Taste receptors respond differently to the varying food and liquid molecules.
    • Taste buds (receptors) are clustered on our tongues within little bumps called papillae.
  • A small number of taste receptors are also found in the palate and the back of our mouths.
  • Children, who have abundant taste buds, often dislike foods with strong or unusual tastes because their taste buds are replaced every 7 days.
  • Many food and taste preferences result from childhood experiences and cultural influences.
  • Pickiness relates to the fact that the sense of taste normally enables humans and non-humans to differentiate between foods that are safe to eat and foods that are poisonous.

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The Body Senses: More Than Just Touch
  • Body senses: tell the brain how the body is oriented and where and how the body is moving.
    • Senses include the skin senses, the vestibular sense, and kinesthesia.
- The Skin Senses-
  • Skin not only protects the internal organs, but also provides the brain with basic survival information.
  • The “mapping” of the skin shows there are three basic skin sensations: touch (or pressure), temperature, and pain.
  • Receptors for these sensations occur in various concentrations and depths in the skin.
  • Researchers have found that the average square centimeter of skin contains about 6 cold spots where only cold is sensed, and one or two warm spots where only warmth can be felt.
    • There are no separate “hot” receptors.
    • Cold receptors detect coolness and extreme temperatures--both hot and cold.
- The Vestibular Sense-
  • Vestibular sense: sense of body orientation and position with respect to gravity and three- dimensional space.
    • Sense of balance.
  • The vestibular apparatus is located in the inner ear and is composed of the vestibular sacs and the semicircular canals.
    • Semicircular canals: provide the brain with balance information, particularly about the rotation of the head.
    • Vestibular sacs: located at the end of the semicircular canals; contain hair cells, which are sensitive to the specific angle of the head-- straight up and down or tilted.
  • Liquid in the canals moves and bends hair cell receptors.
  • Information from the semicircular canals and the vestibular sacs is converted to neural impulses which are then carried to the appropriate section of the brain.
  • Information from the vestibular sense is used by the eye muscles to maintain visual fixation and, sometimes, by the body to change body orientation.
  • If the vestibular sense gets overloaded or becomes confused, the result is often dizziness and nausea.
  • Random movements are more likely to produce motion sickness.
-Kinesthesia-
  • Kinesthesia: sensory system for body posture and orientation.
  • Kinesthetic receptors are found throughout the muscles, joints, and tendons of the body.
  • As we move, our kinesthetic receptors respond by sending messages to the brain.

Understanding Perception
  • Illusion: false or misleading perceptions.
  • Sometimes, they occur because of actual physical distortions.
    • Example: mirages.
  • Perception is influenced by motivation.
  • The problem? Motivation affects perception.
    • Example: You are desperately looking for your lost car keys because you really don’t want to be late for your first day at work, and you fail to notice them hanging on the hook right in front of you.
  • The solution? Signal-Detection Theory: the detection of a stimulus involves some decision-making process as well as a sensory process. Both sensory and decision-making processes are influenced by more factors than just intensity.

Selection: Extracting Important Messages
  • The first step of perception is selection.
    • Selection: choosing where to direct our attention.
    • Example: You walk by a classroom with its door open. Unlike the students in that class, you are not particularly concerned with the teacher’s lesson. You are more focused on spotting your friends and waving to them.
  • There are three major factors involved in the act of paying attention to stimuli in our environment: selective attention, feature detectors, and habituation.
- Selective Attention-
  • Selective attention: filtering out and attending only to important sensory messages.
- Feature Detectors-
  • Feature detectors: specialized neurons that respond only to certain sensory information.
    • This is the second major feature in selection.
  • Feature detectors are found in the temporal and occipital lobes that respond maximally to faces.
    • Damage to those ares can produce prosopagnosia.
      • Prosopagnosia: the ability to recognize that something is a face, but cannot distinguish if it is their own or another person’s.
- Habituation-
  • Habituation : tendency of the brain to ignore environmental factors that remain constant.
    • We quickly habituate (respond less) to predictable and unchanging stimuli.
  • We automatically select stimuli that are intense, novel, contrasting, moving, and repetitious.

Organization: Form, Constancy, Depth, and Color
  • Raw sensory data is organized in terms of form, constancy, depth, and color.
- Form Perception-
  • Gestalt (“whole” or “pattern”) psychologists were among the first to study how the brain organizes sensory impressions.
    • Emphasized the importance of organization and patterning in enabling us to perceive the whole stimulus.
    • Proposed laws of organization that specify how people perceive form.
      • Note: these “laws” are not true across cultures and should therefore be treated as heuristics.
    • Law of Organization: tendency to distinguish between figure and ground.
      • Example: The brain is organizing sensations of black lines and white paper into words and letters that are perceived against a backdrop of white pages.
      • Letters constitute the figure; pages constitute the ground.
  • Irreversible figure: the discrepancy between figure and ground becomes vague, so we have difficulty perceiving which is which.
- Perceptual Constancies-
  • Perceptual constancy: tendency for the environment to be perceived as remaining the same even with changes in sensory input.
    • Without perceptual constancy, things would seem to grow as we got closer to them, change shape as our viewing angle changed, and change color as light levels changed.
  • Most perceptual constancies are based on prior experience and learning.
  • Size constancy: the perceived size of an object remains the same even though the size of its retinal image changes.
    • Colin Turnbull (1961): showed an African native (who had lived in a dense forest and had only seen at a distance of 100 yards his entire life) a group of water buffalo from a distance and he thought that they were insects. They got closer to the buffalo, and the native thought it was witchcraft.
  • Shape constancy: The brain remembers past experiences with objects that only seemed to change shape as you moved but actually remained constant.
    • Adelbert Ames: created the Ames room where the observer believes the entire room is rectangular but it is actually a trapezoid. The room creates an illusion so that on one side, the person looks like a giant and on the other, a midget. Our brains try to apply the standard perceptual processes of shape and size constancy to an unusual situation.
  • Color constancy and brightness constancy enable us to perceive things as retaining the same color or brightness levels even though the amount of light may vary.
  • Color constancy and brightness constancy are learned from experience with familiar objects.
  • Perceptual, Size, Shape, Color, Brightness= People See Some Cave Bats

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- Depth Perception-
  • Depth perception: the ability to perceive three-dimensional space and to accurately judge distance.
  • When you add the ability to accurately perceive distance to the ability to judge the height and width of an object, you are able to perceive the world in three dimensions.
  • Nature vs. Nurture
    • Nature: Using a visual cliff, a tabletop is made with a shallow side and side that has clear glass. Under the clear glass is a pattern that is similar to that of the shallow side. The clear glass simulates a steep cliff. A baby is coaxed from the shallow side to the glass side. It was found that the baby hesitates to come to the glass side.
    • Nurture: Babies at 2 months show that their heart rate increases when placed on the glass side rather than on the shallow side.
  • Binocular cues: visual input from two eyes that allows perception of depth or distance.
    • Retinal disparity: binocular cue to distance where the separation of the eye causes different images to fall on each retina.
    • Stereoscopic vision: provides important cues to depth in which the brain fuses the different images received by the two eyes into one overall visual image. Effective for up to 100m.
    • Convergence: binocular depth cue in which the closer the object, the more the eyes converge, or turn inward.
    • Allen Souchek (1986): found that depth perception is better when looking directly at an object, rather than out of the corner of your eye.
  • Monocular cues: visual input from a single eye that contributes to perception of depth or distance. Used beyond 100m.
    • Retinal disparity and convergence are inadequate in judging distances longer than the length of a football field.
    • 7 cues:
      • Linear Perspective: the vanishing point on the horizon; makes things appear three-dimensional.
      • Interposition: objects overlap and the one that is covered appears to be in the back.
      • Relative Size: small objects are understood to be farther away.
      • Texture Gradient: with increased distance, things appear smaller and denser.
        • Example: From far away, it is difficult to distinguish individual stalks of wheat. The whole field looks like one texture.
      • Aerial Perspective: things far away have less detail. Around the edges, there is “blue atmosphere.”
      • Light and Shadow: bright things are understood to be close and dark things far away.
      • Motion Parallax (relative motion): when an observer is moving, close objects appear to whiz by, far ones move slowly, and very distant ones remain stationary.
        • Example: You’re staring out your car window while driving at 60mph. The electricity poles fly by, but the mountains never seem to move.
    • Accommodation: refers to changes in the shape of the lens of the eye in response to stimuli.
-Color Perception-
  • We can detect 7 million different hues.
  • Two theories of color perception: trichromatic theory and opponent-process theory.
  • Trichromatic theory: theory that color perception results from mixing three distinct color systems-- red, green, and blue.
    • First proposed by Thomas Young in the early 19th century and refined by Hermann von Helmholtz and others.
    • Proponents of this theory demonstrated that activation of different combinations of these three colors could yield the full spectrum of colors we perceive.
    • Two major flaws:
      • Does not explain defects in color vision.
      • Does not explain color aftereffects.
  • Opponent-process theory: theory that color perception is based on three systems of color opposites-- blue-yellow, red-green, and black-white.
    • Proposed by Ewald Hering later in the 19th century.
    • Each color receptor responds either to blue or yellow, or to red or green, with the black-or-white system responding to differences in brightness levels.
    • If one color receptor is stimulated, its pair is inhibited.
  • Most color vision defects are weaknesses--color confusion rather than color blindness.
-Two Correct Theories-
  • Color is processed in a trichromatic fashion at the level of the retina (in the cones) and in an opponent fashion at the level of the optic nerve and the thalamus (in the brain).
- A Gender & Cultural Diversity-
  • Most Gestalt psychologists were on formally educated people from urban European cultures.
  • A.R Luria (1976): questioned whether Gestalt laws were true for all participants regardless of education level in particular.
    • Tested in the USSR (Soviet Russia).
    • Found that the Gestalt laws are only valid for those that were taught geometrical concepts.
    • Faults:
      • Relies on 2-D pictures and illustrations.
    • Experience with pictures and illustrations is needed to portray 2-D objects and 3-D ones.

Interpretation: Explaining Our Perceptions
  • This final stage of perception--interpretation--is influenced by several factors, including perceptual adaptation, perceptual set, frame of reference, and bottom-up or top-down processing.
  • Perceptual adaptation: the ability to adapt to our perceptions by re-training our brains to create a newly coherent and familiar world.
    • George Stratton (1897): wore special lenses that altered the look of his environment. After about a week, he had completely adjusted to his perceptual environment.
  • Perceptual set (or expectancies): readiness to perceive in a particular manner based on experiences.
    • We largely see what we expect to see.
  • Frame of reference: perceptions of people, objects, or situations are affected by their frame of reference, or context.
  • Bottom- Up processing: information processing that begins “at the bottom” with raw sensory data that feed “up” to the brain.
    • Takes longer but is more accurate.
    • Example: When first learning to read, we determined that a certain arrangement of lines and “squiggles” represented specific letters. Then we figured out that those were words.
  • Top- Down processing: information processing that starts “at the top” with the observer’s thoughts, expectations, and knowledge, and works “down.”
    • Faster but more prone to errors.
    • Example: We quickly perceive the words in a sentence before the individual letters.

Research Highlight
  • We are able to perceive something without conscious awareness.
    • Example: Flashing a happy face followed by a neural face. The participant’s facial muscles would match those of the unconscious facial expression.
  • Subliminal stimuli are weak but subliminal persuasion is unclear.
  • Subliminal: pertaining to any stimulus presented below the threshold of conscious awareness.
  • Extrasensory Perception (ESP): Perceptual, or “psychic” abilities that supposedly go beyond the known senses (e.g., telepathy, clairvoyance, precognition, and psychokinesis).
    • Telepathy: ability to read other people’s minds.
    • Clairvoyance: ability to perceive objects and events that you cannot predict with your normal senses.
    • Precognition: ability to predict the future.
    • Psychokinesis: ability to move objects without touching them.
  • Scientific investigations into ESP began with Joseph B. Rhine in the early 1900s.
    • Zener cards: set of 25 cards that include 5 different symbols: plus sign, square, star, circle, and wavy lines.
    • Experimenter asks the person with ESP to perform their abilities with the card.
    • Criticisms:
      • Lack of experimental control.
      • Outline of symbol was seen on the back.
      • Experimenters could give the answer away by facial expression.
      • Lack of stability and repetition.

Important People:

Ronald Melzack and Patrick Wall (1965): first proposed the gate-control theory, which suggests the experience of pain depends partly on whether the neural message gets past a “gatekeeper” in the spinal cord. Their research first began when Melzack began to work with patients who suffered from "phantom limb" pain — people who feel pain in an arm or leg that has been removed. He found that pain often has little survival value, and some pains are entirely out of proportion to the degree of tissue damage.

M.C. Escher: a Dutch painter who created examples of perceptual distortion. They are drawn so that they seem like 3-D objects, but in reality the parts don’t assemble into logical wholes; his paintings helped psychologists understand the principle of form organization.

Gestalt (meaning ‘whole or ‘pattern’) psychologists: among the first to study how the brain organizes sensory impressions. They emphasized the importance of organization in allowing humans to perceive an entire stimulus. Additionally, they proposed laws of organization that specify how people perceive form, or the Gestalt principles. The most fundamental principle is the tendency to distinguish between figure and ground. Other principles include proximity (objects physically close together are grouped together), continuity (objects that continue a pattern are grouped together), closure (tendency to see a finished unit), and similarity (similar objects are grouped together).

A.R. Luria (1976): one of the first psychologists to question whether the Gestalt principles were held true of all participants, regardless of education and cultural setting. Luria’s participants included Ichkeri women from remote villages in the USSR, collective farm activists, and female students in a teacher’s school. She presented them with an incomplete circle and only the educated students actually called it a ‘circle.’ The other participants called it by objects they resembled. Thus, Luria found that the Gestalt laws of perceptual organization are valid only for people who have been taught geometrical concepts.

Colin Turnbull (1961): an anthropologist who provided an example of an adult who had never developed a sense of size constancy. He studied the Twa people in the Congo River Valley and found particularly interesting a native named Kenge. Turnbull took Kenge on a Jeep ride, and Kenge was unable to identify water buffalo that were far away as buffalo--he mistook them to be insects only due to how far away they were.

Adelbert Ames: an ophthalmologist who demonstrated the power of shape and size constancies by creating a Ames room in which there are sloped ceiling and floors. This provided misleading depth cues.

Allen Souchek (1986): found that depth perception is better when one looks directly at an object, rather than out out of the corner of one’s eye.

R.L. Gregory (1969): stated that retinal disparity and convergence are inadequate in judging distances longer than the football field. He once said, “we are effective one-eyed for stances greater than perhaps 100 meters.”

Thomas Young: proposed the trichromatic theory in the 19th century. The theory stated that color perception results from mixing three distinct color systems--red, green, and blue. He performed numerous amounts of experiments to establish the wave theory of light: with the ripple tank he demonstrated the idea of interference in the context of water waves; with the double-slit experiment, he demonstrated interference in the context of light as a wave.

Hermann von Helmholtz: refined Thomas Young’s theory by specifically adding that: the three types of cone photoreceptors could be classified as short-preferring (blue), middle-preferring (green), and long-preferring (red), according to their response to the wavelengths of light striking the retina. He is also known as one of the founders of experimental psychology.

Ewald Hering: proposed the opponent-process theory, which says that color perception is based on three systems of color opposites--blue/yellow, red/green, and black/white. He believed that the visual system worked based on a system of color opponency.

George Wald (1964): demonstrated that they are three different types of cones in the retina, each with its own type of photopigment. Wald and his colleagues used chemical methods to extract pigments from the retina. Using aspectrophotometer, they were able to measure the light absorbance of the pigments. Since the absorbance of light by retina pigments corresponds to the wavelengths that best activate photoreceptor cells, this experiment showed the wavelengths that the eye could best detect.

R.L. DeValois (1965): while studying electrophysiological recording of cells in the optic nerve and optic pathways to the brain, he discovered cells that respond to color in an opponent fashion in the thalamus. Thus, he proved that both of the color theories are correct.

George Stratton (1897): a psychologist who answered if a person could ever adapt a distorted world. He worse special lenses for eight days. At first, he had a great deal of difficulty navigating, but by the third days, he was able to adjust. Thus, his experiment showed how we are able to adapt our perceptions by retaining our brains to create a newly coherent and familiar world.

Hubel and Weisel (1980s): these Swedish neurophysiologists performed many experiments that greatly expanded scientific knowledge of sensory processing. One of their most famous experiments was when they inserted a microelectrode into the primary visual cortex of an anesthetized cat. They then projected patterns of light and dark on a screen in front of the cat. They found that some neurons fired rapidly when presented with lines at one angle, while others responded best to another angle. They called these neurons "simple cells." Still other neurons, which they termed "complex cells," responded best to lines of a certain angle moving in one direction. These studies showed how the visual system builds an image from simple stimuli into more complex representations. They won the Nobel Prize in 1981 for their work.

Ernst Weber: a German physician who is sometimes dubbed one of the founders of experimental psychology. He did a lot of research on the sensory organs. His work upon the ear, pressure, temperature, and ‘space sense’ gave the deciding impulse to the introduction of the experimental movement into psychology.

Wilhelm Wundt: a German doctor and psychologist, among many other things, Wundt is best known as one of the founding figures of modern psychology. He conducted many studies in the what we known today as the fields of sensation and perception. Of these studies, most of them focused on vision.




Interesting Facts:

1. Absolute Pitch is the ability to identify or create a certain pitch only by memory without referencing examples of the pitch. It is often thought to be quite rare with only one out of ten thousand people possessing this ability. In the study, “Absolute memory for musical pitch: Evidence from the production of learned melodies,” the ability’s supposed rarity is challenged. Forty-six participants in the study sang two well known songs; forty percent of whom sang the correct pitch on at least one song, twelve percent sang the correct pitch on both songs, and forty-four percent came within two semitones of the correct pitch on both songs. These results put into question the actual rarity of absolute pitch (Levitin 1).

2. Nine million people across the United States suffer from colorblindness. Due to the relative prevalence of the problem, geographers such as Cynthia A. Brewer have begun to find methods to make typically color-coded maps more accessible to the colorblind. The colorblind can still see the lightness and darkness of colors even if they cannot differentiate between hues, so using different shades or tones would make the map clearer. Colors that cause confusion for people with red/green color blindness, such as green, red-orange, and yellow, can be forgone for colors that are easier to see, such as blues ("Map Makers Can Avoid Confusing the Color Blind").

3. Though taste is not a critical sense, over 200,000 people a year visit doctors for taste and smell related diseases that affect their quality of life. One of the most common disorders is phantom taste perception, or tasting something that is not really there. A reduced sense of taste is called hypogeusia and the inability to taste, whether it is caused by the patient being unable to smell or the far more uncommon actual taste loss, is called ageusia. People may be born with these disorders or they may result from poor oral hygiene, head injuries, or radiation, among other injuries or illnesses (“Taste Disorders”).

4. Most sounds can be heard using only one ear but having two ears is essential to locating the source of the sounds. A researcher named Konishi tested the the relationship two ears have to sound placement using owls as test subjects. Sound not coming from directly in front of the middle of the head but instead to one side or the other, takes microseconds longer to reach the far ear than the close ear. Konishi inserted headphones into owls’ ears (which, strangely enough, are positioned asymmetrically on their heads) and played a sound in one ear and after a few microseconds played the same sound in the other ear. By watching owls turn their heads in response to the stimulus Konishi was able to determine how the length of intervals between sound denoted location. Two-hundred microseconds’ difference of certain sound waves reaching the owls ears was enough for the bird to sense a difference in the location of the sound source. Humans also locate sound sources in this way but human hearing is not as keen and only registers time gaps above 600 microseconds for similar sounds (Goldberg).

5. A woman in Munich, Germany, suffered motion blindness after a stroke. With motion blindness she could still see objects in all their detail but she could not see objects moving. For example, a person walking around would look like someone standing stationary in on location and a few seconds later as someone standing stationary in another location with no sign movement in between those two images. In this instance the pathway responsible for motion perception, more simple in function than the visual cortex, had been damaged (Montgomery).

Extra: A website that has a sensation and perception jeopardy board that could be used for studying: http://www.uni.edu/walsh/jeopardy.html




Works Cited

Cilliers, Tamsyn. Class Notes. 3-9 Nov. 2010.

Goldberg, Jeff. "The Value of Having Two Ears." Howard Hughes Medical Institute | Biomedical
Research & Science Education (HHMI). Web. 29 Mar. 2011.
http://www.hhmi.org/senses/c220.html.

Goldstein, B. 2001. Sensation and Perception, 6th ed. London: Wadsworth.


Huffman, Karen. Psychology in Action. 8th ed. Hoboken: John Wiley & Sons, Inc., 2007.


Levitin, Daniel J. "Absolute Memory for Musical Pitch: Evidence from the Production of Learned
Melodies." Perception & Psychophysics 56 (1994): 414-23. Encyclopedia of Psychology.
Web. 27 Mar. 2011.
<http://www.psychology.org/links/Environment_Behavior_Relationships/Sensation_and_Pe
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"Map Makers Can Avoid Confusing the Color Blind." Penn State News. 25 Apr. 2000. Web. 27
Mar. 2011. http://www.psu.edu/ur/2000/colorblindness.html.

Marieb, Elaine N. Human Anatomy & Physiology. 6th ed. San Francisco: Benjamin Cummings, 2003.


Montgomery, Geoffrey. "The Strange Symptoms of Blindness to Motion." Howard Hughes Medical
Institute | Biomedical Research & Science Education (HHMI). Web. 29 Mar. 2011.
http://www.hhmi.org/senses/b210.html.

Talamo, Laura. Cracking the AP Psychology Exam. New York: Random House, 2010. Print. Princeton Review.


"Taste Disorders." National Institute on Deafness and Other Communication Disorders [NIDCD].
July 2009. Web. 27 Mar. 2011. <http://www.nidcd.nih.gov/health/smelltaste/taste.asp>.