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Sensation and Perception. Chapter 3. Sensation vs. Perception. Sensation The experience of sensory stimulation Perception The process of creating meaningful patterns from raw sensory information . The Nature of Sensation. The Basic Process. Receptor cells

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sensation vs perception
Sensation vs. Perception
  • Sensation
    • The experience of sensory stimulation
  • Perception
    • The process of creating meaningful patterns from raw sensory information
the basic process
The Basic Process
  • Receptor cells
    • Specialized cells that respond to a particular type of energy
  • Doctrine of specific nerve energies
    • 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
sensory thresholds
Sensory Thresholds
  • Absolute threshold
    • The minimum amount of energy that can be detected 50% of the time
absolute thresholds
Absolute Thresholds
  • 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 thresholds1
Sensory Thresholds
  • Sensory adaptation
    • An adjustment of the senses to the level of stimulation they are receiving
  • Difference threshold
    • The smallest change in stimulation that can be detected 50% of the time
    • Also called the just noticeable difference
sensory thresholds2
Sensory Thresholds
  • Weber’s Law
    • States that the difference threshold is a constant proportion of the specific stimulus
    • Senses vary in their sensitivity to changes in stimulation
subliminal perception
Subliminal Perception
  • The notion that we may respond to 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 effect of subliminal information
extrasensory perception
Extrasensory Perception
  • Refers to extraordinary perception such as
    • Clairvoyance – awareness of an unknown object or event
    • Telepathy – knowledge of someone else’s thoughts or feelings
    • Precognition – foreknowledge of future events
  • Research has been unable to conclusively demonstrate the existence of ESP
the visual system
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
the visual system1
The Visual System
  • Lens
    • Focuses light onto the retina
  • Retina
    • Lining of the eye containing receptor cells that are sensitive to light
  • Fovea
    • Center of the visual field
receptor cells
Receptor Cells
  • Cells in the retina that are sensitive to light
  • Visual receptors are called rods and cones
receptor cells1

About 120 million rods

Respond to light and dark

Very sensitive to light

Provide our night vision


About 8 million cones

Respond to color as well as light and dark

Work best in bright light

Found mainly in the fovea

Receptor Cells
receptor cells2
Receptor Cells
  • Bipolar cells
    • Receive input from receptor cells
  • Ganglion cells
    • Receive input from bipolar cells
  • Blind spot
    • Area where axons of ganglion cells leave the eye
  • Dark adaptation
    • Increased sensitivity of rods and cones in darkness
  • Light adaptation
    • Decreased sensitivity of rods and cones in bright light
  • Afterimage
    • Sense experience that occurs after a visual stimulus has been removed
from eye to brain
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
color vision
Color Vision
  • Properties of color
    • Hue – refers to colors such as red and green
    • Saturation – refers to the vividness of a hue
    • Brightness – the nearness of a color to white
theories of color vision
Theories of Color Vision
  • Additive color mixing
    • Mixing of lights of different hues
    • Lights, T.V., computer monitors (RGB)
  • Subtractive color mixing
    • Mixing pigments, e.g., paints
theories of color vision1
Theories of Color Vision
  • Trichromatic theory
    • Three different types of cones
      • Red
      • Green
      • Blue-violet
    • Experience of color is the result of mixing of the signals from these receptors
    • Can account for some types of colorblindness
forms of colorblindness
Forms of Colorblindness
  • Approximately 10% of men and 1% of women have some form of colorblindness
  • Dichromats
    • People who are blind to either red-green or blue-yellow
  • Monochromats
    • People who see no color at all, only shades of light and dark
theories of color vision2
Theories of Color Vision
  • Trichromatic theory cannot explain all aspects of color vision
    • People with normal vision cannot see “reddish-green” or “yellowish-blue”
    • Color afterimages
theories of color vision3
Theories of Color Vision
  • Opponent-process theory
    • 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
color vision in other species
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
  • 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
    • Quality of texture of sound
the ear
The Ear
  • Eardrum
  • Middle ear
    • Contains three small bones; the hammer, anvil, and stirrup
    • These bones relay and amplify the incoming sound waves
the ear1
The Ear
  • Oval window
    • Membrane between middle ear and inner ear
  • Cochlea
    • Part of inner ear containing fluid that vibrates
    • This causes the basilar membrane to vibrate
the ear2
The Ear
  • Basilar membrane
    • Membrane in the cochlea which contains receptor cells, called hair cells
  • Auditory nerve
    • Connection from ear to brain
    • Provides information to both sides of brain
theories of hearing
Theories of Hearing
  • Place theory
    • 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
    • Pattern of sequential firing determines pitch
hearing disorders
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
  • Detecting common odors
    • Odorant binding protein 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
  • 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
  • Four basic tastes
    • Sweet
    • Salty
    • Sour
    • Bitter
  • Recent discovery of fifth taste
    • Umami
  • Receptor cells are located in taste buds
  • Taste buds are located in papillae on the tongue
  • Chemicals dissolve in saliva and activate receptors
kinesthetic senses
Kinesthetic Senses
  • Kinesthetic senses provide information about speed and direction of movement
    • Stretch receptors sense muscle stretch and contraction
    • Golgi tendon organs sense movement of tendons
vestibular senses
Vestibular Senses
  • Vestibular senses provide information about equilibrium and body position
  • Fluid moves in two vestibular sacs
  • Vestibular organs are also responsible for motion sickness
  • Motion sickness may be caused by discrepancies between visual information and vestibular sensation
the skin 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
  • 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
  • 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
    • Self-hypnosis
    • Accupuncture
perceptual organization
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 organization1
Perceptual Organization
  • Other principles of organization
    • Proximity
    • Similarity
    • Closure
    • Continuity
perceptual organization2
Perceptual Organization
  • Perceptual Constancy
    • Our tendency to perceive objects as stable and unchanging despite changing sensory information
  • Size constancy
  • Shape constancy
  • Brightness constancy
  • Color constancy
perception of distance and depth
Perception of Distance and Depth
  • Monocular cues – those that require only one eye
    • Aerial perspective
    • Texture gradient
    • Linear perspective
    • Motion parallax
    • Superposition
perception of distance and depth1
Perception of Distance and Depth
  • Binocular cues – those that require both eyes
    • Retinal disparity
    • Convergence
localizing sounds
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
    • This helps determine direction of the sound
perception of movement
Perception of Movement
  • Apparent movement
    • Illusion that still objects are moving
  • Autokinetic illusion
    • Perceived motion of a single object
  • Stroboscopic motion
    • Created by a rapid series of still pictures
  • Phi phenomenon
    • Apparent motion created by lights flashing in sequence
visual illusions
Visual Illusions
  • Occur because of misleading cues in the stimulus
  • Gives rise to false perceptions
individual differences and culture in perception
Individual Differences and Culture in Perception
  • Motivation
    • Our desires or needs shape our current perceptions
  • Values
  • Expectations
  • Cognitive Style
  • Experience and Culture
  • Personality