Sensation

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Sensation Perception

• Subtitle

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Overview

• Sensory organs receive stimuli
• Messages go through process called
  transductionsignals are transformed into
  neural impulses
• Neural impulses travel 1st to thalamus, then on
  to different cortices in the brain (exception
  smell)
• What we sense and perceive influenced by many
  factors
• Sensory adaptationdecreasing responsiveness due
  to constant stimulation
• Sensory habituationperception of sensations
  partially due to how focused we are on them
• Cocktail-party phenomenonpaying close attention
  to something close, but shift attention when hear
  name across the room
• Sensationactivation of our senses
• Perceptionprocess of understanding these
  sensations

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Categories of Senses

• Energy sensesgather energy
• Visionlight waves
• Hearingsound waves
• Touchpressure
• Chemical sensesgather chemicals
• Taste Smell
• Body position balance senses
• Vestibular kinesthetic

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Energy Senses Vision

• Dominant sense in humans
• Step One gathering light
• Light is reflected off of objects and gathered by
  eye
• Light intensity determines brightness
• Light wavelength determines color perceived
• Step Two within the eye
• Reflected light enters eye thru cornea,
  protective covering that helps focus the light
• Light then goes thru pupil, which is like a
  camera shutter
• Muscles that control the pupil, called iris, open
  it (dilate) to let in more light, or make it
  smaller (constrict) to let in less light
• Thru process of accommodation, light that enters
  pupil is focused by the lens, which is curved and
  flexible in order to focus the light
• As light passes thru lens, image is flipped
  upside down and inverted, then projected on the
  retina, which is like a screen in the back of
  your eye
• On the retina are specialized neurons that are
  activated by the different wavelengths of light

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Energy Senses Vision

• Step 3 transduction
• Transduction occurs when light activates the
  neurons in the retina
• First layer of cells are cones (activated by
  color) and rods (respond to black and white)
• Rods outnumber cones 201, and are distributed
  throughout retina cones concentrated toward
  center of retina
• Center of retina is an indention, called the
  fovea, contains the highest concentration of
  cones
• Focusing on something focuses light onto the
  fovea and you see it in color peripheral vision
  relies on rods and is mostly black/white
• If enough rods cones fire, they activate next
  layer of bipolar cells if enough bipolar cells
  fire, next layer of cells, ganglion cells, are
  activated
• Axons of ganglion cells make up optic nerve that
  sends impulses to the lateral geniculate nucleus
  (LGN) of the thalamus
• Messages are then sent to the visual cortices in
  the occipital lobes
• Spot where optic nerve leaves the retina has no
  rods or cones, so called the blind spot
• Impulses from left side of each retina go to left
  hemisphere of brain impulses from right side of
  each retina go to right hemisphere where the
  nerves cross each other, called the optic chiasm

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Energy Sources Vision

• Step 4 in the brain
• Visual cortex of the brain is located in the
  occipital lobe
• Visual cortex receives impulses from cells of
  retina, and activate feature detectors
• Visual cortex has feature detectors for vertical
  lines, curves, motion, and other features of
  images

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Theories of Color Vision Trichromatic Theory

• Oldest and most simple theory
• Hypothesizes that we have 3 types of cones in the
  retina that detect the colors blue, red and green
• Cones are activated in different combinations to
  produce all the colors of the visual spectrum
• Cannot explain afterimages or color blindness

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Theories of Color Vision Opponent-Process Theory

• States that sensory receptors arranged in the
  retina come in pairs red/green pairs,
  yellow/blue pairs, and black/white pairs
• If one sensor is stimulated, its pair is
  inhibited from firing
• Explains afterimagesstare at a color, the cones
  for that color will fatigue shift gaze and
  opponent part of the pair will fire
• Also explains color blindnesspeople
  w/dichromatic color blindness have trouble seeing
  red/green or yellow/blue
• Note both theories are needed

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Energy Senses Hearing

• Sound waves are created by vibrations traveling
  through the air, collected by ears
• Vibrations go thru process of transduction into
  neural messages sent to brain
• Amplitude (height) of sound wave determines
  loudness, measured in decibels frequency
  (length) determines pitch, measured in megahertz
• Sound waves collected in outer ear (pinna),
  travel down auditory canal until they reach the
  eardrum (tympanic membrane)
• Eardrum vibrates as sound waves hit is
  connected to the 1st in a series of 3 small
  bones, called ossicles
• Eardrum connects to hammer (malleus), which is
  connected to the anvil (incus), which connects to
  the stirrup (stapes)
• Ossicles transmit vibration of eardrum to the
  oval window, membrane similar to eardrum
• Oval window attached to the cochlea, looks like
  snails shell and filled w/fluid as oval window
  vibrates, fluid moves
• Floor of cochlea is the basilar membrane, lined
  w/hair cells connected to the organ of Corti,
  which are neurons activated by movement of hair
  cells
• When fluid moves, hair cells move, transduction
  occursorgan of Corti fires and impulses are
  transmitted to brain via auditory nerve

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Pitch Theories

• Place Theorysays that hair cells in the cochlea
  respond to different frequencies of sound
  depending on where they are located in the
  cochlea
• Some bend in response to high pitches, some to
  low
• We sense pitch because hair cells move in
  different places in the cochlea
• Frequency Theoryresearch shows that place theory
  explains sensation of upper ranges of pitch, but
  not lower lower tones sensed by the rate at
  which cells fire
• We sense pitch because the hair cells fire at
  different frequencies in the cochlea

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Deafness

• Conduction deafnesssomething goes wrong with the
  system of conducting sound to cochlea
• Nerve (sensorineural) deafnessoccurs when the
  hair cells in the cochlea are damaged, usually by
  loud noise difficult to treat because hair cells
  do not regenerate

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Energy Senses Touch

• When our skin is indented, pierced, or
  experiences a change in temperature, our sense of
  touch is activated
• Some nerve endings in skin respond to pressure,
  and some to temperature
• Brain senses intensity of touch and placement of
  touch
• If touch or temperature receptors are stimulated
  sharply, pain receptors will also fire
• Gate-control theoryexplains that some pain
  messages have a higher priority than others when
  higher priority message is sent, gate swings open
  for it, and swings shut for lower priority
  message which we wont feel
• Endorphins will also swing the gate shut

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Chemical Senses Taste (Gustation)

• Chemicals from food we eat are absorbed by taste
  buds on tongue
• Taste buds are located on papillae, the bumps you
  can see on tongue
• Taste buds are located all over the tongue and
  some parts of the inside of cheeks and roof of
  mouth
• Humans sense four different types of tastes
  sweet, salty, sour, bitter
• Some taste buds respond more intensely to a
  specific taste
• People differ in ability to tastemore densely
  packed the taste buds, the more chemicals are
  absorbed, more intensely food is tasted
• What we think of as the flavor of food is a
  combination of taste and smell

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Chemical Senses Smell (Olfaction)

• Molecules of substances rise into the air and
  some are drawn into our nose
• Molecules settle in a mucous membrane at the top
  of each nostril and are absorbed by receptor
  cells
• Receptor cells are linked to the olfactory bulb,
  which gathers the messages from the olfactory
  receptor cells and sends to brain
• Nerve fibers from the olfactory bulb connect to
  brain at amygdala and then hippocampus, which
  make up limbic systemseat of emotion and memory
  (all other sensory info is routed thru thalamus)
• Direct communication with limbic system may
  explain why smell is such a powerful trigger for
  memories

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Body Position Senses

• Vestibular sensetells us about how our body is
  oriented in space
• 3 semicircular canals in the inner ear, filled
  w/fluid, give brain feedback about body
  orientation
• When position of head changes, fluid moves,
  activating neurons, and impulses go to brain
• Kinesthetic sensegives us feedback about the
  position and orientation of specific body parts
• Receptors in muscles and joints send info to
  brain about our limbs
• This info, combined w/visual feedback, lets us
  keep track of our body

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Perception

• Perceptionprocess of understanding and
  interpreting sensations
• Psychophysicsstudy of the interaction between
  sensations we receive and our experiences of them

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Thresholds

• Absolute thresholdsmallest amount of a stimulus
  we can detect 50 of the time
• Subliminalstimuli below absolute threshold
• Just-noticeable differencesmallest amount of
  change needed in a stimulus before we detect a
  change computed by
• Webers lawthe change needed is proportional to
  the original intensity of the stimulus the more
  intense the original stimulus, the more it will
  need to change before we notice a difference

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Perceptual Theories

• Signal Detection Theoryinvestigates the effects
  of distractions and interference we experience
  while perceiving the world
• Takes into account how motivated we are to detect
  certain stimuli and what we expect to
  perceiveresponse criteria
• Tries to explain and predict the different
  perceptual mistakes we make
• False positivewe think we perceive something
  that isnt there
• False negativenot perceiving a stimulus that is
  there

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Perceptual Theories

• Top-down processingwe perceive by filling in
  gaps in what we sense
• We use background knowledge to fill in the gaps
• i.e. I _ope you_ _et a 5 on t_ _ A_ e_am.
• Our experience creates schematamental
  representations of how we expect the world to be
• Schemata can create a perceptual
  setpredisposition to perceiving something in a
  certain way
• i.e. 1970s, some parent groups were concerned
  about backmaskingsupposed hidden messages
  recorded backwards in music
• Lyrics played backwards are random noise, but if
  you expect to hear something threatening, you
  probably will
• People who listened to the songs played backward
  and had schemata of this music as dangerous or
  evil perceived the threatening messages due to
  top-down processing

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Perceptual Theories

• Bottom-up processing (feature analysis)we use
  only the feature of the object itself to build a
  complete perception opposite of top-down
• Start perception at the bottom with the
  individual characteristics of the image and put
  all together into final perception
• We constantly use both top-down and bottom-up
• Top-down is faster, but more prone to error
  bottom-up takes longer, but more accurate

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Principles of Visual Perception

• Figure-ground relationshipwhat part of a visual
  image is the figure, and what part is the
  background
• Gestalt ruleswe normally perceive images as
  groups, not isolated elements we group objects
  according to
• Proximityobjects close together
• Similarityobjects similar in appearance
• Continuityobjects that form a continuous form
• Closureobjects that make up a recognizable
  image, even if they have gaps

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Principles of Visual Perception

• Constancyability to maintain constant perception
  even though every object we see changes minutely
  from moment to moment due to our changing angle
  of vision, variations in light, etc
• Size constancyobjects closer to our eyes produce
  bigger images on retinas, but we know objects
  dont grow or shrink in size as they move closer
  or farther away
• Shape constancyobjects viewed from different
  angles produce different shapes on retinas
• Brightness constancywe perceive objects as being
  a constant color even as light reflecting off the
  object changes

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Principles of Visual Perception

• Perceived motionour brains are able to detect
  how fast images move across retinas and take in
  account our own movement
• In some situations, we perceive movement that
  doesnt exist
• Stroboscopic effectused in movies or flip books
  images in a series of still pictures presented at
  a certain speed will appear to be moving
• Phi phenomenona series of lightbulbs turned on
  and off at a particular rate will appear to be
  one moving light
• Autokinetic effectis a spot of light is
  projected steadily onto the same place on a wall
  of an otherwise dark room and people are asked to
  stare at it, they will report seeing it move

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Principles of Visual Perception

• Depth cuesw/o depth perception, we would
  perceive the world as 2-dimensional flat surface,
  unable to differentiate between what is near and
  what is far
• Visual cliff experimentinfants placed on one
  side of a glass-topped table that creates the
  impression of a cliff infants old enough to
  crawl will not crawl across the visual cliff,
  implying depth perception
• Monocular cuesdepth cues that do not require
  having 2 eyes include linear perspective,
  relative size cues, interposition cues, texture
  gradient, and shadowing
• Binocular cuesdepth cues that depend on having 2
  eyes include binocular disparity (retinal
  disparity) and convergence