Sensation and Perception

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Sensation and Perception
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• Without sensation and perception, you could not
  read this book, find food, communicate with
  others, or experience any of the joys or
  challenges of life.
• With no vision, no hearing, no smell, no taste,
  no touch, or movement, you would not be able to
  make sense of the world outside of your body.
•  

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• Once we take information in through our senses,
  we do something with it to interpret it. What we
  do depends on many factors like our mood, the
  circumstances, or even our cultural background.
•  Your nervous system sorts through all of this
  incoming information and analyzes the stimuli
  entering through your many sensory systems. It
  is automatic.

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• The analysis that takes place during this
  processing is part of perception, our
  interpretation of the incoming sensory
  information. Perception reflects learning,
  expectations, and attitudes.
• Stimulation of the senses and the ways in which
  people interpret that stimulation is affected by
  several concepts. These concepts include
  absolute threshold, difference threshold,
  signal-detection theory, and sensory adaptation.

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• Absolute Threshold the weakest amount on
  stimulus that can be seen.
• Difference Threshold the ability to detect the
  changing levels of a stimulus.
• Signal-Detection Theory a method of
  distinguishing sensory stimuli that takes into
  account not only their strengths but also such
  elements as the setting, your physical state,
  your mood, and your attitudes.

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• People are quicker to detect a signal among noise
  when
• they expect the signal
• it is important that the signal is detected
• they are alert
• Experience matters in detecting signals
• 10 hours of playing an action video game
  increased novice players signal detection skills.

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• Sensory Adaptation the process by which we
  become more sensitive to weak stimuli and less
  sensitive to unchanging stimuli.
• VISION - Many of us consider vision to be the
  most essential of our senses. No other sense
  allows us to gather so much information from
  nearby and distant sources.

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• Light enters the eye as waves of electromagnetic
  energy, part of a broad, ever-present spectrum of
  electromagnetic radiation in our environment.
• The light is projected onto a surface. The
  amount of light that enters is determined by the
  size of the opening in the colored part of the
  eye, the pupil.

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• The pupil admits light into the inner portion of
  the eye, where it encounters the lens which
  adjusts to the distance of objects by changing
  its thickness.
• These changes project a clear image of the object
  onto the retina, which is the part of the eye
  that acts like the film in a camera.

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• The retinas photoreceptors hands off the image
  to a nerve that carries the visual input to the
  brain the visual area called the occipital
  lobe. 
• We have a blind spot where the optic nerve leaves
  the eye because this area lacks photoreceptors.
• There are two different types of photoreceptor
  cells rods and cones that differ in both
  appearance and in function.

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• Rods can detect only black, white, and shades of
  gray because they are sensitive to bright light.
  Cones provide color vision, but only if there is
  enough light.
• Adaptation to bright light happens much more
  quickly than adaptation to dark light. Dark
  adaptation begins within a few minutes and
  continues to improve for up to 45 minutes.

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• Bright light adaptation may hurt initially, but
  takes place within a couple of minutes. 
• Visual acuity is determined by the ability to see
  visual details.
• The Snellen Chart is used by eye doctors to test
  your vision. As people age, the lenses in the
  eyes become more brittle and make focusing more
  difficult. Thus, they become far-sighted.
  Usually this starts around middle age.

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• The wavelength of light determines the color.
  People with normal color vision see any color in
  the spectrum of visible light.
• Cones, one of the two types of photoreceptors in
  the retina of the eye, enable us to perceive
  color.
• Some are sensitive to blue, some to green, and
  some to red. When more than one kind of cone is
  stimulated at the same time, we perceive other
  colors of the spectrum.

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• Afterimages occur after staring at an image for a
  short period of time and then looking away. The
  image will be in a complimentary color.
• People who are color blind are partially or
  totally unable to distinguish color due to an
  absence or, or malfunction, in the cones.
  Really, they are just limited in the number or
  colors that they see.

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• Objects do not possess color (in a sense, the
  tomato isnt red, its everything but red...)
• long wavelengths of red light are rejected
  (reflected) from the tomato
• The rays are not colored.
• Color is a product of our brains transduction of
  light waves.
• JND so low that we can discriminate between over
  7 million colors.

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• Generally, color blind people lack either the red
  or green receptors and have trouble telling the
  difference between the two.
• This is an inherited condition and is much more
  common among males than females. Many times, the
  person does not even realize that it exists.

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• HEARING - Sound comes in waves that are produced
  by vibration. Each of these vibrations is called
  a cycle or a sound wave. Every sound has its own
  pitch and loudness.
• The length of the wave determines the pitch of
  the sound. The more cycles per second
  (frequency), the higher the pitch of a sound.

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• The human ear can hear sound waves that vary from
  20 to 20,000 cycles per second (frequency). Many
  animals hear sounds well beyond that limit.
• The height (amplitude) of a wave determines its
  loudness. Loudness is measured in decibels.
  Zero decibels (dB) is considered the threshold of
  hearing.

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• Any prolonged sound over 85 dB can produce
  hearing loss.
• The ear is shaped to capture sound waves. What
  we normally think of as the ear is actually the
  outer ear.
• The middle ear is a thin membrane that vibrates
  when sound waves strike it. As it vibrates, it
  transmits the sound to three small bones the
  hammer, the anvil, and the stirrup.

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• These bones vibrate and transmit sound to the
  inner ear, where the cochleas neurons move in
  response to the vibrations of its fluids.
• The movement generates neural impulses that are
  transmitted to the brain via the auditory nerve.
  Auditory input in projected onto the hearing
  areas of the cerebral cortex.

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• How do we locate where a sound is coming from?
  Step one is to determine which ear hears the
  sound first. Sound travels through air at about
  750 miles per hour.
• Step two is to determine which ear hears the
  louder, more intense sound.

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• About 2 million Americans experience deafness,
  which can be inherited or caused by disease,
  injury, or old age.
• Conductive deafness occurs because of damage to
  the middle ear and can usually be helped by using
  hearing aids.
• Sensorineural deafness is caused by damage to the
  inner ear. If the auditory nerve is not damaged,
  some help might be obtained from a cochlear
  implant.

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• SMELL - People do not have as strong a sense of
  smell as many animals. Smell is a chemical
  sense.
• Molecules given off by many substances circulate
  in the air.
• When these molecules reach the upper nasal
  passages, olfactory cells that project from the
  brain can process them.

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• By triggering various combinations of olfactory
  cells, thousands of different odors are
  detectable.
• These cells do not regenerate when damaged, so
  many elderly individuals have a noticeably
  decreased sense of smell.

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• TASTE - Taste is also a chemical sense. You have
  receptor cells located on the surface of the
  tongue that respond to the chemical structure of
  the foods you eat. These cells can detect four
  different tastes salty, sweet, sour, and
  bitter.

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• Taste buds that are responsive to sweetness are
  located at the tip of the tongue. Receptors for
  bitterness are at the back of the tongue.
• Sourness is sensed along the sides of the tongue,
  and saltiness overlaps the areas sensitive to
  sweetness and sourness.

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• Taste buds are composed of groups of between 50
  and 150 columnar taste receptor cells bundled
  together like a cluster of bananas.
• The taste receptor cells within a bud are
  arranged such that their tips form a small taste
  pore, and through this pore extend microvilli
  from the taste cells. The microvilli of the taste
  cells bear taste receptors.

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• Among humans, there is substantial difference in
  taste sensitivity. Roughly one in four people is
  a "supertaster" that is several times more
  sensitive to bitter and other tastes than those
  that taste poorly.
• Taste receptors can be damaged by heat.
  Fortunately, they do replace themselves within a
  few days.

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• It is also clear that the sense of smell
  profoundly affects the sensation of taste. Think
  about how tastes are blunted and sometimes
  different when your sense of smell is disrupted
  due to a cold.

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• SKIN SENSES - Touch is a combination of pressure,
  temperature, and pain. It is our physical
  connection with the outside world.
• The four basic skin senses are pain, warmth,
  cold, and pressure. Your experience of other
  skin sensations flows from various combinations
  of these four basic senses.

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• Different parts of the body are more sensitive to
  pressure than others. The fingertips, lips,
  nose, and cheeks are more sensitive than the
  shoulders, thighs, and calves.
• The receptors are just beneath the skin. When
  skin temperature increases because you touch
  something warm, receptors for warmth fire.
  Decreases in skin temperature cause receptors for
  cold to fire.

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• The pain message is sent from the point of
  contact to the spinal cord to the thalamus in the
  brain. Then it is projected to the cerebral
  cortex, where the person registers the location
  and severity of the brain.
• Chemicals called prostaglandins help the body
  transmit pain messages to the brain.

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• The Gate Theory suggests that only a certain
  amount of information can be processed by the
  nervous system at a time.
• Rubbing, scratching, or icing and injured area
  partially blocks the sensation of pain by
  competing with the pain message for space.

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• Phantom limb pain appears to reflect the activity
  of the neurons in the brain that store memories
  connected with the missing limb. 
• BODY SENSES  - Without other body senses, you
  would have to pay attention just to keep your
  balance, lift your leg to climb stairs, or even
  to get food into your mouth.

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• The vestibular sense, located in your inner ear,
  provides information about your overall
  orientation. It enables you to keep your
  balance, tells you whether you are upside-down,
  and lets you know if you are falling.
• Kinesthesis is the sense that informs people
  about the position and motion of parts of their
  bodies. It relies on receptor cells located
  throughout your muscles, tendons, and joints.

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• PERCEPTION - Perception is the way that we
  organize or make sense of our sensory
  impressions.
• Gestalt psychologists used the following rules of
  perceptual organization to make sense of sensory
  information
• 1. Closure the tendency to perceive a complete
  or whole figure even when there are gaps in what
  your senses tell you.

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• 2. Figure-Ground Perception the perception of
  figures against a background. We experience this
  every day. Objects that draw your attention will
  be nearer to the center of the visual field than
  the edge. It may be moving, and it will often be
  fairly large and colorful.

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• 3. Proximity nearness. If objects are close
  together, we place them in the same group.
• 4. Similarity people think of similar objects
  as belonging together.
• 5. Continuity your brain assumes movement
  continues in a particular direction unchanged.
  People prefer smooth, continuous patterns.

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• 6. Common Fate things moving together must
  belong together or have a common purpose.
• To be able to sense movement, humans need to see
  an object change its position relative to other
  objects. (We dont feel earth move.) You can
  look for objects that are stable, like buildings.
  You can also close your eyes and try to sense
  motion.

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• Psychologists have also studied illusions of
  movement, such as stroboscopic motion. This is
  produced by showing the rapid progression of
  images or objects that are not moving at all.
• Movies work in this way. Because of the law of
  continuity, humans prefer to see things as one
  continuous image. Perception smoothes over the
  interruptions and fills in the gaps.

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• Depth perception is very important.
• Depth in this case means distance away. You
  would not be able to drive a car, catch a ball,
  shoot a free throw, thread a needle, or place
  clean dishes on a shelf without it.
• You use both monocular and binocular cues.

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• Monocular cues need only one eye to be perceived.
  They cause certain objects to appear more
  distant from the viewer by using perspective,
  clearness, overlapping, shadow, and texture
  gradient.
• 1. Perspective objects that are farther away
  will stimulate a smaller area of your retina than
  the one that is near. We also use our experience
  to judge its distance.

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• 2. Clearness nearby objects appear to be
  clearer, and we see more details, thus they
  appear to be closer to us.
• 3. Overlapping this is the placing of one
  object over another. Experience teaches us to
  perceive partly covered objects as being farther
  away than the objects that block them from view.

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• 4. Shadows give us information about objects
  three dimensional shapes and where they are
  placed in relation to the source of light.
• 5. Texture Gradient texture is the surface
  quality and appearance of an object, while
  gradient is a progressive change. Closer objects
  are perceived a having a more varied texture than
  objects that are farther away.

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• 6. Motion Parallex the most complex of
  monocular cues. It involves the image of
  something as the viewer moves. Objects seem to
  move forward or backward depending on how far
  away they are from the viewer.

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• Binocular cues require both eyes for depth
  perception.
• 1. Retinal disparity serves as a cue for depth
  only for objects that are within a few feet of
  us. It is the difference between the images you
  see with the retinas in your left and right eyes.
  

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• 2. Convergence translates tension in the
  muscles that control your eyeballs into
  information about distance. To maintain your
  focus on an object as it moves closer to you,
  your eyes have to swing inward, or converge on
  it, giving us a cross-eyed look.

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• Perceptual constancies require us to use our
  experiences.
• 1. Size objects further away seem smaller and
  do not take up much room on our retina. Our
  perspective teaches us that objects size remain
  constant.
• 2. Color objects maintain their color, even in
  different light.

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• 3. Brightness the tendency to perceive an
  object as being equally bright, even when the
  intensity of the light around it changes.
• 4. Shape the knowledge that an item only has
  one shape no matter what angle you view the item
  from.
• Visual illusions are the result of your brains
  use of perceptual constancies.