Sensation and Perception

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Sensation and Perception
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Sensation

• The process of detecting sights, sounds, smells,
  heat, pressure, or movement

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Perception

• The process of integrating, organizing, and
  interpreting sensations
• Happens in brain

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How Sensation Works

• Energy from our environment is detected by
  specialized sensory receptors
• This energy is converted into neural impulses

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• This process is known as transduction
• These signals are sent to your brain
• The information is then interpreted

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Thresholds

• What is the minimum amount of energy required to
  detect a sensation in our environment
• Two types of thresholds

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Absolute Threshold

• The minimum stimulation needed to detect a
  sensation half of the time
• Examples of absolute thresholds

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• A candle seen from 30 miles away on a clear, dark
  night
• A tick of a watch at 20 feet
• One teaspoon of sugar dissolved in two gallons of
  water

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• One drop of perfume diffused throughout a
  three-room apartment
• A bees wing falling on your cheek from a height
  of 1/2 inch

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Difference Threshold

• The smallest difference that can be detected
  between two different stimuli half of the time
• A.k.a. Just noticeable difference

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• Examples- Lifting weights- what is the smallest
  amount that can be added and still be detected
• Difference between eggshell and off-white

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Webers Law

• The difference threshold will vary depending on
  its strength to the original stimulus
• Sensation is relative

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• Example- Lifting weights
• If you are lifting 50 lbs. And somebody adds 10
  lbs, you will notice the change
• If you are lifting 500lbs. And somebody adds 10
  lbs., you will not notice the change

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Sensory Adaptation

• If we are exposed to the same stimuli for long
  periods of time, we get used to it
• Our sensory cells become less sensitive to that
  specific stimulus

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• Examples- Annoying sounds- noise from the
  highway, gunshots, the rooster in my back yard
• Smells- Cattle, the cafeteria smell
• Touch- sitting in a chair

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Vision

• The process we use to turn light from a physical
  energy to a mental perception

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The Human Eye

• Cornea- Clear membrane that covers the eye
• Pupil- Black opening where light enters the eye
• Iris- colored part of your eye

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• Lens- focuses light on the retina
• Retina- Thin, light-sensitive membrane that
  covers most of the inner eye
• Retina is made up of sensory cells called rods
  and cones

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Rods

• 125 million rods in each eye
• Very good at detecting light
• Used primarily for low light vision
• React slowly to changes in light- 30 minutes

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Cones

• Cones differentiate colors- thus are primarily
  involved in color vision
• Need a lot of light to function
• Are very good at detecting fine details

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Rods
Cones
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Fovea

• Small area on the retina, largest concentration
  of cones on the retina
• Rods increase as you get away from the fovea

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Night Vision

• Since rods are used to see in low-light
  conditions, we can see better at night if we use
  our peripheral vision (look to the side of
  something)

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Blind Spot

• Where the optic nerve connects to the eye, we
  have no rods or cones
• This creates a gap in our field of vision

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• Our brain will fill in the missing information

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Processing Information

• Most processing occurs in the brain, though some
  processing happens along the way

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Bipolar Cells

• Connected to rods and cones
• Act as an information bridge

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Ganglion Cells

• Connected to bipolar cells
• One or two cones are connected to each ganglion
  cell
• Hundreds of rods may be connected to one ganglion
  cell

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Optic Nerve

• Made up of axons from ganglion cells
• Connects eyes to your brain
• About the size of a pencil

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Color Vision

• Definitions of color characteristics
• Hue Different wavelengths of light are perceived
  as different colors

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• Saturation Purity of light (how rich and vivid a
  color is)
• Brightness How intense a light is
• These characteristics can produce over 1 million
  colors that can be experienced by humans

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Why is an Orange Orange?

• The orange absorbs all wavelengths of light
  except orange (orange is reflected)
• White colors reflect all light
• Black colors absorb all light

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How do we see color?
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Trichromatic Theory

• There are three varieties of cones red, green,
  and blue
• Each of these types are VERY sensitive to one of
  the colors, and partially sensitive to others

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• When one color strikes the retina, it triggers a
  combination of different cones
• Example- Purple light triggers blue-sensitive and
  red-sensitive cones

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• Easy to explain color blindness
• People with red-green color blindness lack either
  red or green cones
• Color blindness is genetic

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• About 8 of males are color blind
• About 1/2 of females are color blind
• Total color blindness is found in 1 out of
  100,000 people

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Opponent-Process Theory

• There are four basic colors
• These colors are divided into pairs
• Red and Green
• Blue and Yellow

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• If red-green cones see a red color, they send a
  red signal to the brain (green signals are
  inhibited)
• Green and red cannot be stimulated together
• Purple is a combination of red signals and blue
  signals

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• Opponent-Process theory explains afterimages
• When you stare at something for a long time, then
  stare at a white space, youll see the image in
  opposite colors

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Hearing
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The Nature of Sound

• Hearing a.k.a. audition
• Amplitude- Intensity of sound (how loud it is)
• Measured in decibels
• Zero represents the average human absolute
  threshold

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• Pitch- refers to the relative highness or
  lowness of a sound
• Determined by the frequency of the sound
• Measured in Hertz- waves per second

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• Timbre- What lumberjacks say when a tree is
  falling
• Actually, timbre refers to the combination of
  frequencies that make up any given sound

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How We Hear

• There are three major parts of the ear Outer,
  middle, and inner
• Outer Ear- Consists of pinna, ear canal, and
  eardrum
• Collects sound

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• Sound waves are collected by the pinna and causes
  the eardrum to vibrate
• Middle Ear- consists of the hammer, anvil, and
  stirrup
• Vibrations from eardrum cause these bones to
  vibrate

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• These vibrations are transferred to the oval
  window (membrane)
• Inner Ear- Consists of Cochlea
• Cochlea contains the basilar membrane

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• Basilar membrane is lined with hair cells
• When vibrations come from the oval window, they
  bend the hair cells
• The bending of the hair cells cause a neural
  impulse to be sent to the brain

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Hearing Loss

• Conduction Deafness- Caused by problems in the
  middle ear
• Usually associated with old age
• Can be corrected with a hearing aid

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• Nerve deafness- caused by damage to the hair
  cells
• Usually caused by exposure to loud noises
• Ringing in your ears

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Chemical Senses

• Includes smell and taste
• Involves the detection and interpretation of
  various chemicals

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Smell

• Olfactory receptor cells are responsible for
  detecting smells in the environment
• They detect chemical molecules that are emitted
  from various sources

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• Olfactory receptors are located throughout your
  nose
• You have different receptors for different
  molecules
• We have identified hundreds of different
  olfactory receptors

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Odor Sensitivity

• Women typically have much better senses of smell
  than men
• Olfactory ability decreases with age

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• Humans are highly sensitive to odors, but many
  animals are more sensitive
• Humans 10 million olfactory receptors
• Dogs 200 million olfactory receptors

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Smelly Research

• Parents were able to identify a t-shirt worn by
  their children over t-shirts worn by unrelated
  children with 95 accuracy (Porter Moore, 1981)

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Taste

• Results from the stimulation of taste receptors
  in your mouth
• Saliva dissolves substances, releasing chemicals
  that are detected

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Taste Buds

• Line our throat, cheeks, roof of our mouth, and
  tongue
• Each taste bud contains about 50 receptor cells
• When taste buds are stimulated, they send a
  signal to the brain

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• There are five tastes that we can detect
• Sweet
• Sour
• Bitter
• Salty
• Umami or savory(aged cheese flavor)

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Brush your teeth, drink OJ...

• Why is it bitter?
• A chemical in most brands of toothpaste
  intensifies bitter tastes while inhibiting sweet
  substances from bonding with taste receptors

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Skin and Body Senses

• Skin senses- Includes touch, temperature, and
  pain
• Body senses- Includes movement, position, and
  balance

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Touch And Temperature

• Our skin is our largest sense organ
• Covers 20 square feet, weighs about 6 pounds

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Touch

• Touch sensations are registered as pressure
• Registered by Pacinian Corpusles, which lie
  within your skin
• Sensitivity to pressure can undergo sensory
  adaptation

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Temperature

• Our skin is divided into small patches that can
  detect warm or cold sensations
• Cold spots can be stimulated by hot temperatures
  (over 125 degrees)

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• We experience hot sensations when both warm and
  cold spots are activated

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Pain

• Pain is important to our survival
• It alerts us to something that may be injuring us

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Most Sensitive Areas (Pain)

• Back of knee
• Neck
• Bend of the elbow

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Least Sensitive Areas (Pain)

• Tip of nose
• Sole of foot
• Ball of thumb

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Pain Control

• Gate-Control Theory
• Pain is controlled by a series of gates in the
  spinal cord
• If the gate is open, pain is experienced

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• If the gate is closed, no pain is experienced
• Substance P- Neurotransmitter that is released in
  the spinal cord
• Responsible for sending pain signals to the
  brain

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• There is a lot of variability in the pain
  experience
• Many factors can influence how pain is
  experienced
• We shall discuss these after the experiment...

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• Anxiety, fear, and a sense of helplessness, and
  increased heart rate all increase the sensation
  of pain
• Positive emotions, laughter, distraction, and a
  sense of control can decrease the sensation of
  pain

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Why?

• The release of endorphines occurs in certain
  psychological states
• What techniques can we use to reduce pain?

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Distraction

• Actively focus on some non-painful stimulus
• Count backwards by 7, listen to music, count
  ceiling tiles, etc.

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Imagery

• Form a vivid mental image
• Examples- walking on a beach, driving a car,
  hiking in the mountains, etc.
• Imagine all aspects of the scenario- sights,
  sounds, aromas, touches, and tastes

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Positive Self-Talk

• Make positive coping statements
• I feel pain, but Im in control.

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Counterirritation

• Create a strong, competing sensation that is
  mildly stimulating or irritating
• Rubbing an area where an injury has occurred,
  biting your lip, etc.

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Relaxation

• Deep relaxation can reduce pain
• Deep breathing is a very simple way to accomplish
  this

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Movement, Position, and Balance

• Controls your body
• Kinesthetic sense- Involves the location and
  position of body parts in relation to each other

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• Kinesthetic sense is controlled by proprioceptors
• These are specialized receptor cells located in
  muscles and joints

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Vestibular Sense

• Provides sense of balance
• Controlled by semicircular canals and vestibular
  sacs
• Fluid filled sacs that contain hair-like receptor
  cells

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• When our body is in motion, the fluid moves the
  cells, which produce motion senses
• Our eyes are also responsible for some motion
  information
• Motion Sickness

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Perception
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Definition Again

• Perception refers to the process of integrating,
  organizing, and interpreting sensory information
  into meaningful representations
• Perceptual processes tell us three things

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• 1- What is it?
• 2- How far away is it?
• 3- Where is it going?
• Study of perception was popularized by the
  Gestalt psychologists in early 1900s
• They emphasized how we see WHOLE objects, not the
  PARTS of objects

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Perception of Shape

• We rely on an objects shape to identify what it
  is
• Three year olds will identify an object by shape
  over other features (color, size, etc.)

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Figure/ Ground Relationship

• We automatically separate things that stand out
  (foreground and background)
• Things in the background appear fuzzy
• Different neurons in brain fire when looking at
  foreground and background

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• Sometimes, we cannot separate figure from ground
• Known as figure-ground reversal

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• Real world example- camouflage

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Perceptual Grouping

• We actively try to organize the stuff we see
• Allows us to have stable perceptions of whole
  objects
• Similarity- we perceive objects of a similar
  shape, color, or size as a single figure

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• Closure- We tend to fill in gaps or contours in
  an incomplete image

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• Good Continuation- We view elements that appear
  to follow the same direction as a single unit

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• Proximity- We perceive objects that are close
  together as a single unit or figure

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Depth Perception

• Being able to perceive depth is very important to
  humans
• Monocular cues- Only require one eye
• Relative size- If two objects are assumed to be
  similar in size, the object that seems larger is
  assumed to be closer

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• Overlap- If one object partially blocks another,
  we assume it is in front

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• Arial perspective- Faraway objects appear hazy or
  blurry because of the atmosphere

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• Texture gradient- Details on the surface of
  objects fade out as they get farther away

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• Linear Perspective- Parallel lines seem to meet
  in the distance

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• Motion Parallax- While in motion, objects close
  to you seem to move by faster, distant objects
  move more slowly

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Binocular Cues

• Depth cues that require both eyes
• Convergence- As your eye muscles move your eyes
  inward, whatever you focus on is perceived as
  being closer

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• Binocular disparity- Since our eyes are about 2
  apart, each sees a slightly different image
• When images are very different, we perceive
  object as closer
• When images are very similar, we perceive object
  as further away

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• Stereograms picture that used retinal disparity
  to create illusion of three dimensions on a two
  dimensional picture
• The trick- focus your eyes as if you were looking
  at an object in the distance
• Causes two different images to form in stereogram

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• Brain fuses the images, creating the altered
  perception

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Perceptual Illusions

• Sometimes, we misperceive the true
  characteristics of an object or an image
• Muller-Lyer Illusion

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• We perceive the top line as being longer than the
  bottom

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• Moon illusion- The moon looks larger near the
  horizon than it does in the sky

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• Ponzo illusion

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• Poggendorff Illusion-

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• Hermann Grid Illusion

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The Blakemore-Sutton Effect
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The Blakemore-Sutton Effect
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The Blakemore-Sutton Effect
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Impossible figures

• Mess around with our perceptions
• Some examples

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• An interesting example of perception

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Another real-life Contextual Set
Our eyes are drawn to the police (people) and the
truck, and the storm drain (because it is in the
center of the picture and contrasts with the
darker parts around).
Can you figure out what happened to the truck?
USE CONTEXTUAL CLUES to arrive at your
understanding.
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Another real-life Contextual Set
This pickup broke through the barrier at the
upper right (with lots of police) and flipped
across the storm drain, landing upright on the
other side.
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Another real-life Contextual Set
We did not notice the area below the storm drain,
which might have tipped us off that there was
more going on in the context than what at first
appeared. We simply and characteristically
looked at the apparent story of this
picturethe truck accident. In this longer-view
image, our eyes are drawn to the cliff directly
below the storm drain, which the truck flipped
over, avoiding disaster.
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• A test used to measure our perceptual abilities
  (it gives us clues as to how our brain works)

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• Green
• Red
• Blue
• Black
• Blue
• Red
• Green
• Black
• Red
• Blue

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• Black
• Red
• Blue
• Black
• Blue
• Red
• Green
• Green
• Red
• Blue

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• Truck
• Top
• Couch
• Hand
• Couch
• Top
• Truck
• Top
• Hand
• Couch