Sensation and Perception

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Sensation and Perception

• True or False???
• On a clear, dark night most of us can see a
  candle flame 30 miles away.
• Advertisers are able to shape our buying habits
  through subliminal messages.
• Constant eye movements prevent our vision from
  being seriously disrupted.

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Introducing,.Sensation!

• Seeing is believing.
• For each of the following visuals, simply write
  down what you see. (Do not share with your
  neighbor.)

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Analyzing what we see.

• Each visual provides sensory information that
  gives rise to two totally different perceptual
  interpretations.
• Now, lets try it again
• Write down what you see first in the next visual
  image.

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Sensation and visual images

• Why is it that no matter how many times we look
  at the image, we tend to see the image we saw the
  first time we observed it?
• First impression schema
• Have to consciously seek the other figure
• After practice, we can see both images, but not
  simultaneously

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So, what is Sensation Perception?

• Sensation
• The physical energy we detect (with our senses)
  from the environment and encode as neural
  impulses (what we sense and send to the brain)
• Perception
• How we select, interpret and organize our
  sensations (how the brain interprets it)

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In other words

• Sensation provides the raw information that
  perception translates into our experiences

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Sensation The
Forest Has Eyes

• sensation and perception work together to sort
  out complex processes

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Sensation and Perception(Work together)

• Bottom-Up Processing (Sensation)
• Sense receptors detect stimuli and send to the
  brain
• the brain then integrates sensory information
• Top-Down Processing (Perception)
• information processing guided by higher-level
  mental processes
• How we interpret sensations based on
  expectations and previous experiences

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Top Down Processing

• Aoccdrnig to rscheearch at Cmabridge Uinervtisy,
  it deosnt mttaer in what oredr the ltteers in a
  word are, the olny iprmoetnt tihng is that the
  frist and lsat ltteer be at the rghit pclae. The
  rset can be a total mses and you can still raed
  it wouthit a porbelm. This is bcuseae the huamn
  mnid deos not raed ervey lteter by istlef, but
  the word as a wlohe.

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Top Down Processing

• How were you able to immediately make sense of
  these scrambled words?
• Our experience and expectations enable us to
  immediately perceive the scrambled letters as
  meaningful words and sentences.
• IOW Higher level processes guide our perceptions.

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Distinguishing Between Sensation and Perception

• See Handout
• Blotch (5.2)
• Fraser Spiral (5.2)
• Place one finger on any line composing the
  spiral.
• Place a finger from your other hand beside it and
  begin tracing the circle while holding your first
  finger in place.
• What happens?

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Failures of Perception

• Prosopagnosia complete sensation but incomplete
  perception (face blindness)
• Can sense visual information, but cant recognize
  it (cant relate stored knowledge to sensory
  input)
• Damage to temporal lobe area (recognition)

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Sensation- Basic Principles

• Psychophysics
• study of how physical energy relates to our
  psychological experience (Or study of
  interaction between sensations we receive and our
  experience of them.)
• Light- brightness
• Sound- volume
• Pressure- weight
• Taste- sweetness

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Gustav FechnerPioneer in Psychophysics

• 1801-1887 (U. of Leipzig)
• Theory consciousness and matter coexist
• Mind / body two aspects of fundamental unity
• Stared at sun! Afterimage of blue and yellow
• Mathematical relationship b/n force of stimuli
  and intensity of sensation

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Sensation- Thresholds

• Absolute Threshold
• minimum amount of stimulus one can detect 50 of
  the time
• Difference Threshold
• minimum difference between two stimuli required
  for detection 50 of the time (the smallest
  change in stimulus needed to detect that change)
• AKA- just noticeable difference (JND)

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Absolute threshold

• An absolute threshold is not absolute
• What factors might affect the absolute threshold?
• Repetition
• Fatigue
• Competing stimuli
• Expectation

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Sensation- Thresholds

• Webers Law- percentage or ratio of difference
  between objects remains constant for JND, even
  when weight or dimensions change
• light intensity- 8
• weight- 2
• tone frequency- 0.3

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Webers Law

• As a salesman, how might one use Webers law to
  increase chances of selling the following to one
  customer?
• Built in ipod accessory 100
• New Truck 25,000
• Navigation system 200
• Sliding rear window 125

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Sensation- Thresholds

• Signal Detection Theory
• predicts how and when we detect the presence of a
  stimulus (signal) amid competing stimuli (noise,
  objects etc.)
• assumes that there is no single absolute
  threshold
• Factors influencing detection (response criteria)
• experience
• expectations
• motivation
• level of fatigue

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Vision Sensory Adaptation

• Sensory adaptation- diminished sensitivity to
  stimulus as a consequence of constant exposure
• Eyes constant quiver to ensure enough continual
  stimulation to eyes receptors
• Otherwise full visual image is lost

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Vision- Stabilized Images on the Retina
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Sensation- Thresholds

• Subliminal
• When stimuli are below ones absolute threshold
  for conscious awareness

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1957

• James Vicary
• 1/3000 second
• Repetition
• Sales increase
• Popcorn 57
• Coke 18
• 6 week study
• Falsified results
• Gateway to subliminal marketing, then
  images,sexploitation

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Priming Effect

• Feel what we do not know and cannot describe
  (shapes our perceptions a tiny bit without our
  awareness)
• subliminal images Imperceptibly brief stimulus

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Whats the reasoning?

• The average American will see over 6 million ads
  in a lifetime
• Appeal to the subconscious will make consumer
  feel more positively about a product

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Envelopes, Quarters and boxes.(Meyers, p. 7)

• Can you detect a difference in weight between the
  two envelopes?
• Can you detect a difference in weight between the
  two envelopes now?
• How can we explain this development?

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Vision

• How do we transform particles of light into
  meaningful images?
• Transduction
• conversion of one form of energy to another
• in sensation, our sensory systems transform
  stimulus energies into neural impulses

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Vision

• Two physical characteristics of light help
  determine how we visually sense them
• 1. Wavelength
• the distance from the peak of one wave to the
  peak of the next (determines hue)
• Hue color we see determined by wavelength of
  light
• 2. Intensity
• amount of energy in a light wave determined by
  amplitude
• brightness
• or loudness

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Wavelengths and Color

• From shortest to longest
• Violet
• Indigo
• Blue
• Green
• Orange
• Red
• (We turn our eye towards an object and the
  reflected light coming from the object enters our
  eye.)

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Vision- Physical Properties of Waves (from an
atom to a mile)
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The spectrum of electromagnetic energy (light
that we transduce into color)
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Vision
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Match the following

1. Adjustable opening in the center of the eye
2. Ring of muscle, color portion of the eye around
   pupil- controls size of pupil opening
3. Transparent- behind pupil, changes shape to focus
   images on retina
4. Protects eye, bends light to provide focus
5. Eyes light sensitive inner surface- rods, cones,
   neurons that process visual info.

• Cornea
• D
• Pupil
• A
• Iris
• B
• Lens
• C
• Retina
• E

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Vision

• Accommodation- the lens changes shape to help
  focus near or far objects on the retina
• Retina- the light-sensitive inner surface of the
  eye, containing receptor rods, cones and layers
  of neurons that begin the processing of visual
  information (transduction)

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Retinas Reaction to Light- Receptors

• Rods (120 million!)
• peripheral retina / peripheral vision
• detect black, white and gray
• twilight or low light
• Cones (6 million)
• near center of retina (Fovea)
• fine detail and color vision
• daylight or well-lit conditions

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Rods and Cones
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Making sense of our vision

• So why is our peripheral vision more blurred than
  our focused vision? (in front of us)
• Cones center of retina (fovea hotline to
  visual cortex fine detail)
• Rods periphery of retina
• How do you walk effectively on a trail on a very
  dark night? Why?
• Why can a cat see better than us at night?

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Vision- Receptors
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From the eye to the brain

• Optic Nerve
• Rope-like axons form ganglion cells- carries
  information from the eye to the brain (1,000,000
  messages at once!)

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Close your left eye- move forward to a spot in
which the car disappears. What is this called?
How do we explain it?
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Retinas Reaction to Light

• Blind Spot- point at which the optic nerve leaves
  the eye- creates blind spot because no receptor
  cells located there
• Fovea- central point in the retina, around which
  the eyes cones cluster (contains only cones-
  direct connection to visual cortex through
  bipolar cells fine detail)

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Vision

• Acuity- the sharpness of vision
• Nearsightedness- nearby objects are more clear
  than distant objects because distant objects in
  front of retina
• Farsightedness- faraway objects are more clear
  than near objects because the image of near
  objects is focused behind retina

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Vision

• Normal Nearsighted Farsighted
  Vision Vision Vision

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Pathways from the Eyes to the Visual Cortex
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Visual Information Processing

• Retina Brain tissue / analyzes, encodes info
  routes to Thalamus
• Process becomes more complex as continues

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Visual Information Processing

• Feature Detectors
• (Hubel and Wiesel, 1979)
• Specific parts of the visual cortex respond to
  specific features (routed by Thalamus)
• shape
• angle
• movement

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Parallel Processing

• feature detection is integrated in visual cortex
  in split second
• IOW angle, shape motion, depth etc of object are
  all processed in different parts of cortex and
  then instantly combined to create whole visual
  image)

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Parallel Processing
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Parallel Processing

• Facial recognition 30 of cortex
• Neural networks synchronized integration
• ¼ of second- neurons, parts of brain collaborate
  at once(40 impulses per second) conscious
  recognition!

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How does this explain Prosopagnosia?
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The Key to Perception

• Perception combining sensory input with
  assumptions, expectations

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How the Brain PerceivesStare at the Necker Cube.
What happens?
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How can we explain our changing perception of the
Necker Cube?

• Same image continues to meet your retina, your
  brain constructs varying perceptions every couple
  of seconds.

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Illusory ContoursStare at the center of the image
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Color Vision

• Light rays are not colored. Color, like all
  aspects of vision, resides not in the object but
  in the theater of our brains.
• Isaac Newton, 1704

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Hows Your Color Vision??

• http//www.neitzvision.com/

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Visual Information Processing

• Trichromatic (three color) Theory
• AKA Young and Helmholtz theory
• three different retinal color receptors (cones)
• red
• green
• Blue
• Combination of these cones all colors of
  visible spectrum
• Can not explain monochromatic / dichromatic color
  deficiency

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Color-Deficient Vision

• Dichromatic
• Monochromatic

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• Opponent-Process Theory- opposing retinal
  processes enable color vision (in retina
  thalamus, some neurons turned on/off by certain
  colors)
• ON OFF
• red green
• green red
• blue yellow
• yellow blue
• black white
• white black

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Opponent-Process Theory

• Helps explain monochromatic and dichromatic color
  deficiency (and afterimage)
• Most theorize that we use a combination of both
  major theories (need both to explain color vision
  fully)

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Visual Information Processing

• Color Constancy
• Perceiving familiar objects as having consistent
  color, even if changing illumination alters the
  wavelengths reflected by the object (perception
  of color comes from object and those things
  around it)

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Visual Disabilities

• Stroke, illness, surgery etc. can damage the
• visual cortex thus
• Stroke victim case studies who have lost sense of
  visual movement
• Blindsight sensation of vision is functional,
  but no perceptual awareness
• Thus theory of 2 visual systems in brain
• One for conscious perceptions
• A second that guides our actions

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