Chapter 4: Sensation and Perception

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Chapter 4 Sensation and Perception
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What are they?

• Sensation
• Process in which the sense organs receptor cells
  are stimulated and relay initial information to
  the brain for further processing
• Sensation requires transduction which is the
  change of physical energy to neural energy
• Perception
• Process by which organism selects and interprets
  sensory input so that it acquires meaning (Do
  something about it)
• How do you study it?
• Bottom Up Stimuli to concept
• Top Down Concept to stimuli

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The Perceptual Process
The steps in this process are arranged in a
circle to emphasize the fact that the process is
dynamic and continually changing. Blue arrows
point to stimuli green to processing red to
perceptual responses. Arrows A, B, and C
indicate three important relationships that
researchers measure.
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The Senses

• Vision
• Hearing
• Touch
• Taste
• Smell

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Vision The Stimulus

• Light electromagnetic radiation
• Amplitude perception of brightness
• Wavelength perception of color
• Purity mix of wavelengths
• perception of saturation, or richness of colors.

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The EyeA Living Optical Instrument

• The eye housing and channeling
• Components
• Cornea where light enters the eye
• Lens focuses the light rays on the retina
• Iris colored ring of muscle, constricts or
  dilates via amount of light
• Pupil regulates amount of light

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The Retina The Brains Envoy in the Eye

• Retina absorbs light, processes images
• Optic disk optic nerve connection/blind spot
• Receptor cells
• Rods black and white/low light vision
• Cones color and daylight vision
• Adaptation becoming more or less sensitive to
  light as needed

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Retinal Processing

• Differences between rods and cones
• Shape
• Rods - large and cylindrical
• Cones - small and tapered
• Distribution on retina
• Fovea consists solely of cones
• Peripheral retina has both rods and cones
• More rods than cones in periphery

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Figure 4.4 The retina
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Figure 4.6 Receptive fields in the retina
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Adaptation

• Progressive loss of response when stimulation is
  maintained
• Form of information suppression that prevents the
  nervous system from becoming overwhelmed by
  stimuli that offer very little news about the
  world.

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Vision and the Brain

• Light ? rods and cones ? neural signals ? optic
  nerve ? optic chiasm ? opposite half brain
• dorsal where
• ventral what

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Figure 4.7 Visual pathways through the brain
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Figure 4.9 The what and where pathways from the
primary visual cortex
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Information Processing in the Visual Cortex

• Early 1960s Hubel and Wiesel
• Microelectrode recording of axons in primary
  visual cortex of animals
• Discovered feature detectors neurons that
  respond selectively to lines, edges, etc.
• Groundbreaking research Nobel Prize in 1981
• Later research cells specific to faces in the
  temporal lobes of monkeys and humans

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Theories of Color Vision

• Trichromatic theory - Young and Helmholtz
• Receptors for red, green, blue color mixing
• Opponent Process theory Hering
• 3 pairs of antagonistic colors
• red/green, blue/yellow, black/white
• Current perspective both theories necessary

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Perceiving Forms, Patterns, and Objects

• Reversible figures
• Perceptual sets
• Inattentional blindness
• Feature detection theory - bottom-up processing
• Form perception - top-down processing
• Gestalt psychologists the whole is more than
  the sum of its parts
• Reversible figures and perceptual sets
  demonstrate that the same visual stimulus can
  result in very different perceptions
• Video!

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Figure 4.16 Feature analysis in form perception
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Figure 4.17 Bottom-up versus top-down processing
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Principles of Perception

• Gestalt principles of form perception
• figure-ground
• Proximity
• closure
• similarity
• simplicity
• and continuity

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Figure 4.18 The principle of figure and ground
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Figure 4.21 A famous reversible figure
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Figure 4.22 The Necker cube
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Perceptual Constancies in Vision

• Perceptual constancies stable perceptions amid
  changing stimuli
• Size
• Shape
• Brightness
• Hue
• Location in space

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Pictorial Cues and Depth Perception

• Or - figuring out where things are in space

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• A scene in Tucson, Arizona containing a number of
  depth cues occlusion (the cactus occludes the
  hill, which occludes the mountain) perspective
  convergence (the sides of the road converge in
  the distance) relative size (the far motorcycle
  is smaller than the near one) and relative
  height (the far motorcycle is higher in the field
  of view the far cloud is lower).

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• Atmospheric perspective - distance objects are
  fuzzy and have a blue tint

• A scene along the coast of California that
  illustrates atmospheric perspective.

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• Figure 8.6 A texture gradient in Death Valley,
  California.

• Texture gradient - elements are more closely
  packed as distance increases

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Shadows - indicate where objects are located

• (a) Occlusion indicates that the tapered glass is
  in front of the round glass and vase. (b)
  Overlap now indicates that the vase is in front
  of the tapered glass, but there is something
  strange about this picture. (c) The cast shadow
  under the vase provides additional information
  about its position in space, which helps clear up
  the confusion.

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The Power of Misleading CuesVisual Illusions

• Optical Illusions - discrepancy between visual
  appearance and physical reality
• Famous optical illusions Muller-Lyer Illusion
  and Impossible Figures

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Figure 4.28 The Muller-Lyer illusion
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Figure 4.29 Explaining the Muller-Lyer Illusion
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Figure 4.32 Three classic impossible figures
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Hearing The Auditory System

• Stimulus sound waves (vibrations of molecules
  traveling in air)
• Amplitude (loudness)
• Wavelength (pitch)
• Purity (timbre)
• Wavelength described in terms of frequency
  measured in cycles per second (Hz)
• Frequency increase pitch increase

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Sensory Processing in the Ear

• External ear (pinna) collects sound
• Middle ear the ossicles (hammer, anvil, stirrup)
• Inner ear the cochlea
• a fluid-filled, coiled tunnel
• contains the hair cells which are auditory
  receptors
• lined up on the basilar membrane

Figure 4.35 The human ear
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Figure 4.36 The basilar membrane
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How do we hear?
1. The pinna (outer ear) catches sound waves 2.
Sound waves are amplified and transduced from
air pressure into mechanical energy by
cochlea 4. The vibration causes the
basilar membrane to move and subsequently causes
the cilia of the outer hair cells to bend
converting mechanical energy into neural energy
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Theories of Hearing Place or Frequency?

• Hermann von Helmholtz (1863)
• Place theory where on the basilar membrane
• Other researchers (Rutherford, 1886)
• Frequency theory how quickly the basilar
  membrane vibrates
• Georg von Bekesy (1947)
• Traveling wave theory

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The Chemical Senses Taste

• Taste (gustation)
• Physical stimulus soluble chemical substances
• Receptor cells found in taste buds
• Pathway taste buds - neural impulse - thalamus
  - cortex
• Four primary tastes sweet, sour, bitter, and
  salty

The tongue is most sensitive to these basic
tastes in certain regions
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The Chemical Senses Smell

• Smell (Olfaction)
• Physical stimuli substances carried in the air
• dissolved in fluid, the mucus in the nose
• Olfactory receptors olfactory cilia
• Pathway Olfactory cilia - neural impulse -
  olfactory nerve - olfactory bulb (brain)
• Does not go through thalamus

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Sensory HomunculusLatin for "little man"
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Skin Senses Touch

• Physical stimuli mechanical and thermal energy
  impinging on the skin.
• Receptive fields
• Pain receptors free nerve endings in skin
• Two pain pathways fast vs. slow
• Gate-control theory

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Slow Throbbing
Fast Sharp
Figure 4.40 Pathways for pain signals