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Sensation

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Sensation & Perception Chapter 4 – PowerPoint PPT presentation

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Title: Sensation


1
Sensation Perception
  • Chapter 4

2
Transduction
  • Transduction Transformation of one form of
    energy into another especially the
    transformation of stimulus information into nerve
    impulses
  • Receptors Specialized neurons that are
    activated by stimulation and transduce (convert)
    it into a nerve impulse
  • Sensory pathway Bundles of neurons that carry
    information from the sense organs to the brain

3
Sensation and Perception
  • Sensation Neurons in a receptor create an
    internal pattern of nerve impulses that represent
    the conditions that stimulated it
  • Perception A process that makes sensory
    patterns meaningful and more elaborate
  • Stimulation ? Transduction ? Sensation ?
    Perception

4
Sensory Adaptation
  • Sensory adaptation Loss of responsiveness in
    receptor cells after stimulation has remained
    unchanged for a while
  • Examples???

5
Thresholds
  • Absolute threshold Amount of stimulation
    necessary for a stimulus to be detected (50 of
    time)
  • Difference threshold Smallest amount by which a
    stimulus can be changed and the difference be
    detected (also called just noticeable difference
    JND)

6
Looking at the JND
  • Webers law The JND increases with the
    magni-tude of the stimulus.
  • The JND is large when the stimulus intensity is
    high, and small when the stimulus intensity is
    low
  • TV (volume high turn down a lot, volume low
    turn down little)
  • Groceries (50 pound bag need to add more than
    you would to a 25 pound bag)
  • Stevens power law
  • Used for wider array of stimuli (shock,
    temperature)
  • Fills in gaps left by Weber and Fechner

7
Signal Detection Theory
  • Signal detection theory Perceptual judgment as
    combination of sensation and decision-making
    processes
  • Based on each individuals sensitivity and
    response criterion
  • Example holiday weekend on the interstate
  • False Alarm (brakes and no cop)
  • Hit (brakes and cop)
  • Miss (no brakes and cop)
  • Correct Rejection (no brakes and no cop)
  • Lowers response criterion and raises hit rates
  • Flawed merchandise off the assembly line
  • TSA putting weapons in bags

8
Subliminal Persuasion
  • Studies have found that stimuli flashed
    subliminally on a screen can prime a persons
    later responses.
  • No controlled research has ever shown that
    subliminal messages delivered to a mass audience
    influences buying habits.
  • Subtle, fleeting effect on thinking
  • No powerful, enduring effect on behavior

9
The Anatomy of Visual Sensation
  • Photoreceptors Light-sensitive cells in the
    retina that convert light energy to neural
    impulses
  • Rods Sensitive to dim light but not colors
  • Cones Sensitive to colors but not dim light
  • http//www.youtube.com/watch?vx6Ua5d3wlA0 (632)

Fovea Area of sharpest vision in the retina
10
The Anatomy of Visual Sensation
  • Optic nerve Bundle of neurons that carries
    visual information from the retina to the brain
  • Rods/cones?bipolar cells?ganglion cells

Blind spot Point where the optic nerve exits
the eye and where there are no photoreceptors
(money in the bank demo)
11
Color Blindness Afterimages
  • Color blindness Vision disorder that prevents
    an individual from discriminating certain colors
  • Red-green is most common!
  • Afterimages Sensations that linger after the
    stimulus is removed
  • Fix your eyes on the center for a negative
    afterimage

12
How the Visual System Creates Color
  • Visual cortex Part of the brain the occipital
    cortex where visual sensations are processed
  • Brightness Sensation caused by the intensity of
    light waves
  • Color Psychological sensation derived from the
    wavelength of visible light color, itself, is
    not a property of the external world
  • Electromagnetic spectrum Entire range of
    electromagnetic energy, including radio waves,
    X-rays, microwaves, and visible light
  • Visible spectrum Tiny part of the
    electromagnetic spectrum to which our eyes are
    sensitive

13
How the Visual System Creates Brightness
Wavelength
Intensity (amplitude)
Color
Brightness
14
Sensing Colors
  • Trichromatic Theory Idea that colors are sensed
    by three different types of cones sensitive to
    light in the red, blue and green wavelengths.
  • Explains the earliest stage of color sensation.
  • Opponent-process Theory Idea that cells in the
    visual system process colors in complimentary
    pairs, such as red or green or as yellow blue.
  • Explains color sensation from the bipolar cells
    onward in the visual system.

15
Hearing How Sound Waves Become Auditory
Sensations
Pinna ? Ear Canal ? Tympanic Membrane ? Middle
Ear ? Oval Window ? Cochlea (Basilar Membrane) ?
Auditory Nerve
16
Hearing How Sound Waves Become Auditory
Sensations
17
Hearing How Sound Waves Become Auditory
Sensations
Cochlea
18
Hearing How Sound Waves Become Auditory
Sensations
19
Deafness
  • Conduction deafness Results from damage to
    structures of the middle or inner ear
  • Nerve deafness Linked to a deficit in the
    bodys ability to transmit impulses from the
    cochlea to the brain
  • Usually involves the auditory nerve or higher
    auditory processing centers

20
Hearing The Physics of Sound
  • Loudness produced by the amplitude of a sound
    wave

- Amplitude Physical strength of a wave
21
Hearing The Physics of Sound
  • Pitch produced by the frequency of a sound wave
  • Frequency Number of cycles completed by a wave
    in a given amount of time

22
How Sound Waves Become Auditory Sensations
  • Pitch
  • Place Theory different places on the basilar
    membrane send neural codes for different pitches
  • Frequency Theory neurons have different firing
    rates for different sound wave frequencies
  • Timbre Quality of a sound wave that derives
    from the waves complexity
  • Auditory cortex Portion of the temporal lobe
    that processes sounds

23
Position and Movement
  • Vestibular sense Sense of body orientation with
    respect to gravity
  • http//www.youtube.com/watch?vx6Ua5d3wlA0 (721)
  • Kinesthetic sense Sense of body position and
    movement of body parts relative to each other

24
Smell
  • Olfaction Sense of smell
  • Olfactory bulbs Brain sites of olfactory
    processing
  • Pheromones Chemical signals released by
    organisms to communicate with other members of
    the species

25
Smell
26
Taste
  • Gustation The sense of taste

Taste buds Receptors for taste (primarily on
the upper side of the tongue)
27
The Skin Senses and Pain
  • Gate-control Theory An explanation for pain
    control that proposes we have a neural gate
    that can, under some circumstances, block
    incoming pain signals.
  • Placebos Substances that appear to be drugs but
    are not
  • Placebo effect A response to a placebo caused
    by subjects belief that they are taking real
    drugs

28
The Machinery of Perceptual Processing
  • Percept Meaningful product of a perception
  • Feature detectors Cells in the cortex that
    specialize in extracting certain features of a
    stimulus
  • Binding problem A major unsolved mystery in
    cognitive psychology, concerning the physical
    processes used by the brain to combine many
    aspects of sensation to a single percept

29
Bottom-Up and Top-Down Processing
  • Bottom-up processing Analysis that begins with
    the sense receptors and works up to the brains
    integration of sensory information
  • http//www.youtube.com/watch?vx6Ua5d3wlA0 (50)
  • Top-down processing Analysis guided by
    higher-level mental processes - emphasizes
    perceiver's expectations, memories, and other
    cognitive factors
  • http//www.youtube.com/watch?vx6Ua5d3wlA0 (144)

30
Perceptual Constancies
  • Perceptual constancy Ability to recognize the
    same object under different conditions, such as
    changes in illumination, distance, or location
  • Shape, color, size

31
Perceptual Illusions
32
Perceptual Ambiguity and Distortion
  • Illusions Distortion of a stimulus pattern,
    shared by others in the same perceptual
    environment
  • More likely when
  • stimulus is unclear
  • info is missing
  • elements combined in unusual ways
  • familiar patterns arent apparent
  • Ambiguous figures Images that are capable of
    more than one interpretation

33
The Gestalt Approach
  • Gestalt psychology View that much of perception
    is shaped by innate factors built into the brain
    (nature)
  • The whole pattern is greater than the sum of its
    parts.
  • Figure Part of a pattern that commands
    attention
  • Ground Part of a pattern that does not command
    attention the background

34
The Gestalt Approach
  • Subjective contours Boundaries that are
    perceived but do not appear in the stimulus
    pattern
  • Closure Tendency to fill in gaps in figures and
    see incomplete figures as complete

35
The Gestalt Laws of Perceptual Grouping
Proximity
Similarity
Closure
Continuity
Common Fate
Prägnanz
36
Binocular Cues two eye depth cues
  • Binocular Convergence lines of vision from each
    eye converge at different angles on objects at
    different distances
  • Can feel eye muscles change as you focus at
    different distances
  • Retinal Disparity difference in perspectives of
    the 2 eyes (greater disparity for nearby objects
    provides us with depth information)

37
Monocular Cues one eye depth cues
  • Monocular Cues
  • Linear Perspective parallel lines appear to meet
    in the distance

38
Monocular Cues one eye depth cues
  • Monocular Cues
  • Relative Motion objects closer to you move
    faster than those further away from you

39
Monocular Cues one eye depth cues
  • Monocular Cues
  • Relative Size 2 objects the same size the one
    that appears larger closer to us

40
Monocular Cues one eye depth cues
  • Monocular Cues
  • Interposition hidden objects are more distant
    than those objects that hide them

41
Monocular Cues one eye depth cues
  • Monocular Cues
  • Texture Gradient as object gets further away
    from us, the texture gets smoother

42
Theoretical Explanations for Perception
  • Learning-based inference View that perception
    is primarily shaped by learning, rather than
    innate factors (nurture) opposite of Gestalt
  • What determines how successful we will be in
    forming an accurate percept?
  • Context, expectation, perceptual set each
    influenced by culture
  • Perceptual set Readiness to detect a particular
    stimulus in a given context

43
Cultural Influences on Perception
A
B
Which box is bigger, A or B?
44
Muller-Lyer Illusion
  • When 2 objects make the same size image on the
    retina, and we judge one to be farther away than
    the other, we assume that the more distant one is
    larger.
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